Malaria and other tropical diseases

Delivered 23^rd October 1946

 

By

Sir Neil Hamilton Fairley

Much of the subject matter of this lecture deals with advances in know­ledge made during the war in the chemotherapeutic control of tropical disease and the chemical control of insect vectors obtained from experi­ments on human volunteers. However, the fundamental work of placing these chemotherapeutic and chemical agents at our disposal was initially made possible only by large scale animal experi­ments. New anti-malarial drugs, of which many thousand were synthesised during the war, had to be tested in the first instance on birds infected with different species of bird malaria. Similarly, the toxicity of such insecticides as D.D.T. and dimethylphthalate had to be investigated for toxicity in animals; had this not been done their use by man would have been greatly curtailed.

Casualties from Tropical Diseases

During the Second World War the disease problems in the Pacific and South East Asia Commands were in the main similar, and it is proposed mainly to limit this lecture to a review of research bearing on the control of the more important tropical diseases common to these two areas.

During the early campaigns against the Japanese in 1942-1943 casualties from sickness were 5 to 30 times as common as battle casualties. Malaria and dysentery were particularly problematic. This experience was common to British and Indian troops in Burma, U.S.A. troops at Bataan and Guadalcanal, and Australian troops in New Guinea and New Britain.

 

Owing to the numerous diseases transmitted by biting insects, the clothing of the soldier in the jungle was of major importance and the use of insecticides and insect repellents essential. Shorts were unsuitable for they increased the surface area of exposure to trauma and insect bites. In conse­quence, they increased the tendency to tropical ulcers, septic sores, the mosquito-transmitted diseases—malaria, dengue and filariasis—and limited the effective application of anti-mite fluid (bibutyl phthalate or dimethyl phthalate) in controlling mite typhus. While warfare was static a high standard of military hygiene and sanitation enabled tropical disease casualties to be kept within reasonable limits. On the other hand, in a war of movement, and especially in jungle warfare, effective prevention became most difficult and chemotherapeutic control of diseases like malaria and dysentery was indispensible. 

 

An example of the risks involved is afforded in the Huon Peninsula and Markham-Ramu Valley campaigns in New Guinea. On September 4^th 1943 Australian troops landed on the shores of Huon Gulf Peninsula. This was rapidly suc­ceeded by an aerial operation in the Markham Valley. In the subsequent six months, battle casualties were 3,140, and disease casualties 47,543; the ratio of disease; battle casualties being approximately 15:1. The incidence of different diseases is given in the table below.

 

Medical Casualties in New Guinea in the Australian Military Forces  

(Huon Peninsula Campaign—September, 1943-February, 1944)

 

Disease	Number	Percent
Malaria                              Dengue                Dysentery* and diarrhoea Scrub typhus                         Skin and other diseases	28,909    8,813      3,157      1,315      5,340	60.8          17.5          6.6              2.7            11.2
Total	47,534	100

 

 

 

 

 

 

 

 

* Amoebic and bacillary inclusive

Battle casualties approximately = 3,140
Sickness as above = 47,534

Total casualties = 50,674

Ratio of medical:battle casualties = 15: 1 

Research measures directed to the gaining of new knowledge on these diseases and their control are reviewed below.

 

The Chemotherapeutic Control of Malaria in War

Prior to the recent world war our knowledge of the protection which could be afforded by regularly taking small doses of anti-malarial drugs in individuals not previously infected with malaria (non-immunes) was very inadequate. Quinine had been extensively used as a suppressant to prevent attacks of malaria fever in the First World War with results which, though useful, proved far from satisfactory. At the outbreak of war in 1939, Germany was still the main manu­facturer of atebrin (mepacrine) and until after the fall of Java, early in 1942, there was no large scale commercial production in either England or U.S.A. The position in regard to the suppressive and possible prophylactic value of atebrin (mepacrine) in malaria was critically reviewed by Field (1939), who concluded that regular daily prophylactic quinine was still to be recommended in preference to 0.2 grammes of atebrin twice weekly owing to yellow staining of the skin, and possible toxic complications, such as mental disturbances and damage to the liver. The freedom from harmful side effects weighed heavily in favour of small daily doses of quinine. At the onset of war in 1939, the status of atebrin as a suppressive or casual prophylactic drug was uncertain. 

 

In 1942 and early 1943 malaria casualties in the South West Pacific in a period of four months amounted to approximately 90 per cent of the forces involved. Up to this time, quinine (10 grains daily¹) had mainly been used as a suppressant. The type of malaria breakdown had been constant at Rabaul and in the New Guinea campaigns, malignant tertian malaria accounting for approximately 80 to 90 per cent of overt attacks during actual jungle fighting and the remaining 10 to 20 per cent being caused by benign tertian malaria. Later, after a full course of quinine-atebrine-plasmoquine therapy, troops relapsed with benign tertian malaria, reappearance of malignant tertian malaria being most uncommon provided re­infection had not taken place. The problem was one of extreme gravity.

A medical research unit was established at Cairns, in Northern Queensland, composed of medical specialists, entomologists, parasitologists and biochemists for the purpose of investigating the sup­pressive and casual prophylactic action of various anti-malarial drugs in experimentally infected volunteers. During these researches, 850 healthy volunteers were experimentally infected with sporozoite-induced malaria, using strains of P. falciparum and P. vivax from New Guinea and New Britain.

