THE LEISHMANIAS, WITH SPECIAL REFERENCE TO THE ROLE OF ANIMAL RESERVOIRS

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1 AM. ZOOLOGIST, 5: (1965). THE LEISHMANIAS, WITH SPECIAL REFERENCE TO THE ROLE OF ANIMAL RESERVOIRS P. C. C. GARNHAM Dept. of Parasitology, London School of Hygiene and Tropical Medicine, England SYNOPSIS. Six varieties of Leishmaniasis are briefly described, namely, visceral leishmaniasis, oriental sore, Chiclero's ulcer, Panamanian cutaneous leishmaniasis, mucocutaneous leishmaniasis, and Uta. The natural foci of these diseases are described, and the evolution of each infection from its original location in the animal reservoir to total humanisation is followed. In the main, the wild canidae form the reservoir of the visceral diseases, and rodents of the cutaneous form. Many fallacies exist in the interpretation of what constitutes a zoonosis in leishmaniasis, and each situation must be looked at very carefully to ascertain the precise epidemiology. The control measures depend entirely upon a correct assessment of the position. The leishmaniasis scene is set in tropical and subtropical countries, and provides such a good example of a zoonosis and indeed of parasitological conditions in general, that the subject must prove of interest to all biologists and epidemiologists. In the broadest sense, a zoonosis means a disease of man acquired from animals. Probably all infections were at one time of this nature; some still are, like yellow fever; others scarcely have any link with animals, such as malaria. Leishmaniasis has reached a half way state, some forms being entirely zoonotic, others entirely human. I do not intend to describe in detail leishmaniasis and its causative organism, but it is necessary to stress that the disease is no more a single condition than trypanosomiasis or malaria, and there are at least six recognizable clinical and parasitological varieties. All are due to this paradoxical organism, Leishmania, which, though a flagellate, possesses no flagellum in the vertebrate host. VARIETIES The six varieties are as follows: 1) Visceral leishmaniasis or kala-azar, due to L. donovani. This insidious disease was not differentiated from malaria until the beginning of the century. It is a long illness, lasting a year or more, which always terminated in death until the specific cure, antimony, was discovered by Caspar Vianna in Brazil in There is a long continued fever, with splenomegaly and anemia, accompanied by a great fall in the polymorphonuclear leucocytes, so that resistance is lowered, septic conditions such as cancrum oris arise, and death follows. 2) Oriental sore or Borovsky's Disease, called after the Russian physician who first recognized the causative organism (L. tropica) in A papule develops at the site of the bite of the vector insect; this quickly ulcerates and lasts for a variable time. The so-called "wet form" is a florid lesion, causing extensive damage; the "dry form" is a more chronic condition. 3) Chiclero's ulcer, due to L. mexicana, and practically confined to the ear, which in the course of 30 or more years, gradually ulcerates away. 4) The Panamanian form of cutaneous leishmaniasis, which is a New World replica of Oriental sore. The geographical distribution of this parasite probably extends far beyond Panama; it may be present as far north as Costa Rica and southwards to Colombia, Venezuela, and the Guianas-in fact, to the historical "Kingdom of New Granada." The correct name of this parasite may be L. guyanensis. 5) Espundia or mucocutaneous leishmaniasis, due to L. braziliensis, which metastasises from the skin to the mucous membranes in 80% of cases. Hideous deformities of the nose and mouth are the result, and, because antimonial drugs are relatively inefficacious in this condition, death from secondary infections is frequent. (141)

2 142 P. C. C. GARNHAM 6) Uta, the Peruvian form of cutaneous leishmaniasis, due to L. peruvana, and without involvement of the mucous membranes. Excluded from this list are L. infantum, the cause of kala-azar around the Mediterranean, and L. pifanoi, the cause of "leishmaniasis diffusa" in Venezuela. The first of these varieties of leishmaniasis affects the viscera; the remaining five are confined to the skin or mucous membranes. It may be noted that all the latter conveniently possess geographical names. The causative organisms can best be distinguished by Adler's test (Adler, 1964). Leishmania belongs to the class Mastigophora, order Protomonadida, and family Trypanosomatidae. The adjacent family the Trichomonadidae consists largely of parasites of the intestine, like Trichomonas hominis; they have a simple life history. But Leishmania lives deep in the tissues and there is no direct connection between it and the outside world, so the life history must be more complicated, and a blood-sucking insect becomes necessary for transmission. Leishmania has, however, a simple structure and all the species are practically identical. They are oval, intracellular organisms, 2 or 3 /x, in