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ENZOOTIC RODENT LEISHMANIASIS IN TRINIDAD, WEST INDIES’ Elisha S. Tikasingh, B.Sc., M.A., Ph.D.’ Human cutaneous leishmaniasis is a zoonotic drsease widely distributed in Central and South America. Small mammals play important roles in the natural history of the disease. This article attempts to define more precisely the roles that these mammals play in the ecology of the parasite. Introduction It is difficult to explain the sudden appear- ance of the disease after 1925 and its sudden Human cutaneous leishmaniasis is widely disappearance after 1930, but there may have distributed in several countries of Central and been significant reporting irregularities. South America. In recent years, workers in During studies on arboviruses, Worth, et al. Mexico, Belize, Panama, and Brazil have shown (24) observed lesions at the base of the tail in quite convincingly that the disease exists as a specimens of Marmosa spp., Heteromys anoma- zoonosis which only accidentally infects man lus and Zygodontomys brevicauda caught in with the parasite, and that wild animals (espe- Bush Bush Forest, Trinidad, and suggested that cially rodents) serve as the primary hosts. Three these lesions were similar to those caused by excellent papers have recently been published Leishmania mexicana in rodents of Belize (14). reviewing both the epidemiology in these coun- This was the first suggestion that rodent leish- tries (II) and taxonomic problems (12, 13). maniasis might be present in Trinidad. It was Although Ashcroft’s survey of helminthic not until 1968, however, that Tikasingh (IS) and protozoan infections of the West Indies (1) reported the presence of amastigotes in lesions does not mention the existence of leishmaniasis found on tails of the rice rat Oryzomys in Trinidad, the human disease seems to have laticeps3 and two murine opossums (Marnwsa been recognized there in the late 1920’s. The jkscata and M. mitis) captured in Turure . administrative reports of the Surgeon-General Forest. for Trinidad and Tobago covering that period The present status of the taxonomy of rice (16-22) cite the following hospital admissions rats is unsatisfactory. Among other things, the for cutaneous leishmaniasis: type previously referred to as Oryzomys laticeps at this laboratory has been identified Year No. of admissions by Dr. Guy Musser (American Museum of Natural History) as 0. capito velutinus. Thus, 1925. Not listed the report by Tikasingh (1.5) that Leishmania 1926 5 amastigotes were found in 0. laticeps (sub- 264 1927 sequently quoted by Lainson and Shaw-II) is 1928 184 incorrect, since the rodent was actually 0. 1929 Not listed 1930 136 capito velutinus. 1931 Not listed The discovery of Leishmania in Trinidadian rodents stimulated further study of the para- site’s ecology. This paper summarizes observa- tions along these lines that were made at ‘Also appearingin Spanishin Boletin de la Ojkina various localities. Particular emphasis was given Sanitaria Panamericana, Volume LXXVII, 1974. 2Senior Lecturer, Trinidad RegionalVirus Labora- tory, University of the West Indies. 3Actually 0. capito velutinus. 232 Tikmingh l RODENT LEISHMANIASIS IN TRINIDAD 233 PLATE l-Above: A clearing in the mora forest at Vega de Oropouche near the sandfly trapping station at VdO-2. Note the buttress of a mature mora tree and the large number of surrounding immature trees. Below: The secondary forest at Aripo-Waller Field, showing both timite (Manicaria saccifera) and tirite (Ix/znosiphon arouma) in the foreground. Timite, a palm, is found in the seasonal marsh forests of Trinidad and may grow to a height of seven meters. Tirite (Marantaceae), a herb, may grow up to three meters and commonly occurs in patches on the forest floor in wet forests. 234 PAHO BULLETIN * Vol. VIII, No. 3, 1974 to the Vega de Oropouche area, where the larger and more desirable mora trees were Leishmania work was combined with arbovirus removed by logging operations in the early studies. 1950’s; lumbering activities were again under- taken in May 1971 (see Plate 1). Field studies on Leishmania were carried out Materials and Methods at Vega de Oropouche from November 1969 Description of Areas Studied through September 1971 at two arbovirus stations (VdO-2 and VdO-3); the work was Vega de Oropouche. As shown in Figure 1, finally discontinued because of the lumbering this area is about 8 km northeast of Sangre operations. Grande, Trinidad’s fifth-largest town, and some Turure Forest. (See Figure 1.) This is an 4-6 km west of the sea. The land is roughly Evergreen Seasonal Marsh Forest in which the eight meters above sea level and is situated in an indicator species, “palma real” (Jessenia oligo- area of heavy rainfall which receives an average carpa) and timite (Manicaria saccifera) form a of over 255 cm of rain per