 

Experimental Results Obtained by Land Headquarters, Australia Medical Research Unit

From 1943 to 1946, the drugs studied included quinine, plasmoquine, sulphadiazine, sulphamerazine, atebrin (mepacrine), the 4-amino-quinolines-sontochin (SN. 6911) and resochin or chloroquin (S.N. 7618), sent for investigation by the National Research Council, U.S.A., and the biguanides, N.4430 and paludrine (M. 4888), sent for testing through the Medical Research Council, U.K. A special feature of the investigation was the routine sub-inoculation with large quantities of blood (200c.c.) of non-­immune volunteers to determine the presence or absence of infection in the donor at a time when thick films examined microscopically proved negative for malaria parasites. The quantity examined as a routine was 10c.mm, this took about one hour per patient per day.

 

The first three drugs investigated in experimentally infected volunteers were quinine, sulpha drugs of the sulphadiazine group and atebrin (mepa­crine). The results, which are summarised below, were reported in detail by Fairley and his colleagues (1945).

 

(a) Quinine

It was found that daily quinine failed to suppress both malignant tertian and benign tertian malaria infec­tions satisfactorily. When the dosage was increased to 20 grains daily, suppression and radical cure of malignant tertian infections was achieved, and suppression of benign tertian occurred throughout the period of drug administration; overt B.T. malaria developed after cessation of quinine. As the dosage of 20 grains of quinine daily produced toxic symptoms if prolonged indefinitely, it was evident that quinine was not a really satis­factory suppressant in jungle warfare in New Guinea.

 

(b)   Sulphadiazine group of drugs

With sulphadiazine it was found that volunteers receiving 0.5 to 1.0 grams daily were fully protected from heavy malignant tertian infections. Suppression being satisfactory and radical cure attained provided the daily dosage was continued for three weeks after last exposure. But when volunteers were bitten by mosquitoes harbouring the sporozites of Plasmodium vivax in their salivary glands, overt attacks of benign tertian malaria occurred even when taking daily doses (1.0 grams) of the drug. Similar results were obtained with sulphamerazine and sulphamezathine. It was evident that drugs of the sulphadiazine group were not suitable suppressants of malaria in New Guinea, where most troops acquired both malignant tertian and benign tertian infections. The result was particularly disappointing as sulphamerazine had been shown to possess causal prophylactic properties for one species of bird malaria (P. gallinaceum) by U.S.A. scientists, and similar results were hoped for with the species of malaria parasite affecting man. 

 

(c) Atebrin (mepacrine)

In 1943 excellent results were obtained in volunteers at Cairns who had received one tablet (0.1 gram) of atebrin on every day of the week for four weeks prior to exposure to infection, during the period of exposure and for 23 days after the last infective bite (New Guinea strains). Control volunteers who were taking no drug were bitten by the same number of infected mosquitoes from the same batch and invariably developed malaria.

 

Benign tertian malaria

Volunteers exposed to bites of mosquitoes proved to be infected with Plasmodium vivax failed to develop attacks of overt malaria provided they were receiving atebrin with unvarying regu­larity in the above dosage. Clinical malaria associated with parasites, how­ever, developed later, fever appearing in 14 to 44 days and parasites from 19 to 46 days after drug administration ceased. 

 

Malignant tertian malaria

Volunteer receiving 10 to 21 infective bites (Plasmodium faciparum) failed to develop overt malaria when following a similar atebrin regimen of one tablet (0.1 gram) daily. Slight transient rises in temperature and generalised aches and pains sometimes were noted, but such symptoms were never sufficiently severe to necessitate the volun­teers reporting sick or going to bed, and they invariably carried on their routine daily activities which were considerable. In these volunteers para­sites could not be demonstrated in thick films even though 1 to 2 c.mm. of the blood were examined. Furthermore, after cessation of the drug overt malaria never developed. Inoculation with 200 c.c. of the blood, collected after atebrin medication ceased, also failed to produce malaria in non-­immune volunteer recipients. In contrast to this, earlier subinoculation from these volunteers made from the seventh to the tenth day following infection had revealed the blood was infective even though parasites could not be demonstrated microscopically for the recipients developed malaria. It was therefore evident that in volunteers infected with malignant tertian malaria atebrin was not acting by preventing infection but was¹ producing radical cure by destroying the young asexual parasites soon after they had gained access to the circulation on the seventh day following exposure to infection.  

Mixed infections with P. falciparum and P. vivax

Reference has been made to the fact that in jungle warfare troops were generally infected with both benign tertian and malignant tertian malaria. To reproduce field condi­tions experimentally, it was necessary to infect volunteers repeatedly over a period of several months by exposure to different batches of infective mosquitoes harbouring P. vivax or P. falciparum.   In addition, it was essential to subject volunteers to all conditions which might favour malaria relapses, such as physical fatigue, cold, annoxia, blood loss, etc. All this was done, but in no instance did overt malaria develop while they were taking their daily dose of atebrin. On an average of 30 days following cessation of atebrin, the volunteers developed overt benign tertian malaria, but never malignant tertian malaria.

These experiments were of profound significance from a military point of view for they proved that, provided troops took atebrin in adequate daily dosage, they could go into hyperendemic areas of malaria and fight for indefinite periods in the jungle without significant malaria casualties. The experimental results indicated there should be no deaths, no malaria carriers in the force and no blackwater fever—provided the daily dose was con­tinued for three to four weeks after leaving the endemic area. After stop­ping atebrin, troops infected with latent benign tertian malaria (P.vivax) would develop overt attacks. Subsequent experience in the field fully confirmed these experimental findings as is recorded later.