length. The vesicular nucleus is central, while a rod shaped kinetoplast is placed at right angles to the main axis of the body. Sometimes a rhizoplast the origin of the flagellum may be seen arising from near the latter structure. As usual, the electron microscope reveals a much more complex picture; apart from the usual flagellar fibrils and centriole, there is a single enormous mitochondrion, which occupies most of the cytoplasm and contains a serrated bar the so-called kinetoplast (Garnham and Bird, 1962). The organism lives in the reticulo-endothelial system; a paradox, because such cells are the identical cells which phagocytose most protozoan parasites. In the cutaneous forms of the disease, the Leishmaniainfected cells accumulate in the subcutaneous tissue and at the growing margins of the ulcers; sometimes they creep into the more superficial tissues and may c\en be found in the stratum corneum. In visceral forms, the reticulo-endothelium is extensively parasitized in most organs such as spleen, liver, lungs, intestine and in the bone marrow. TRANSMISSION The infection passes from one vertebrate host to another by the bite of Phlebotomus, several species of which have been incriminated as vectors. Directly the insect has sucked up blood containing parasites, (derived either from the superficial layers of the skin or circulating in the blood stream), the leishmanias develop flagella and change into leptomonads. These multiply on the internal surface of the midgut by binary fission and gradually accumulate in enormous numbers in the mouth parts of the Phlebotomus. In a week, the insect is infective and will transmit the disease to another person or animal. NATURAL FOCI OF THE DISEASE Leishmaniasis presents the most interesting example of the uses of landscape epidemiology, as developed originally by the Russian school of Pavlovsky and quickly extended to other parts of the World (particularly to Poland and Czechoslovakia, and by Karl Meyer to California, Audy to Malaya, and Heisch to East Africa). This is an important branch of parasitology and involves taking a bird's eye view of the endemic locality. Of course, you start by examining the patients in hospitals or by surveying the general population, but you pay equal attention to the animals which may be natural reservoirs of the infection, to the trees, anthills, and burrows which shelter them, and to the arthropods which bite them. But you must also observe the food and habits of all these creatures, including man, as well as of the Phlebotomus larvae. Then rainfall, humidity, and winds must be assessed, until finally the time comes when you can enter a new country and see from a glance at the landscape where the danger lies, where infection is likely to be contracted, or where it can jjerhaps be guaranteed as absent. The zoonosis can exist only if suitable

3 THE LEISHMANIAS 143 FIG. 1. The Dynamics of Leishmaniasis or the Devolution of the Zoonosis. 1. Primary cycle between rodents and Phlebolomus. Accidental infection of man. 2. Intrusion of dogs into primary cycle. 3. Disappearance of primary reservoir and establishment of dog, Phlebotomus, man cycle. 4. Extinction of zoonosis and interhuman transmission by Phlebolomus. 5. The final picture: Complete humanization (by placental route) and disappearance of Phlebotospecies of Phlebotomus are present in the locality, and by suitable I mean species which will bite man as readily as the animal reservoirs; in other words, the vector must be both anthropo- and zoophilic. If the insect is solely zoophilic, it may be able to maintain the infection in the animal host, but Leishmania will be unable to reach man, as happens apparently in the town of Malakal in the Southern Sudan, where Hoogstraal and Dietlein (1964) found the infection to be present in the domestic rat (Rattus rattus) and a spiny mouse (Acomys sp.) but to be absent in man because of the absence of anthropophilic vectors. And, of course, all man- and animal-biting species of Phlebotomus may not be suitable hosts for the parasite. The role of animals in this disease is fundamental but often puzzling and fallacious. The two kinds of leishmaniasis, visceral and cutaneous, are associated with their own particular types of animal reservoir, kala-azar with jackals and foxes or other wild Canidae, and cutaneous leishmaniasis with a variety of wild rodents. This distinction is not absolute, and in tropical Africa rodents have been found infected with visceral strains. Curiously enough, the dog is later linked, as liaison carrier, with both forms of infection. The epidemiological pattern (Fig. 1) of leishmaniasis is a progressive one, on the same general lines as most zoonoses, at least those with a bacterial, viral, or protozoal etiology (see Garnham, 1959). At first, the infection is confined to the original wild animal host and its specific Phlebotomus vector; man is outside this cycle, but sooner or later, he intrudes into the feral environment, either sporadically as a hunter or more permanently in occupation of