Experimental Inoculation of Panamanian Mammals with Leishmania braziliensis

Abstract

Attempts to infect native Panamanian mammals with culture forms of local human strains of Leishmania braziliensis produced cutaneous infections for the first time in the spiny rat (Proechimys semispinosus), white-tailed tree rat (Tylomys panamensis), kinkajou (Potos flavus), and olingo (Bassaricyon gabbii). While infections of hamsters and cotton rats have usually lasted throughout the life of the animals, the parasites disappeared from the spiny rat and tree rat lesions within a month, but persisted in the kinkajous for at least 2 and 3 months. For a number of years we have attempted, at this laboratory, to infect native mammals with human strains of Leishmania braziliensis, sensu lato, in order to discover potential reservoir hosts of leishmaniasis. Early attempts here to infect wild mammals met with failure, but the routine inoculation of golden hamsters and occasional trials with cotton rats from our breeding colonies have shown that these rodents can be readily infected. Although cotton rats of the same species, Sigmodon hispidus, occur in Panama they are not primarily forest animals and so their susceptibility can have only limited significance in the epidemiology of this forest disease. The present paper reports the results of inoculation experiments conducted between June 1963 and September 1964. Lainson and Strangways-Dixon (1964) carried out inoculations of wild animals with Leishmania mexicana in British Honduras. They obtained infections in cotton rats, but of 41 specimens of other wild mammals, representing 11 species, only a single common opossum (Didelphis marsupialis) gave positive results. No lesion was produced at the site of inoculation and the infection was demonstrated only by culture from the liver. MATERIALS AND METHODS There is always the possibility that wild-caught mammals are already immune as a result of natural exposure in the forest. To avoid this difficulty, animals born or reared in the laboratory were used whenever available. In 1963 the breeding of the Received for publication 2 April 1965. * The work reported here was supported in part by a research grant (AI-01251) from the National Institute of Allergy and Infectious Diseases, NIH, USPHS. 842 arboreal white-tailed rat (Tylomys panamensis) was initiated at this laboratory. Although the average litter size was found to be only two, and the gestation period about 35 days, it has now been possible to build up the colony to about 130 individuals. Most of the Tylomys used in this study were laboratory-bred from wild-caught parents. The spiny rats (Proechimys semispinosus) were born in the laboratory from wild-caught gravid females. The woolly opossums (Caluromys derbianus) were laboratory-reared, but were brought into the animal room in the marsupia of wildcaught females. The cotton rats (Sigmodon hispidus) were from our colony established several years ago with stock from commercial sources in the U. S. The other animal species were wildcaught. Most of the live-trapped mammals were obtained near the town of Achiote, Province of Colon, Panama, where human cutaneous leishmaniasis has been known to be endemic for many years. The two strains of Leishmania used in the present study were isolated in Senekjie's modification of NNN culture medium from the cutaneous lesions of patients. The first of these isolates (Mstrain) was obtained in December 1960 from a patient having multiple lesions. The patient was a 48-year-old male who came to the laboratory for treatment. He had spent most of his life near Concepcion, in Chiriqui Province, but had developed the lesions while on the Changuinola River in Bocas del Toro Province, a known endemic area. The patient reported that the first lesion had started on the back of his hand in October 1960, and that about 3 weeks later others began to appear. When seen at the laboratory, the patient had an ulcer of from 1 to 3 cm in diameter in each of the following locations: hand, arm, tip of nose, thigh, neck, and left ear. This strain has been maintained in culture and in hamsters. The other strain used in this study (VH-strain) is of more recent origin. In April 1964 one of our fieldmen developed a large lesion on his upper left arm while engaged in trapping mammals in the Achiote area. This man has worked in the field for the Gorgas Memorial Laboratory for 28 years, and had been exposed in endemic areas many times w thout previously contracting leishmaniasis. Treatment was initiated as soon as the condition This content downloaded from 157.55.39.166 on Wed, 24 May 2017 20:53:57 UTC All use subject to http://about.jstor.org/terms THATCHER ET AL.-EXPERIMENTAL LEISHMANIASIS IN PANAMANIAN MAMMALS 843 TABLE I. Inoculations of Panamanian mammals with two human strains of L. braziliensis.