year. The soil is secondary canopy at 3-9 meters. Because of sandy, so that drainage is not normally im- logging over the years, the upper canopy at peded, but many small temporary ground pools 18-24 meters is not as continuous as when it do form at the height of the rainy season. was studied by Beard (2) in the 1940’s. Poor The forest is classified as an Evergreen drainage and the existence of many depressions Seasonal Forest of the crappo-guatecare: mora result in a great deal of standing water during {Carapa-Eschweilera: Mora excelsa) type (2). the rainy season. Rainfall in this area averages There is a continuous canopy layer at 24-27 over 255 cm per year. meters, and the forest floor is dominated by Aripo- WaZZerField. (See Figure 1.) This area numerous seedling mora trees. According to is separated from Turure Forest by the Eastern Bell (3) the larger canopy trees lose all or Main Road, and is part of the Northern Plain of nearly all the leaves in their canopy branches, Trinidad. The area includes some unique an event which occurs mainly in April and stretches of Savannah that are of natural origin. October. As a result, there is a large quantity of As noted by Beard (2) the border areas of the leaf litter on the forest floor at these times. The savannahs contain palm-marsh merging FIGURE l-Map of Trinidad showing localities surveyedfor enzootic cutaneous leishmaniasis. The scale at upper left is in miles. N MILES dZ==TO i COLLECTING AREAS Tikusingh * RODENT LEISHMANIASIS IN TRINIDAD 235 “islands.” The vegetation of the marsh islands is for dermal glterations such as lesions and quite similar to that of Turure Forest. There are discrete swellings. When a lesion or swelling was large patches of tirite (Monotagma spicatum) found, a partial incision was made around it, on the forest floor. The mean annual rainfall the skin was folded back and an impression over a period of seven years at El Suzan Estate, smear was taken. The slide was then fixed with Cumuto, was 261.6 cm. Three stations (A2, A3, methanol and stained with Giemsa’s stain. and AlO) used in the arbovirus programme Microscopic examinations for Leishmania amas- (Tikasingh, in preparation) were utilized in the tigotes4 were made with a high-power (dry) work on leishmaniasis. objective and an oil-immersion objective. If no Santa Cruz. (See Figure 1.) Activities in the lesion or swelling were found the animal was Santa Cruz Valley were limited to an area near considered negative. Captured animals were Cantaro Village, just eight km northeast of the marked by toe-clipping and were released at the capital city of Port-of-Spain. The valley floor is site of capture. At Vega de Oropouche the planted mainly with citrus, cocoa and coffee, animals were usually released at weekly inter- but the hilly areas are covered by seasonal vals, while at other locations this was usually deciduous forest. The mean annual rainfall over done one to three days after capture. Pregnant 23 years of observation was 195.5 cm. animals were usually held at the laboratory for North Coast Road. This is essentially a hilly delivery of their litters and then returned to the area north of the Santa Cruz Valley, about 5 forest after their young were weaned. km along the North Coast Road (see Figure 1). Attempts were also made to culture the Its elevation of approximately 427 meters leishmania parasites in NNN medium. This was above sea level makes it the highest area done as follows: pieces of skin around a lesion surveyed. The forest is of the low montane type were finely triturated in 2.5 ml of a saline (2), with a closed canopy at 2 l-24 meters and solution containing antibiotics. As recom- no true lower stratum. Because of the hilly mended by Herrer, et al (7), the material was nature of the area, there are no water-logging placed in a refrigehtor for one or two days to operations. Rainfall is about 195 cm per reduce bacterial contamination, after which annum. 0.2-0.4 ml was used to inoculate the NNN Chaguaramas. (See Figure 1.) Chaguaramas is medium. Cultures were incubated in an air- located on the northwestern peninsula of the conditioned room and examined at 5, 10, and island. It is essentially a hilly area cut by four 30 days; if no promastigotes5 were seen after main valleys. The study sites were situated in 30 days the culture was considered negative and the valleys, most of which are dominated by discarded. It was also discarded (usually secondary forest; the exception is Tucker between five and ten days after inoculation) if Valley, where the forest is replaced by a large it were heavily contaminated with fungi. citrus estate. Rainfall is about 195 cm per year. When a strain of promastigotes was isolated, it was immediately inoculated into hamsters’ noses and occasionally into the dorsal portion Capture and Processing of Mammals of one or both hind feet.