the terrain. In the sporadic instance, the zoonosis continues its old course, practically undisturbed, but in the permanent, the environment becomes profoundly changed; the wild animals are driven away, to be replaced by domestic animals and domiciliated vectors living in houses. It is now that dogs assume an important role, though the prevalence of canine leishmaniasis presents paradoxical features: in some highly endemic regions dogs are commonly infected; in others equally endemic, they seem to play no part. The infection may jump a step and be introduced directly into a town by a carrier, with the production of an urban epidemic, just as it occurs in the case of urban yellow fever. Sooner or later dogs disappear from the transmission scene, and even infection via the Phlebotomus ceases; humanization becomes so complete that air-borne, venereal, or transplacental infection replaces the natural route. Air-borne infection has long been suspected, i.e., by the Portuguese workers (Fraga da Azevedo, 1962). Its probabil-

4 144 P. C. C. GARNHAM ity has recently been confirmed by the NAMRU III team in the Sudan (Hoogstraal et al., 1963) which found the organism in the nasal mucus of 83% of cases of kala-azar, while Pessoa and Barretto (1944) noted that 80% of infections of L. braziliensis had nasal involvement. Cases of congenital infection are described from time to time, and, more recently in both England and Sweden, infection by blood transfusion has been noted (Barr et al., 1963). This is the final picture, which probably represents the extinction not only of the zoonosis but of the infection itself, because it is doubtful if the highly specialized Leishmania could long survive the absence of transmission via an invertebrate, although trypanosomes (e.g. T. equiperdum) sometimes succeed in doing so. The animal reservoirs of Leishmania are usually ideal hosts in that they provide highly infective cutaneous lesions containing organisms in the most superficial layers, organisms which are either harmless to the host or kill it only after many months have elapsed. I shall now try to illustrate this pattern of the evolving zoonosis in relation to specific instances. KALA-AZAR Middle Asia Perhaps the most pristine form of visceral leishmaniasis is seen today in Tajikistan, where Russian workers (i.e. Petrishcheva, 1961) demonstrated that jackals and wolves constitute a reservoir of infection for man; leishmaniasis runs a symptomless course in these animals and the zoonosis flourishes. In other parts of southwest Asia (e.g. Kirghiz), foxes are suspected of playing a similar part. Hoare (1962) pointed out that, with the gradual development of these territories, the wild Canidae are eliminated and dogs take their place; further afield as in Mediterranean countries all trace of a feral reservoir has disappeared. In the United Arab Republic, visceral leishmaniasis is apparently absent, because no suitable species of Phlebotomus is present there is only P. papatisi, which will not carry L. donovani. Tropical Africa Heisch and his co-workers ( ) spent many years trying to incriminate an animal reservoir in the semi-desert parts of Northern Kenya, where epidemics of kalaazar have raged in recent times. They approached the problem with great caution, discarding one apparent isolation from a mongoose and accepting their discovery of Leishmania in ground-squirrels and gerbils only as evidence of donovani-like parasites which were not necessarily concerned with the human disease. These workers demonstrated the existence of occult infections in three batches of spleens of gerbils (Tatera nigricauda) in the Rift Valley, and of a single batch of organs of gerbils from the Kitui district; they also found a similar inapparent infection in a ground squirrel (Xerus rutilus) captured in the Rift Valley. These isolations were the only successful results from the examination of many hundreds of animals, and the infection is obviously much less intense in Africa than elsewhere. It is difficult to visualize how such infected animals could be involved in transmission, and they probably represent a sterile by-product, or blind alley infections, for, apart from any other consideration, how could an occult infection in the spleen ever manage to infect Phlebotomus} These rodent strains proved to be avirulent, giving rise, on inoculation into man, to cutaneous lesions only, which nevertheless served to protect the individual against virulent strains of L. donovani (Manson-Bahr, 1963). The organism was thus thought to be L. donovani (or L. infantum) rather than L. tropica, and to have become attenuated by its accidental transfer to an abnormal rodent host. It may be quite fallacious, therefore, to regard these infections as part of a true zoonotic process. Neither dogs nor jackals seem to play any part in the epidemiology of kala-azar in East Africa, and it appears likely that in this region the infection is no longer a zoonosis but has reached the stage of interhuman transmission \ia the Phlebotomus (P. martini).