 

Atherton Conference on Prevention of Disease in Tropical Medicine 

In the Australian Army the question was often asked by field com­manders and medical officers regarding the efficacy of anti-malaria measures advocated by the Medical Directorate, and whether suppressive anti-malaria drugs could control the repeated malaria infections contracted in jungle warfare. The experiments, as outlined above, were devised and under­taken to get pertinent data which would answer this question. These data, which were presented to the Australian Army General Staff and Field Commanders at the Atherton Conference, were officially accepted as prov­ing that a correct atebrin regimen would lead to the chemotherapeutic control of malaria and enable troops to fight in the jungle with a minimum of malaria casualties. Subsequently, knowledge regarding atebrin adminis­tration and personal protection became an essential part of a soldier's training for jungle warfare, and the institution of anti-malaria measures and atebrin-suppressive medication a matter of strict military discipline.

Subsequent Results in the Field

Reference has already been made to the devastating malaria casualties in New Guinea in 1942 to 1943. Consequent on the establishment of a high standard of atebrin discipline, malaria rapidly came under control. From December, 1943, the malaria rate* in Australian troops in hyperen­demic areas of malaria fell from 740 per 1,000 per annum to 26 per 1,000 per annum in November, 1944. It rose slightly to 75 per 1,000 per annum in January, 1945, decreased again to 39 per 1,000 per annum in March, then rose to 195 per 1,000 per annum in June. Thereafter it declined, reaching 60 per 1,000 in August, and 29 per 1,000 in September, which low level was subsequently maintained.

 

Malaria constituted no operational problem in the Solomons, New Britain and Borneo campaigns. Out of a total force of 130,000 troops at variable risk in hyperendemic areas of malaria outside New Guinea for approximately 6 to 12 months, there were only 1,256 malaria admissions to hospital, i.e., 0.9 per cent, while on an atebrin regimen of one tablet daily (0.1 gram).

 

In New Guinea itself the malaria incidence was very low except on the northern coast line at Aitaipe and Wewak. Here a definite epidemic of malignant tertian malaria occurred in April-July, 1945. Out of a total force of 23,000 some 5,377 individual (23.3 per cent.) had overt attacks. The average attack per patient over a period of over 11 months was 1.28. Only four deaths from malaria occurred, the case mortality being 0.06.

 

Extensive investigations indicated that most of the malaria casualties at Wewak were due to irregular atebrin intake. The prevalent strain of P. falciparum was atebrin-susceptible, but a number of patients were proved to harbour a less atebrin-susceptible strain which required two tablets of atebrin (0.2 gramme) daily for effective suppression. Whether this was a naturally less susceptible strain of P. falciparum, whether the quality of enhanced resistance arose suddenly as a mutation, or whether decreased susceptibility to atebrin had been acquired through sub-optional dosage over a prolonged period was uncertain. The strain showed no decreased susceptibility to resochin or paludrine, and had either of these drugs been available they could have been substituted for atebrin with certainty of success.

 

The experimental data and the conclusions of the Atherton Conference were cabled to the War Office, London, and malariologists came to Cairns from India, U.S.A., and England to investigate the experimental back­ground of these human experiments. The Supreme Allied Commander of South East Asia, Admiral Lord Louis Mountbatten, accepted the results and their military implications in toto. Similar measures to ensure a high standard of atebrin discipline were established in South East Asia Com­mand and malaria rapidly passed under control.

 

Though Hill (1942) as a result of field experience in Africa had reached the conclusion that one tablet of atebrin daily (0.1 gramme) was an effective suppressant of malignant tertian malaria in troops operating in tropical areas, and though this dosage was ultimately adopted by the War Office, it needed a large scale experiment on human volunteers undertaken under arduous and trying conditions to convince medical and combatant officers alike of the extraordinary efficacy of such a regimen. This was probably attributable to the varying field reports received from time to time regarding its efficacy - some medical officers stating that atebrin was abso­lutely effective, others with equal conviction that it was not. Had it been possible to infect animals with human species of malaria parasites, the mode of action of this drug as a schizonticide in suppressing and curing malignant tertian malaria and in suppressing benign tertian malaria could have been demonstrated much earlier in the war, rendering human experi­ments unnecessary.

 

(d)   4-Amino-Quinolines

Sontochin and resochin (chloroquin) belong to the 4-amino-quinoline group of compounds. They were synthesised by German chemists and patented in England and elsewhere in 1939 before the war, though at this time they had not been subjected to extensive biological testing or adequate clinical study. During the war they were resynthesised in America and tested biologically on a large scale in both bird malaria and man. In 1944 the National Research Council, U.S.A., sent both these drugs to the L.H.Q. Medical Research Unit, Cairns, for investigation as suppressants and possible causal prophylactics in volunteers infected with P. vivax and P. falciparum. Both drugs proved to be essentially schizonticidal in action, did not discolour the skin and yielded therapeutic results comparable with atebrin. Though effective suppressants neither was found to be a causal prophylactic. The dosage of resochin is approximately half that of either sontochin or atebrin, and had the war continued it would probably have re­placed atebrin for suppressive purposes.

 

All the drugs so far investigated exerted suppressive effects through schizonticidal action after the parasites had appeared in the circulation in submicroscopic density - a finding established by extensive subinoculation experiments in Cairns. The anti-malarial drugs next to be considered were found to exert suppressive effects because they were causal prophylactics.

