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Twenty-two black rats (Rattus rattus) were captured in houses where parasitologically confirmed cases of human visceral leishmaniasis had been recorded in Al-Arda Emara, Gizan province, south-west Saudi Arabia. Four of the rats were found to be infected with Leishmania; isoenzyme characterization showed that 3 were infected with L. donovani sensu lato zymodeme LON42 and the fourth with L. infantum zymodeme LON49. L. donovani s.l. LON42 has also been isolated from human visceral leishmaniasis patients living in this area, while dogs, but not humans, have been found to be infected with L. infantum LON49 in this part of Saudi Arabia.

Kala-azar (VL), mainly affecting infants and young children, is being increasingly reported in the south-west of Saudi Arabia, 305 cases being diagnosed in 1988. Most cases arise in scattered locations in the foothills west of the Asir mountains at altitudes between about 500 and 1000 m, although case clusters are apparent in some villages. Some cases also occur between the foothills and the Red Sea coast. The incidence in the south-west was calculated to be of the order of 6 to 8/10,000 population per year, but a random serological survey using the enzyme-linked immunosorbent assay and direct agglutination techniques indicated a seropositivity rate of about 3.7% in 706 apparently healthy children. Most patients are Saudi or Yemeni and cases are being increasingly identified also in the Yemen Arab Republic. In the foothills of both countries the causative organism is Leishmania donovani s.l. zymodeme LON-42, which also occurs on the eastern littoral of Ethiopia. By isoenzyme electrophoresis, it is readily separated from L. infantum, which has been identified in feral dogs, the 2 organisms being sympatric. The infection was found in 6.7% of 89 dogs, but their seropositivity rate was 19.3%. Although L. infantum has not yet been recognized in man in Saudi Arabia, it has been identified in a child in the coastal plain of the Yemen Arab Republic. Further research needed to provide a rational basis for control is discussed.

Cutaneous leishmaniasis (CL) is common on the high plateaux and foothills of the Asir range in the south-west of Saudi Arabia and Yemen. In 1987 1198 and 1104 cases were reported among the Saudi populations of Asir and Al-Baha provinces, representing an estimated annual incidence of 12 and 38 per 10,000 respectively. The incidence rises from October to December, then declines to a minimum between May and August. The prevalence of Phlebotomus sergenti, a proven local vector in the highlands, is roughly in inverse proportion. Cases occur at all ages, over 60% have only a single lesion, and the head and neck are most commonly affected. Apart from a few patients who develop leishmaniasis recidivans, most respond well to sodium stibogluconate, or self-heal. Of 44 isolates typed by isoenzyme electrophoresis, 42 were Leishmania tropica belonging to 5 distinctive zymodemes. LON-72 (34 isolates), LON-73 (1), LON-71 (2) and LON-10 (2) were found at altitudes around 2000 m, 3 of them in a single village. Three isolates of LON-63 were found at altitudes between 600 and 1000 m in widely separated foci. L. tropica LON-10 and LON-71 have been isolated also from P. sergenti from highland foci. LON-72 failed to produce lesions in BALB/c mice and gave rise to only transitory lesions in the footpads of hamsters.(ABSTRACT TRUNCATED AT 250 WORDS)