5 THE LEISHMANIAS 145 In the neighboring country Sudan Hoogstraal et al. (1963) adopted similar techniques and discovered Leishmania in four Arvicanthis niloticus, in one Acomys sp., in one genet and in one serval cat, but they found no infection in dogs. Kirk (1956) also failed to establish the presence of canine leishmaniasis in this region, although this British worker found a suspicious infection in one of four sand foxes (Vulpes pallida) within the Blue Nile endemic zone. Several members of the American team in the Sudan (Boyer, 1964) developed cutaneous leishmanial lesions which completely failed to visceralize, thus reacting like the volunteers in East Africa after inoculation with avirulent rodent strains of the parasites. It seems possible that L. donovani of zoonotic origin is feebly pathogenic to man (in Malta also this type of infection fails to spread beyond the lymph nodes), whereas after repeated interhuman transmission the virulence increases and the infection extends throughout the body. Such a tendency is noticeable also in borrelian, rickettsial and Pasteurella infections, and perhaps occurs in the cutaneous forms of leishmaniasis, where the non-zoonotic espundia is severe and the zoonotic chiclero's ulcer, etc., are mild in their manifestations; to attain full virulence, the organism has to become adapted to its new host by repeated interhuman transmission. The isolation of the organism by inoculation of emulsion of spleens from wild caught animals certainly proves the existence of the infection, but it may well be occult and inaccessible to the natural vector. I have inoculated a number of African small mammals with Sudanese strains of L. donovani, and recovered the organism only by a similar technique, i.e., from spleen; the parasite never seemed to reach the blood or skin. Thus, the infection in one out of two pygmy gerbils (Dipodyllus sp.), one out of five mongoose (Helogale sp.), and a jerboa followed this course. India In the preceding examples, kala-azar, if not a true zoonosis, is accompanied at least by infection in animals more or less closely linked with the human disease. In India, the great home of visceral leishmaniasis (though not necessarily its place of origin), the zoonosis aspect has apparently disintegrated completely; even the dog is no longer a host. This is the natural trend of any zoonosis (such as relapsing fever) which has become firmly established in epidemic form in man. Nevertheless, the freedom of Indian dogs from the infection is puzzling; kala-azar may be rife in the human population, transmission is affected by the common sandfly P. argentipes, and domestic dogs are numerous. Various explanations have been put forward, including the suggestion that this species of insect is unable to transmit by bite, but requires to be crushed, so that the leptomonads are set free to infect the wound; dogs are unable to crush the biting insect, and cannot contract the disease. A more likely explanation might be that P. argentipes is not attracted to dogs, but is entirely anthropophilic in its habits, although Lewis and Wharton (1963) found this species biting cows in Malaya. The absence of canine leishmaniasis in India has been confirmed by numerous surveys, but the absence of the infection in some remote wild animal is more doubtful, although in a densely populated country the original reservoir may well have disappeared long ago. Brazil The studies of the Deanes (1962) and Alencar (1961) clearly demonstrated that kala-azar is a zoonosis in some parts of Brazil (Ceara) at least; the former workers found a 12% and the latter a 4% infection rate in the fox, Lycalopex (Dusicyon) vetulus. Dermal infection is intense in these animals, particularly around the muzzle, which is avidly attacked by the local vector (P. longipalpis). The fox often comes close to human dwellings to raid chicken runs; the Phlebotomus get infected, and the organism is transmitted to domestic dogs or, rarely, to cats, or to man. The disease in the fox is quite severe, an indication that

6 146 P. C. C. GARNHAM this animal is not a true indigenous reservoir, and the zoonotic picture is therefore not as transparent as was at first thought. The fox does not exist in the Amazon Valley where sporadic cases of kala-azar were first noted 30 years ago, and in this region the true reservoir is probably yet to be found. Thus, in Brazil the zoonosis possibly proceeds as follows: the source is an unknown animal (perhaps a member of the wild Canidae); the infection infiltrated much later into the fox, Lycalopex vetulus, and at the same time into dogs; at the source, the infection in man is sporadic, but with the involvement of dogs and foxes it becomes at times epidemic and epizootic. The Brazilian investigators found that rates as high as 27% occurred in the dogs in certain loci. The fallacy here would be to regard the fox as the original source of the zoonosis. It seems, on the contrary, to be as much a liaison reservoir as the dog, and the situation is entirely different from that in Southern Russia. CUTANEOUS LEISHMANIASIS Cutaneous