If a suppressant drug merely exerts an inhibitory action and delays the appearance of asexual parasites in the blood it is classed as a partial causal prophylactic; if it destroys the sporozoites or preerythrocytic forms so that asexual parasites never appear in the blood it is a true or complete causal prophylactic. It is in this sense that these terms are used in the present paper.

There are two groups of compounds possessing such an action, the 8-amino-quinolines, such as plasmoquine, and the biguanides like paludrine (M.4888) or M.4430 (N,-p-chlorphenyl-N,-methyl-N-,isopropyl-biguanide acetate) discovered in the pharmaceutical laboratories of I.C.I., Man­chester, by Curd, Davey and Rose (1945). Their brilliant researches rank with the discoveries of penicillin and D.D.T. and have profound medical significance.

 

(e) Plasmoquine

Time will not permit a detailed analysis of the Cairns' results, but it may be said that in general they confirmed those of James and his col­leagues (1935) that plasmoquine in large doses may act as a complete casual prophylactic in P.falciparum infection, and as a partial causal pro­phylactic in P.vivax malaria. The dosage of plasmoquine used, however, was far too large for routine purposes and cyanosis due to methaemoglo-binaemia was observed in 14 out of 21 volunteers receiving this order of dosage. 

 

(f) Paludrine 

Suppressive and Causal Prophylactic Action of Paludrine, P.falciparum When   volunteers were exposed   to   infective bites (P.falciparum), while taking paludrine in a daily dosage of 100 mg., which was continued for three weeks after exposure, no minor or major symptoms of malaria appeared, parasites were never demonstrable in the blood by microscopic examination, and subinoculation of 200 c.c. of blood from the seventh day onwards was invariably negative, the recipient never develop­ing malaria. The negative nature of the subinoculation results on the seventh day after exposure to infection was interpreted as indicating that the primary wave of asexual erythrocytic parasites from the pre-erythrocytic forms was either delayed or failed to appear at all. Subsequent failure to develop demonstrable blood parasites or overt attacks of malaria when drug administration ceased indicated that destruction of parasites in the pre-erythrocytic stage had been achieved. In other words the drug was acting as a complete or true causal prophylactic.

 

P. vivax

When volunteers were exposed to infective bites (P. vivax), while taking paludrine in a daily dose of 100 mg. which was continued in three weeks after exposure, neither major nor minor symptoms of malaria appeared and parasites were never demonstrable in thick blood smears. Subinoculation performed on the ninth day after exposure produced no evidence of malaria in the recipients which indicated that the primary wave of asexual erythrocytic parasites - presumably derived from the pre-ervthrocytic forms - had been delayed. After ceasing paludrine all these infected volunteers subsequently developed delayed attacks of overt vivax malaria. It was evident that in this dosage paludrine was acting only as a partial causal prophylactic. In another series, where the dosage was 300 mg. daily for 23 days, no evidence of malaria was found in a period of 93 to 141 days observation after exposure to infective biting. In some of these it may ultimately be found that paludrine has eradicated the infection completely. 

Mixed infections with P. falciparum and P. vivax

In field experiments volunteers received as many as 130 P. falciparum and 120 P. vivax infective bites while taking 100 mg. of paludrine daily. During this period they were subjected to severe stresses and strains, including (1) long marches in hilly country in a tropical climate varying from 30 miles in 24 hours to 89 miles in three days, (2) chilling by exposure in a freezing chamber for one hour at 10°C, (3) injections of adrenalin and insulin. The daily dose of paludrine was continued for four weeks after the last exposure to infec­tion which covered a period of two months. Throughout the three-month period no minor or major symtoms of malaria were noted and parasites were never demonstrable in thick blood smears. Some 24 to 33 days after the last dose of paludrine was administered overt vivax malaria developed, but never falciparum malaria.

 

These results confirmed conclusions already reached, namely, that palu­drine was a complete causal prophylactic for falciparum infection and a partial causal prophylactic against vivax infection in a dosage of 100 mg. daily. 

Single dose regimen (P.faciparum)

Subsequent experiments showed that paludrine in a single dose of 50 to 100 mg. given at 48, 72, 96 or 120 hours after exposure to heavy falciparum infection acted as a complete causal prophylactic, but that a single dose of 100 mg. given three hours before or 144 hours or more after exposure to infection failed to prevent overt malaria. This indicated that the pre-erythrocytic parasites were much more susceptible to the action of paludrine than either the sporozoites injected by the mosquito or the asexual erythrocyctic parasites. In larger doses the asexual parasites were destroyed by schizonticidal action, but it is doubtful if paludrine exerts any lethal action on the sporozoite.

The practical conclusion reached from this and other experiments is that paludrine in a dosage of one tablet (100 mg.) twice weekly, given at intervals of three or four days, will entirely prevent faciparum malaria developing in non-immune individuals, and will effectively suppress vivax malaria throughout the period of drug administration. The dosage regimen neces­sary to produce this result in individuals with some degree of pre-existing immunity remains to be worked out. 

 

Schizonticidal Action of Paludrine

The schizonticidal action of paludrine has been studied in detail by Maegraith and his colleagues (1945 - 1946) at the Liverpool School of Tropical Medicine and by Fairley and his colleagues (1946) at Cairns.

