Mixed leishmanial infections in Rhombomys opimus: a key to the persistence of Leishmania major from one transmission season to the next.

An important feature of the foci of zoonotic cutaneous leishmaniasis (ZCL) in Turkmenistan and Uzbekistan is a 6-10-month break in transmission when Leishmania parasites persist in great gerbils (Rhombomys opimus)--the main host for three species (L. major, L. turanica and L. gerbilli). Almost all (95%) of the laboratory-maintained R. opimus experimentally infected with L. major cured their infections within 6 months, a situation which, if mirrored in field conditions, cannot provide reliable persistence of the infection to the next transmission season. However, infections with L. turanica alone persisted for a mean of 15 months, and mixed infections of L. major and L. turanica persisted even longer (mean = 25 months), parasites of both species remaining detectable in the skin for at least 18 months. Isoenzyme identification of 664 isolates obtained from wild-caught R. opimus, and of 58 cloned strains developed from them, showed that L. turanica, which is non-pathogenic for humans, tends to predominate in the gerbils from all types of natural ZCL foci, including those which are hyper-endemic; in June, L. turanica may be present in 80%-100% of the R. opimus in the foci. In contrast, infections with L. major alone occur far less commonly, and are especially hard to find at the beginning of the transmission season. However, 5%-25% of great gerbils in these foci are each infected with a mixture of L. major and L. turanica. In hyper- and meso-endemic foci, the proportion of L. major within mixed infections of Leishmania increases significantly towards the end of transmission season (August-September). It would appear, therefore, that mixed L. major/L. turanica infections in R. opimus promote the persistence of L. major between transmission seasons.

[The isoenzyme identification of Leishmania isolates taken from greater gerbils, sandflies and human patients in foci of zoonotic cutaneous leishmaniasis in Turkmenistan]. / Izoénzimnaia identifikatsiia izoliatov leishmanii, vydelennykh ot bol'shikh peschanok, moskitov i bol'nykh liudei v ochagakh zoonoznogo kozhnogo leishmanioza v Turkmenistane.

In 1991-1992, 230 isolates were obtained in the Tedzhen oasis and its adjacent desert areas: 172 isolates from great gerbils, 39 from P. papatasi, and 19 from human cutaneous leishmaniasis patients. All the isolates were identified by the isoenzyme polyacrylamide gel electrophoresis by 8 enzymes. The characteristics of Leishmania circulation in the hyperendemic foci of Turkmenistan were similar to those previously studied in the mesoendemic areas of Uzbekistan and Kazakhstan. L. turanica which is non-pathogenic for man prevailed among infected great gerbils in winter, spring, and early summer, making the natural foci epidemiologically safe in that period of time. It was only in August-September that the great gerbil infection rate by L. major appeared to increase, occasionally reaching 100%. Epizootics due to L. major are developing in the presence of L. turanica, therefore most isolates are clone mixtures of L. major and L. turanica. P. papatasi is the only vector in the Tedzhen oasis; there has been strong evidence for its transmission of both L. major and L. turanica, which makes the concept inconsistent that P. papatasi is associated only with L. major. The overall analysis of recent findings of the distribution of L. major in the populations of great gerbils makes it possible to limit the former endemic zoonotic cutaneous leishmaniasis areas to 40 degrees N latitude and the southern borders of Turkmenistan and Uzbekistan. Within this area, the distribution of L. major is uneven and associated basically with rivers, valleys, oases, and foothill desert plains.

[The characteristics of the epidemic activation of a natural focus of zoonotic cutaneous leishmaniasis in places with a sympatric dissemination of Leishmania major, L. turanica and L. gerbilli]. / Osobennosti épidemicheskoi aktivizatsii prirodnogo ochaga zoonoznogo kozhnogo leishmanioza v mestakh simpatrichnogo rasprostraneniia Leishmania major, L. turanica i L. gerbilli.