leishmaniasis presents even more curious features than does kala-azar, probably because it is less of a single entity; at least two forms occur in the Old World, and perhaps as many as five in the New World, all of which behave very differently as zoonoses. Middle East: Southern Russia The "wet form" of Oriental sore, due to L. tropica major, is probably the more primitive and flourishes as a typical zoonosis in Southern Russia and Iran. In Turkestan, the wild rodents (merions, Spermophillopsis leptodactylus) live in burrows in the steppes, together with vector species of Phlebotomies. Transmission proceeds so easily that 30% of the rodents may be found infected, and if man intrudes into this environment he may easily pick up the disease; as many as 70% of the population of new settlements in this region may acquire Oriental sore. A similar situation prevails in the neighboring territory of Iran in the gerbil Rhombomys optimus, as was demonstrated by Ansari and Faghih (1953), who found lesions on the nose and ears of 16% of these animals. Dogs are little concerned here, at least at first, because these regions are largely uninhabited by man or his domestic animals. A secondary reservoir in Russia is the hedgehog (Petrishcheva, 1963). In the towns, however, a second form of cutaneous leishmaniasis exists the dry form, due to L. tropica tropica (the socalled var. minor) and here the wild animal reservoir is replaced by the dog, which is said to show infection rates as high as 50% in Teheran, although Ansari (1956) was able to find the parasite in only 1% of dogs in the same city; much earlier, Wenyon (1911) completely failed to isolate Leishmania from over a hundred dogs in Baghdad where the human disease is so common. Probably the incidence of canine leishmaniasis fluctuates enormously, because other workers (e.g., Mills and Machattie, 1930) noted a high seasonal incidence of L. tropica in dogs in Baghdad, with lesions on the nose and on other areas uncovered by hair. In the United Arab Republic, there are endemic foci of Oriental sore in both Upper and Lower Egypt. Halawani (1940) found cases in the Delta, in the Iman El Shapai district of Cairo and around Assiut. The disease here may no longer be a zoonosis, as there are no records of infections in rodents or dogs. In the Mediterranean countries, Brumpt (1949) and later Fraga da Azevedo (1963) collected figures relating to the infection rates in dogs and found that they varied from 1 to 40%. It is probable that many of these records refer to visceral leishmaniasis (L. infantum) rather than to L. tropica. Cats and horses are occasionally found to have leishmanial lesions. Pakistan and Northern India Oriental sore is extremely common in Pakistan and Northern India, but the disease has practically ceased to be a zoonosis, and for some obscure reason the dog is rarely a reservoir here, however efficient it may be in the Middle East and around the Mediterranean Basin. There is a single rcc-

7 THE LEISHMANIAS 147 ord of a leishmanial lesion found by Sinton and Shortt (1934, 1938) on the nose of a dog at Karnal in the Punjab; it was successfully transmitted to Sinton himself and gave rise to a typical Oriental sore after a very long incubation period. An earlier record of canine leishmaniasis was made by Bahadur et al. (1925) in Bombay, where a pariah dog was found to have a superficial sore near the base of the ear. This form of cutaneous leishmaniasis has thus nearly reached the final degree of humanization, and revitalization from a feral source appears to be quite unnecessary. British Honduras and neighboring countries When Dr. Lewis and I (1959) visited the chicle forests of Central America, we were soon forced to the conclusion that chiclero's ulcer (due to L. mexicana) could exist only if the infection were a zoonosis; the workers in the forest are nomadic and sparse in distribution, and interhuman passage seemed to be utterly out of the question. We examined a variety of wild animals, including pacas, armadillos, and rodents, but without success, and it was not until three years later that Lainson and Strangways-Dixon (1963) proved that three species of sylvatic rodents were the reservoirs of infection. Lesions were present on 40% of Ototylomys phyllotis, 12% of Nyctomys sumichrasti and 10% of Heteromys desmarestianus. These animals are largely arboreal in habit, but descend to the ground at night, where they are readily bitten by the Phlebotomus vectors. Other local rodents, such as the cotton rat, can be easily infected experimentally, and there is little doubt that the range of natural reservoirs extends beyond the three which were incriminated in this investigation. In fact, Williams, Lewis and I (1964) found a fourth species (Tylomys) with a tail lesion when we returned to Central America in September, The chicleros and the Maya Indians keep large numbers of dogs in these forests; we examined the dogs for suspicious lesions, but failed to confirm the presence of the organism, so possibly the dog has no role to play in transmission in Central America. The disease is absolutely