 

P. falciparum

Experiments in infected volunteers at Cairns have shown that parasites of P. falciparum appear in submicroscopic quantity in the blood from the seventh day (144 hours*) after exposure to infection, but that an additional three to four days generally elapse before parasites are demonstrable microscopically in thick blood films.

 

When volunteers were exposed to heavy biting with falciparum infected mosquitoes and paludrine was administered in a dosage of 100 to 300 mg. from the seventh to the twenty-first day radical cure of the infection by schizonticidal action results. Subinoculation on the seventh day was posi­tive in these cases, thus proving the donors had been infected. 

When hospital patients suffering from overt attacks of falciparum malaria received a course of 100 mg. of paludrine thrice daily for ten days, the clinical response was satisfactory, and parasites disappeared within two day in blood smears; 104 out of 105 such patients were radically cured. In our experience no other drug has proved as effective as paludrine in the radical sure of M.T. malaria (South West Pacific strains).

 

P.vivax

The response to paludrine of vivax infections acquired in India, Burma and the Mediterranean area has been investigated by Maegraith and his colleagues (1935-1936). Clinical cure was obtained in 147 cases of acute benign tertian malaria treated with paludrine in doses ranging from 10-700 mg. given every 12 hours for 14 to 28 days. No serious toxic effects of the drug were observed. In most cases the asexual parasites are reported to have disappeared from the blood by the fourth day of treatment and the sexual parasite by the fifth day.   There was rarely more than one rise of temperature above normal subsequent to the beginning of treatment.  

Variable dosage regimens have been and are being tried with paludrine in the treatment of relapsing vivax malaria in Australia. The clinical response was certainly not superior to that obtained with quinine or atebrin, and owing to the difficulty in differentiating between female gametocytes and degenerative trophozoites it was not always possible to determine with certainty - especially in thick blood films - when the asexual parasites finally disappeared. However, it may be stated that after 24 to 48 hours any parasites found were either degenerate trophozoites or gametocytes. Insu­fficient time has yet elapsed to assess the proportion of radical cures.

 

A three week course of paludrine followed by a maintenance dose of 100 mg. twice weekly for six months is regarded as holding out the best prospect of radical cure. A shorter course of paludrine (30 mg. daily) combined with plasmoquine (30 mg. daily) for 10 to 14 days also appears promising. The incidence of secondary attacks is similar to that obtained with com­bined quinine-plasmoquine treatment, but the interval between the cessa­tion of treatment and the onset of the secondary attack is twice as long in the paludrine-plasmoquine series. In the dosage given, i.e., 300 mg. daily, paludrine did not increase the toxicity of plasmoquine in the Australian series. Effects of single dosage. The administration of one single tablet (100 mg.) generally leads to disappearance of symptoms and of parasites from the blood smears in febrile attacks of malaria caused by either P. vwax or P. falciparum. Though clinical cure is generally attained with 100 mg. of paludrine, radical cure is not to be expected with so small a dosage and relapses follow in a few weeks. The possibilities of a single larger dose regimen of paludrine applied to the treatment of overt attacks of malaria under endemic or epidemic conditions open up a new field in chemothe­rapeutic control, while the institution of a bi-weekly regimen (100 mg.) in villages in hyper-endemic areas should prevent fresh infections with malignant tertian malaria altogether.

Dengue

The exceedingly rapid spread of dengue in the tropics and sub-tropics makes it a formidable disease when it affects troops not previously exposed to this infection. Though the disease is not fatal it may incapacitate the victims for three weeks or longer and rapidly prostrate a large proportion of the force. The common mosquito vector was first experimentally demon­strated in Queensland by Cleland, Bradley and MacDonald (1916) and (1918) to be Aëdes aegypti. Later, in the Philippines, Simmons (1931) showed that Aëdes albopictus also transmitted the disease.

Dengue is generally a disease of towns and on the Australian mainland troops living in camp contracted the disease only when they visit adjacent towns. In contrast to this it was found in New Guinea that dengue was affecting troops located in the jungle and coconut groves remote from native villages; furthermore, the usual vector, Aëdes aegypti, cduld not be found there. The presence of “jungle” dengue in the absence of Aëdes aegypti suggested another vector and Array investigations working under Lieut.-Colonel Ian Mackerras undertook an experimental investigation on this subject.

Experimental Transmission to Man

Mosquitoes of four different species were fed in the Finschafen area, New Guinea, on dengue patients during the first two days of fever, and subsequently sent by aeroplane to Sydney where dengue does not occur. The mosquitoes were kept at the Zoological Department, University of Sydney, and the human volunteers at 113th Australian General Hospital, under Captain P.G. Dowling. Three volun­teers, who received 32 to 82 bites from Aëdes scutellaris over a period of from 9 to 14 days each developed clinical dengue. On the other hand, three other volunteers bitten by Armigeres breinli, three bitten by Armigeres milnensis, and two bitten by Aëdes aurimargo failed to develop the disease. The infection was subsequently transmitted by sub-inoculation from the three cases bitten by Aëdes scutellaris to three new volunteers, and from them in turn to four other volunteers. Finally, two of the three original volunteers who had developed dengue after being bitten by Aëdes scutellaris were injected with blood containing dengue virus; they failed to become infected, thus demonstrating they had acquired immunity during their original attack.