In 1975-1978 and in 1985-1988 studies of species composition and number of Phlebotomus, R. opimus infestation with L. major, L. turanica and L. gerbilli as well as epidemic activity of the natural foci were performed in the Karshi steppe in Uzbekistan. Typical areas have been compared in the desert, oasis and desert land irrigated for cotton growing. A correlation has been established between the epidemic activity of the natural focus and the nature of epizootic development in R. opimus and species composition of vectors. On desert territories epizootic transmission throughout the whole season develops with the domination of one leishmania species (L. turanica) which is not pathogenic for human beings. Paraphlebotomus are the main vectors transmitting leishmania. In oases epizootic process assumes a two-phase course, with accumulation by the middle of the season L. major species pathogenic for human beings. It is transmitted by P. papatasi. With desert irrigation, the former Phlebotomus species is transformed into the latter one, with the predominance of P. papatasi. Epizootics acquire a stable two-phase nature.

A new species of Leishmania isolated from the great gerbil Rhombomys opimus.

Leishmania turanica n.sp., found infecting the desert rodent Rhombomys opimus in the southern territories of the USSR and the Mongolian People's Republic, is described. This parasite exists sympatrically with L. major and L. gerbilli in R. opimus and is the predominant species. A total of 284 isolates of L. turanica from R. opimus, 3 from naturally infected Phlebotomus andrejevi and 1 from P. papatasi were characterized and found to be clearly distinguishable on isoenzyme and nuclear DNA characteristics from all other Old World taxa of Leishmania.

[The isoenzyme identification and pathogenic characteristics of the Leishmania isolated in natural foci of cutaneous leishmaniasis in the USSR]. / Izoénzimnaia identifikatsiia i patogennaia kharakteristika leishmanii, vydelennykh v prirodnykh ochagakh kozhnogo leishmanioza v SSSR.

By 8-11 enzymes, using polyacrylamide gel electrophoresis, 378 isolates from R. opimus, 3 isolates from M. libycus, 4 isolates from P. andrejevi, 1 isolate from P. papatasi, 1 isolate from S. murgabiensis and 25 isolates from human patients with skin leishmaniasis have been identified. Using starch gel electrophoresis, 17 strains from R. opimus and 3 strains from patients have been additionally identified by 12 enzymes. All the isolates were tested for ability to cause leishmaniasis disturbances in golden hamsters intracutaneously injected into the ear. It is established that L. major is a polytypic group which on the territory of the USSR consists of 3 independent species: L. major (in a narrower sense), L. gerbilli and L. sp. nov, a new earlier unknown species. All three types of Leishmania are specific parasites of R. opimus and only L. major may affect man and M. libycus. 3 types of Leishmania may coexist in the body of one animal. In R. opimus and golden hamsters, all of them caused only skin damages, visceralization was never registered. In golden hamsters, L. major always caused progressing ulcers, while L. sp. nov. and L. gerbilli caused only infiltrative damages. Only 9 (3%) of 268 L. sp. nov. isolates caused ulcers developing similar to those caused by L. major in the experimental animals. The data obtained account for the local nature and seasonal regularities of the epidemic process in the natural foci of skin leishmaniasis by the changing proportion of L. major in the complex of Leishmania encountered in R. opimus.

[Effect of the irrigation and reclamation transformation of the Karshi Steppe on burrow sandflies of the genus Phlebotomus--vectors of the causative agent of zoonotic cutaneous leishmaniasis]. / Vliianie irrigatsionno-meliorativnogo preobrazovaniia Karshinskoi stepi na norovykh moskitov roda Phlebotomus--perenoschikov vozbuditelia zoonoznogo kozhnogo leishmanioza.

Studies of land irrigation effect on Phlebotomus sandflies, carriers of Leishmania major (a zoonotic cutaneous leishmaniasis causative agent)--were performed for 15 field work periods, from 1967 to 1981, at 18 sites in various natural areas of the Karshi Steppe (Uzbek SSR). Over 43500 sandfly specimen were caught and identified. Regularities in sandfly number changes, first of all, that of Ph. papatasi, after irrigation were determined, with respect to various proximity of great gerbils' settlements, where sandflies breed in the irrigated fields. Well-drained sites situated higher than irrigated fields are practically unaffected by irrigation, sandflies number and specific composition being practically unchanged. At the sites situated either on the same level with irrigated fields or 3-5 m lower the number of sandflies changes usually in 2 stages: 1) short-term increase in Ph. papatasi number at the very beginning of the irrigation period; 2) formation of stably high or low Phlebotomus numbers due to stabilization of hydrothermal regime in the holes of great gerbils.