sylvatic; if dogs were involved, the infection might be expected to spread outside the forest, but this never occurs, not even into villages in clearings in the forest. I have recently inoculated two dogs with L. mexicana; one of them developed a scaly patch on the nose (the site of inoculation) in which scanty leishmania were found. The other developed a large swelling in which the organisms were numerous. Hence, the dog is susceptible to this strain, even though mildly. The animal reservoir must therefore be a strict forest dweller and once the sylvatic environment is disturbed, the rodents leave and the infection dies out. Probably for this reason, L. mexicana is confined to these few forests of Guatemala, Yucatan, and British Honduras; further South, where the forest is replaced by cultivation, as in Honduras and Costa Rica, another form of the disease appears instead. In Central America, the zoonosis probably dates at least from the decline of the old Maya civilization, a thousand years ago, when the heavily populated country became overgrown with forest and the right conditions were established. Panama A most peculiar situation prevails in this country, where leishmaniasis has been studied by workers at the Gorgas Memorial Laboratory for some years. In 1958, Hertig et al. reported the presence of a 10% infection rate in the heart blood of spiny rats (Proechimys semispinosus and Hoplomys sp.); the parasite was absent in the tissues of the animals and in subinoculated hamsters, but it gave rise to lesions in human volunteers. In subsequent years, the infection could no longer be found in the rodents, yet men who go into the forests of Panama frequently contract the disease, while MacConnell demonstrated natural infection in Phlebotomus caught in the forest. Adler has shown serologically that the Panama strain of parasite is close to L. mexicana; the vectors are probably the same as those occurring further north, and, although the

8 148 P. C. C. GARNHAM disease is clinically different in the two regions in man and hamsters, the two strains are undoubtedly closely related. Probably arboreal rodents are the true reservoirs in Panama, as they are in British Honduras. The infections in Proechimys may therefore have represented a false clue, and are perhaps "dead ends" like those in the gerbils and squirrels of East Africa. Recent work by my student, Jeffrey Shaw (1963), showed that the sloth in Panama harbors a flagellate, Endotrypanum schaudinni, which is closely related to Leishmania. It apparently develops in Phlebotomus, gives rise to leptomonads and not crithidias in culture, and is serologically very similar to Leishmania. Moreover, Deane (1961) found Leishmania in the spleen of sloths in Brazil. The researches are incomplete as yet, and it would be premature to speculate on the part played by the sloth, if any, in the epidemiology of the human disease. Brazil This country is the great home of muco cutaneous leishmaniasis or espundia, and the disease has been extensively studied in the various states. Neither the clinical nor the epidemiological pattern of the disease is uniform, and in a recent survey by Heisch (1963) at least four geographical types were distinguished. My limited knowledge is confined to the classical form, in which Brazilian workers minimize the importance of an animal reservoir, particularly when the disease is occurring in almost epidemic fashion in newly developed regions, as in the states of Sao Paulo, Matto Grosso and Minas Gerais. However, it was in circumstances such as these that Pessoa (1963) stressed the potential danger of entry into a natural focus of the disease, e.g., the construction of the new capital or the North- South Highway. Other population movements may be accompanied by epidemics, and de Carneri et al. (1963) describe an interesting focus of the disease on the Xingu River, a tributary of the Amazon, north of Brasilia. The Indians were driven by enemy tribes into uninhabited forest, where they quickly contracted cutaneous leishmaniasis, almost certainly of zoonotic origin. In Brazil, dogs are rarely affected; in the Matto Grosso, Forrattini and Santos (1955) found only one infected dog out of 180 examined. Leishmaniasis is equally uncommon in wild animals, although the latter authors noted rare infections in a paca, an aguti, and in Kannabatsomys amblyonyx. Probably a survey of wild rodents would reveal the existence of a sylvatic reservoir in these forests of Southern Brazil. Further north, near Fortaleza, Alencar et al. (1960) isolated the organism from a domestic rat (Rattus r. alexandrinus). As in other parts of the New World, the cutaneous form of the disease is closely linked with tropical rain forest, and it is here that the reservoir must be sought; infected rodents (Oryzomys) have now been fund in Amazonia (Guimaraes, 1964). On the other hand, L. donovani is prevalent in trie foothills and valleys of much drier country with a different zoonotic background and vectors. Heisch (1963) pointed out that in the relatively open country of East Brazil there may be overlapping in the distribution