 

Biology

The density of Aëdes scutellaris in and around camp sites was reported by Berrill and other Australian entomologists to be directly related to the number of cases of dengue occurring in that particular area. In breeding, Aëdes scutellaris showed a preference for clean rain-water, larvae breeding in hollow stumps, old coconut shells, the tops of oil and petrol drums and in the bifurcation of the branches of mango trees. The adults were generally found to enter tents and huts at approximately 7 to 8 a.m. and 4 to 7 p.m. On overcast days, however, mosquitoes of this species entered and were liable to bite all day long. During the day they rested in cool, damp, well-shaded situations under growing shrubs and bushes, protected from the rain and wind. Their flight range appears to be very limited - not exceeding 200 yards.

 

Control

Having demonstrated essential facts regarding the bio­logical habits of this vector, rational control measures were instituted. Breeding places in and around camps were eradicated and the adult mos­quitoes were destroyed by spraying tents, especially in the morning, (8 to 9 a.m.) and later afternoon (4 to 7 p.m.). The mosquito repellent, dimethyl phthalate, was applied by troops in the morning as well as late afternoon and evening. All febrile patients were kept under mosquito nets throughout the day and night. During outbreaks these measures were found to decrease markedly the number of troops affected.

 

Dysentery in War

Bacillary Dysentery

Bacillary dysentery always has been one of the most menacing, military disease problems both on account of the vast numbers of troops infected and the high death rate. It was the most frequently encountered disease transmitted by infected food and polluted water in the Middle East, the Pacific and South East Asia Commands (S.E.A.C.) in the Second World War. Marriott (1945) reported that the problem of diarrhoea and dysen­tery in South East Asia Command was second only to malaria. Human carriers and flies proved important factors in its dissemination. Fortunately, on all fronts the more serious Shiga dysentery infections were in a minority, generally not constituting more than 10 to 15 per cent of dysentery cases. The majority of infections were mild and were caused by organisms of the Flexner-Boyd group.

 

Professor E. K. Marshall, of Baltimore, and his team (1940) first described the chemical constitution and pharmacological properties of sulphaguani-dine, and as a result of extensive laboratory experimentations, suggested its use in bowel infections, including dysentery. Early in 1941, Professor Marshall sent 30 lbs. of sulphaguanidine to Lieut.-Colonel G. A. H. Buttle, in the Middle East. There Fairley and Boyd (1942) investigated its thera­peutic value, initially limiting observations to severe cases of bacillary dysentery where the causative organism had been isolated. Shiga infection was specially studied as this was the only type of dysentery liable to be fatal to troops. Prior to this, we had been investigating the value of a specially potent and concentrated anti-serum for Shiga dysentery with disappointing results. In vivid contrast to this, the therapeutic response to sulphaguanidine soon showed that the drug was a specific cure for Shiga dysentery as well as for dysenteries caused by the Flexner-Boyd group of B. dysenteriae. Owing to the necessity for identification of the organism in the initial series of cases investigated, it was generally necessary to with­hold treatment with the drug until the third or fourth day of the disease. As anticipated, later experience in New Guinea and elsewhere showed that the immediate administration of sulphaguanidine in full dosage within a few hours of onset of symptoms resulted in rapid cessation of the diarrhoea and radical cure. When given sufficiently early, the disease was practically aborted since multiplication of dysentery bacilli was terminated before the mucosa of the large bowel was seriously damaged. Convalescence was correspondingly shortened and the majority of infected troops were cured without needing to be evacuated from the forward areas. As a result of early sulphaguanidine treatment of all soldiers with diarrhoea in the forward areas in New Guinea, admissions to hospital were greatly reduced. The case mortality rate in the last 10,000 cases for diarrhoea and dysentery was 0.05 per cent.    

Even more dramatic evidence of its value from a military viewpoint was obtained during hard fighting over the Owen Stanley Ranges on the Kokoda trail in 1942, when a severe dysentery epidemic broke out in Australian troops. Japanese troops were at this time dying in considerable numbers from dysentery, and both forces had of necessity polluted the area in the immediate vicinity of the narrow mountainous jungle trail, along which successive advances and retreats were being made. As the epidemic pro­gressed in severity grave concern was felt regarding the ever-increasing number of dysentery casualities in the Australian Military Forces. At this juncture, Colonel E. Ford had all the available reserve of sulphaguanidine on the Mainland of Australia rushed by air to Moresby and transported to the forward area, where all troops with diarrhoea were immediately treated. At each Regimental Aid Post (R.A.P.) established along the trail at intervals of a few miles, sulphaguanidine in doses of 4 grammes (1 drachm) was administered to troops with diarrhoeal or dysenteric symptoms. The result was remarkable. Within ten days the epidemic was completely controlled, the incidence falling to the number of sporadic cases occurring before the epidemic. It was the considered opinion of many officers that sulphaguani­dine saved Moresby. 

As reported by Hill (1946) sulphaguanidine was later successfully used on a large scale in the South East Asia Command and became available in Burma in quantity in September, 1944. By October a significant fall in dysentery casualties had occurred, and by November the incidence had dropped to approximately 50 per cent. During the early summer of 1945, British and Indian troops were engaged in hard fighting on the plains of Central Burma. Hygienic standards had not appreciably changed, yet the incidence of diarrhoeal diseases remained at an unprecedented low level. In Brigadier Hill's opinion this lessened incidence was indisputably linked with the use of sulphaguanidine in the forward areas. Thus the results in Burma completely confirmed those obtaining in the South West Pacific. From a military viewpoint the outstanding merit of sulphaguanidine was its absolute safety for use by troops when not under medical supervision; for this reason it was particularly adapted for field use in the chemotherapeutic control of bicillary dysentery in jungle fighting, where a satisfactory standard of military hygiene and sanitation was difficult or impossible to attain. 