of cutaneous and visceral leishmaniasis. Thus in the main espundia areas, the disease seems to be progressing to the epidemiological form characteristic of India, with the disappearance of the zoonosis. Peru On the Pacific slopes of the Andes occurs a specialized type of cutaneous leishmaniasis known as "uta," which presents a situation totally unlike that seen elsewhere in the New World, as emphasized by Pifano (1960). In contrast to the conditions prevailing in most other Latin American countries, dogs are commonly affected and surveys made by Herrer and other Peruvian workers (1951) have demonstrated infection rates varying from 10% to over 50%. The dogs were often without visible ulcers, but the organisms could be readily found in the skin, especially in the nasal region. Herrer was able to reduce the incidence to less than 2" c by peridomestic spraying with

9 THE LEISHMANIAS 149 TABLE 1. Animal reservoirs of leishmaniasis. Species Country Primary reservoir Secondary reservoir Dogs L. donovani U.S.S.R. Jackals, wolves, foxes L. tropica L. braziliensis L. peruana L. guyanensis L. mexicana Mediterranean India, Pakistan Kenya Sudan Brazil U.S.S.R., Persia Mediterranean India, Pakistan Brazil Peru Panama Guatemala, British Honduras & Mexico DDT. On the other hand, the infection could not be found in a wide range of wild mammals. It is hardly surprising that cutaneous leishmaniasis should have a different epidemiology in Peru, where transmission takes place in caves in the barren Cordilleras as high as 2,800 metres, entirely different from the Amazonian jungle or tropical rain forest. CONCLUSION I should like to stress the need for caution in the interpretation of what constitutes a zoonosis in leishmaniasis. There is little doubt that the burrow dwelling gerbils of Middle Asia or the arboreal rodents of Central America are the original vertebrate hosts of the organism, and that dogs in Peru or around the Mediterranean Sea are important secondary reservoirs. But the presence of occult infections in various wild animals, in Africa or in the New World, and even the high infection rates in the blood of spiny rats in Panama, do not necessarily signify the existence of a zoonosis. The existence of Leishmania in wild animals may represent merely a secondary zoonosis, as in the foxes of Brazil or the bears of Kurdistan. It is important to ascertain the precise situation, because control of the human disease depends upon a correct assessment of the zoonosis. If a true primitive zoonosis exists, the infection is likely to be difficult Arvicanthus, Acomys Merions, gerbils Rodents (Oryzomys) Arboreal rodents Ground squirrels & gerbils Carnivores Fox + Hedgehog, etc. + (Paca, aguti) Spiny rat Rare to eradicate; if the zoonosis is more apparent than real, it would be wasted effort to exterminate the fallacious reservoirs. Protection of the human community may be possible by using poison in the localized habitat of the gerbil reservoirs, as was done so successfully in Turkestan; in tropical rain forests, such measures would be impracticable. Where canine leishmaniasis is a problem, as in China or Ceara, the infection can be diagnosed and the diseased dogs can be treated or destroyed. When the disease is entirely sylvatic, neither an attack on the feral reservoir nor the eradication of the non-domestic vector is practicable, and it is necessary to resort to protective vaccination. Table 1 provides a summary of the part thought to be played by animals in the epidemiology of the different forms of leishmaniasis. REFERENCES Adler, S Leishmania. In Advances in Parasitology, p , B. E. Dawes [ed.], Academic Press, London & New York. Alencar, J. E., E. P. Pessoa, and Z. F. Fontanele Infeccjio natural de Rattus ratlus alexandrinus por Leishmania (provavelmente L. braziliensis) em zona endemica de leishmaniose tegumentar do estado de Ceara, Brasil. Rev. Inst. Med. Trop. Sao Paulo 2: Ansari, N., and M. Faghih Leishmaniose cutanee a L. tropica chez Rhombomys opimus. Ann. Parasitol. 28: Bahadur, K., C. R. Avari, and F. F. Mackie Canine leishmaniasis in Bombay. J. Trop. Med. Hyg. 28:84.

10 150 P. C. C. GARNHAM Barr, M., E. Bengtsson, P. C. C. Garnham, G. Hult, and R. Kostmann Kala-azar transferred by exchange blood transfusion in two Swedish infants. Proc. VII Internat. Congr. Trop. Med. Malar. (In press) Borovsky, P. F On sart sore. Translated and edited by C. A. Hoare. Trans. Roy. Soc. Trop. Med. Hyg. 1938, 32: Boyer, J. H Personal communication. Brumpt, E Precis de Parasitologie I. Masson, Paris. Deane, L. M., and M. P. Deane Visceral leishmaniasis in Brazil: Geographical distribution and transmission. Rev. Inst. Med. Trop. Sao Paulo 4: Deane, L. M Tripanosomfdes de mamiferos de Regiao Ama/onica. I. Alguns flagelados encontrados no sangue de mamiferos silvestres do Estado do Para. Rev. Inst. Med. Trop. Sao Paulo 3: De Carneri, I., N. Nuttels, and J. A. Miranda Epidemic of South American leishmaniasis among the Waura Indians of the Xingu National Park. Rev. Inst. Med. Trop. Sao Paulo 5: Forattini, O. P., and M. R. Dos Santos Nota sabre um foco de leishmaniose tegumentar americana no estado de Mato Grosso, Brasil. Rev. Bras. Malar. 