When conditions were static, adequate sanitation, sterilisation of water, screening of messes and kitchens, food protection, destruction of flies by D.D.T. and obliteration of their breeding places, resulted in the control and almost complete disappearance of bacillary dysentery in camps, cantonments and the like. The effects of residual spraying of kitchens, mess rooms and huts with D.D.T., in conjunction with the destruction of breeding places led to a great diminution in the fly population and often to their almost com­plete disappearance. 

Amoebic Dysentery

Amoebic dysentery was a more serious problem in South East Asia than in either the Middle East or the Pacific, both on account of its greater prevalence and the higher proportion of patients in whom radical cure proved difficult. Marriott (1945) reported that Entamoeba histolytica was isolated in 20 per cent, of the cases of diarrhoea in the South East Asia Command. Fairley and Boyd (1942) estimated the incidence of amoebic dysentery in the Middle East in 1941 was 12.3 per cent. In the South West Pacific, the incidence was definitely lower, the response to treatment satis­factory, and radical cure was never a problem—at least not in Australian troops. 

Hargreaves (1945) found that many individuals invalided to England in 1944 had been suffering from chronic amoebic dysentery' since 1942, having contracted the disease in the retreat from Burma at a time when anti-amoebic drugs were scarce and malaria and malnutrition rife. These intractable chronic amoebic patients who did not respond satisfactorily to treatment in India and Burma were later evacuated to Britain. Different factors which may have contributed to poor therapeutic response were a relative emetine-resistant strain of E. histolytica, repeated heavy infec­tions or ineffective early treatment due to the non-availability of emetine-bismuth-iodide (E.B.I.), which was in short supply in S.E.A.C.; on this latter account most soldiers in Burma received treatment with emetine hydrochloride injections which produce clinical but rarely radical cure in chronic infections. 

Hargreaves (1945) reached the conclusion that secondary bacterial infec­tions and not emetine fastness was the important factor in the production of chronic refractory patients returning to England from Burma and India, and considered that a course of penicillin and sulphasuxadine or sulpha­guanidine rendered these patients more amenable to specific treatment with emetine-bismuth-iodide. 

Typhus

Troops were affected with mite-typhus, flea-typhus and tick-typhus in tropical areas, but the only important and prevalent type both in New Guinea and the adjacent islands and in South East Asia Command, was mite-typhus. 

Mite-Typhus

The U.S.A. Typhus Commission reported that In both Burma and New Guinea rats were the chief natural hosts of Trombicula deliensis and Rickettsia. Mite-typhus, also known as scrub typhus, bush typhus, Japanese River fever, and tsutsugamushi disease, proved to be the only serious killing disease in the South West Pacific. It had an overall mortality of approxim­ately 9.0 per cent. Considerable variation in the mortality rate was found in affected troops in different geographical areas, the range varying from 0.0 to 30.0 per cent.   Considerable variations in the mortality rate were also found in South East Asia - due presumably to differences in the virulence of local strains. 

Control

Two measures for preventing or controlling mite-typhus developed during the war were (1) vaccination with killed Rickettsial sus­pensions, and (2) the application of miticides to the clothing. A large-scale controlled field experiment on the possible value of inoculation with scrub typhus vaccine from cotton-rats was being made in Burma when hostilities ceased; up to this time no definite conclusions had been reached regarding its efficacy in preventing mite-typhus or in lowering the mortality in inoculated troops contracting this disease. On the other hand, abundant evidence was available that the larval miticides—dimethyl and dibutyl phthalate—when properly applied to the clothing were effective in affording protection against mite-typhus. 

Dimethyl and Dibutyl Phthalate

The first demonstration of the effectiveness of dimethyl phthalate against mites was made in the United States. The Orlando group of entomologists found in 1942 that this compound was the best protective against mites; they also found dimethyl phthalate to be a very efficient repellent against culicine mosquitoes, whereas dibutyl phthalate was not so good. Madden, Lindquist and Knipling (1944) reported that pure liquid dimethyl phthalate applied to clothing gave complete protection against chigger mites up to 59 days. All other materials tested gave protection for much shorter periods. 

In 1942 other repellents were attracting more attention in U.S.A. than dimethyl phthalate. But as a mosquito repellent and miticide were urgently needed in the South West Pacific, and as dimethyl phthalate could be made in Australia, the Australian Mission in U.S.A advised the D.G.M.S. Australian Military Forces to adopt dimethyl phthalate for this dual purpose. Also about this time Australian Army entomologists com­menced their investigations on these substances. The effectiveness of dimethyl phthalate as a mosquito repellent against the Australian and New Guinea anopheline vectors of malaria was demonstrated. Major R. N. McCulloch, in an important series of experiments using human volun­teers, compared the action of D.D.T. dimethyl phthalate and dibultyl phthalate against larval mites in the field. While all three substances proved effective miticides, McCulloch proved that dibutyl phthalate was better retained in clothing, its miticidal action being preserved up to seven washings. The procedure advised was that one ounce of dibutyl phthalate be rubbed by hand into the woollen socks, canvas anklet or gaiters, cotton trousers and shirts once a fortnight. Volunteers, wearing clothing so treated with dibutyl phthalate, could spend hours in mite-infested jungle and lay down for two hours on more on mite-infested ground without showing a single bite from larval mites. 

Following universal treatment of clothing and blankets with dibutyl phthalate, a troublesome skin disease called scrub-itch caused by larval mite bites was rapidly controlled, while the incidence of scrub typhus was greatly diminished. Within one year of the introduction of dibutyl phthalate the typhus rate in New Guinea had fallen from 36 per 1,000 per annum to approximately 1 per 1,000 per annum. Indeed, where cases occurred, it was found either that there had been failure in delivery of supplies, or clothing was not being treated according to technical instructions. 

Later, Dr. Kenneth Mellanby visited Australia and New Guinea and methods of protection based on McCulloch's work with dibutyl phthalate were introduced into the South East Asia Command to protect troops against scrub typhus, with most gratifying results. Recently, Mellanby (1946) has reported that benyl benzoate may be even superior to dibutyl phthalate as a larval miticide. 

Louse-Typhus

Troops do not become lousy in the tropics and epidemic or louse-borne typhus played no part in any tropical campaign. D.D.T., however, was a most important discovery in regard to control of insect-borne disease in general, and passing reference must be made to its first large-scale use in controlling the typhus epidemic which broke out in Naples in December, 1943. Mass delousing was adopted by dusting clothing with 5 per cent D.D.T. powder. During January 1944 some 1,300,000 civilians were disinfected, and for the first time in medical history a typhus epidemic was terminated in mid-winter. 

D.D.T. (Dichlor-diphenyl-trichloTethane)

Few discoveries in the war have created greater interest or promised to be of more practical importance than the synthetic insecticide dichlor-diphenyl-trichlorethane or D.D.T. Though synthesised by a young German chemist, Zeidler, in 1874, it was not heard of again until it was resynthesised and its insecticidal powers discovered in the laboratories of the Swiss company of J. R. Geigy, in an intensive research directed by Lauger, Martin and Miiller (1944).   Patent rights were obtained in Switzerland in 1939. 

Swiss results in 1940 to 1941 had shown the great value of D.D.T. in controlling Colorado beetle in potatoes and other insect pests of plants, while its insecticidal properties against lice, fleas, mites, flies and mosquitoes were also investigated in 1941 to 1942. The startling effect of Neocid, a dust containing 5 per cent. D.D.T., against lice-infested clothes in the prevention of typhus fever was fully realised, and a ton of the substance was placed at the disposal of the Swiss Army. Most important work was carried out at the London School of Hygiene and Tropical Medicine by Buxton and his colleagues (1945) on its action on lice and general insecticidal properties. Similar valuable work was done by the Orlando group of entomologists in U.S.A. It was conclusively proved, largely as a result of extensive animal experiments in U.K. and U.S.A., that a 5 per cent solution in kerosene and a 10 per cent powder of D.D.T. are not dangerous to man provided precautions be taken. 

Subsequently, in South East Asia, in the Pacific, and in the Mediter­ranean area, the mosquito vector was controlled by applying a 5 per cent solution in oil to breeding areas to exterminate larvae, spraying swampy areas from aircraft and spraying houses by means of a flit gun or power sprayer with 5 per cent. D.D.T. in kerosene containing a small portion of pyrethrins. D.D.T. is slow in action, but if properly applied possesses a residual lethal effect lasting many weeks. It is a contact nerve poison, but as its action is slow it is advisable for house spraying to use it with a small proportion of pyrethrins to get an immediate “knock-down” effect. Recent work has shown that residual spraying of houses, barracks, troop ships, etc., is most effective in exterminating mosquitoes and flies. Similarly, the use of gas-operated sprayers, such as the aerosal bombs, proved of the greatest use in eliminating mosquitoes and other insects from fox holes, gun emplacements and dug-outs in the forward areas. The potential importance of D.D.T. as an Army insecticide is too well known to need further elaboration. It is sufficient to say that D.D.T. and other synthetic insecticides have brought much nearer the final control of many insect-borne tropical diseases. 

References

Field, J. W. (1939). Notes on the Chemotherapy of Malaria. Federated Malay States Govt. Press,   pp. 128-169.

Fairley, N. H. (1945). Chemotherapeutic suppression and prophylaxis in malaria.

Tram.Roy. Soc. Trop. Med.     Hyg., 38, 311.

Hill, T. R.   (1942).   Subtertian Malaria in War.   Ibid., 36, 75.

Curd, F. H. S., Davey. D. G., & Rose, F. L. (1945). Studies on Synthetic Anti­malarial Drugs. Some Biguanide Derivatives as New Types of Antimalarial Substances with both Therapeutic and Causal Prophylactic Activity. Ann. Trop. Med. & Parasit., 39, 218.

James. S. P. (1935). Consecutive Reports on the Antimalaria Chemotherapeutic Test carried out at the Devon Mental Hospital from 1932-1935.   pp. 1-14.

Maegraith, B. G., Adams, A. R. D., et al. (1945). Studies on Synthetic Anti­malarial Drugs. XIII. Results of a Preliminary Investigation of the Therapeutic Action of 4888 (Paludrine) on Acute Attacks of Benign Tertian Malaria. Arm. Trop. Med. & Parasit., 39, 225.

 

 

 

 

 

 

 

 

 

 

 

 

 

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Date: 1946 (required)
Main author(s): Sir Neil Hamilton Fairley (required)