8: Fraga da Azevedo, J Biologia da Leishmania donovani em relacao com a sua accao patogenica e a epidemiologia do kala-azar. Riv. Iber. Parasitol. 22:3-48. Fraga da Azevedo, J Rapporti fra la leishmaniosi canina e la leislimaniosi umana in Portogallo. Arch. Ital. Sci. Med. Trop. Parassit. 44: Garnham, P. C. C The evolution of the /oonoses. Med. Press 242: Garnham, P. C. C, and D. J. Lewis Parasites of British Honduras with special reference to leishmaniasis. Trans. Roy. Soc. Trop. Med. Hyg. 53: Garnham, P. C. C, and R. G. Bird A preliminary study of the fine structure of Leishmania mexicana as seen under the electron microscope. Sci. Repts. 1st. Super. Sanita 2: Guimaraes, F. X "Or\7oni)s goeldi" a wild rat from Amazonia as resenoir of "Leishmania brasiliensis." 1st Internat. Congr. Parasitol. Rome (In press). Halawani, A On the distribution of oriental sore in Egypt. J. Egypt. Med. Assoc. 23: Heisch, R. B Studies in leishmaniasis in East Africa. I. The epidemiology of an outbreak of kala-a/ar in Kenya. Trans. Ro). Soc. Trop. Med. Hyg. 48: Heisch, R. B The isolation of Leishmania from a ground squirrel in Kenya. East Atr. Med. J. 34:1 S3. Heisch, R. B., \\\ F. Grainj-ei. and A. F. C. Hand, l'.tj'.l. I he isolation ol a I ci^limamn finm geil):k in Kenya. J. Trop. Med. Hyg. 62: Herrer, A., and M. G. Battistini Estudios sobre tegumentaria en el Peru. I. "Infecci6n experimental del perro con cepas de Leishmanias procedentes de casos de uta." Rev. Med. Exper. 8:9-27. Herrer, A Estudios sobre tegumentaria en el Peru. II. "Infecci6n experimental de zorros con cultivos de leishmanias aisladas de casos de uta." Rev. Med. Exper. 8: Herrer, A., and M. G. Battistini Estudios sobre tegumentaria en el Peru. III. "Reproduccion experimental de la uta en el hombre." Rev. Med. Exper. 8: Herrer, A Estudios sobre tegumentaria en el Peru. IV. "Observaciones epidemiologicas sobre la uta." Rev. Med. Exper. 8: Herrer, A Estudios sobre tegumentaria en el Peru. V. "Leishmaniasis natural en perros procedentes de localidades ut6genas." Rev. Med. Exper. 8: Hertig, M., G. B. Fairchild, and C. M. Johnson Ann. Rep. for 1957, Gorgas Mem. Lab. Hoare, C. A Reservoir hosts and natural foci of human protozoal infections. Acta Trop. 19: Hoogstraal, H., D. Heyneman, D. R. Dietlein, H. G. Browne, T. P. Reid, P. F. D. Van Peenen, A. H. Saber, and L. C. Rohrs Leishmaniasis in the Sudan Republic: Epidemiological findings. Bull. Wld. Hlth. Org. 28: Hoogstraal, H., and D. R. Dietlein Leishmaniasis in the Sudan Republic; Recent results. Bull. Wld. Hlth. Org. 30: Kirk, R Studies in leishmaniasis in the Anglo-Egyptian Sudan. XII. Attempts to find a reservoir host. Trans. Roy. Soc. Trop. Med. Hyg. 50: Lainson, R., and J. Strangways-Dixon Dermal leishmaniasis in British Honduras. Trans. Roy. Soc. Trop. Med. Hyg. 57: Lewis, D. J., and R. H. Wharton Some Malayan sandflies (Diptera: Psychodidae). Proc. Roy. Entomol. Soc. (London), B, 32: Manson-Bahr, P. E. C Active immunization in leishmaniasis. p In P. C. C. Garnham, A. E. Pierce, and I. Roitt, feds.), Immunity to protozoa. Blackwell Scientific Publications, Oxford. McGonnell, E Leptomonads of wild-caught Panamanian Phlebotomtis: Culture and animal inoculation. Exptl. Parasitol. 14: Mills, E. A., and C. Machattie A preliminary note on the relationship of the parasites of human and canine dermal leishmaniasis. Trans. Roy. Soc. Trop. Med. Hyg. 23: Pa\lovsky, E. N. I'ndated. Human diseases with natural foci. Foreign Languages Publishing House, Moscow. PciMia. S. B., and M. P. Barretto I.eishmanime trgiimeutdr americana. Sao Paulo Min. Educ N.tilde*. l'cssoa, S. B Endemicas parasitarias da 7ona

11 THE LEISHMANIAS 151 rural Brasiliera. Sao Paulo, Procienx. Petrishche\a, P. A Methods of study and prophylaxis of leishmanial and mosquito borne fevers. Medgiz, Moscow. Petrishcheva, P. A Leishmaniosis na USSR e sua profilaxia. Proc. 7th Internat. Congr. Trop. Med. Malaria (In press). Pifano, C. F Algunos aspectos de la patologia coraparada geografica de la leishmaniasis tegumentaria en el tropica Americano. Gac. Med. Caracas 68: Shaw, J. J., and A. Voller Preliminary fluorescent antibody studies on Endotrypanum schaudinni. Demonstration at laboratory meeting. Trans. Roy. Soc. Trop. Med. Hyg. 57: Sinton, J. A., and H. E. Shortt Cutaneous leishmaniasis as a natural infection of a dog in India. Ind. J. Med. Res. 22: Sinton.. A The successful transmission of cutaneous leishmaniasis by inoculation to man from a natural lesion occurring on a dog in India. Ind. J. Med. Res. 25: Vianna, G Tratamento da leishmaniose tegumentar por injeccpes intravenosas de tartaro emetico. An. 7 Congr. Bras. Med. Cirurg. 4(3): Wen yon, C. M Oriental sore in Baghdad together with observations on a gregarine in Slegomyia fasciata, the haemogregarine of dogs and the flagellates of house flies. Parasitology 4: Williams, P., D. J. Lewis, and P. C. C. Garnham On dermal leishmaniasis in British Honduras. Trans. Roy. Soc. Trop. Med. Hyg. (In press).

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