First recognized by ARAMCO health workers in 1948 [1], cutaneous leishmaniasis (CL) has been continually endemic in Al Hasa region, Eastern Province, Saudi Arabia. In the early 1990s CL was estimated to affect 2.8% of the population in Al Hasa [2]. Two leishmaniasis strains probably cause CL in Al Hasa, Leishmaniasis major and Leishmaniasis arabica.
Psammomys obesus is considered to be the reservoir host for both Leishmania species. Infections have also been found in another rodent, Meriones libycus, and in dogs [3]. The vector for CL in Al Hasa region is Phlebotomus papatasi [4]. Control of P. obesus and other rodents and P. papatasi began in 1988. From 1989 onward, the leishmania control program in Al Hasa has maintained continuous surveillance of CL and applied a variety of control measures. This report summarizes these eight years of CL surveillance data to assess the current epidemiology of the disease and effects of control measures.
We calculated CL incidence rates for each primary health care center (PHCC) catchment area for each year from 1989 to 1996. These rates and yearly changes in rates were compared to possible explanatory factors reflecting land use and intensity of control measures.
CL cases tended to cluster in eight of the 44 districts. This pattern of high incidence rates (84 to 374 per 10,000 per year) repeated in the same eight districts every year (Figure 1). The remainder of the districts consistently had low CL incidence rates that averaged under 20 per 10,000 per year. Districts with high CL incidence rates occurred throughout the farming areas of Hofuf. However, some low-incidence districts also were within the farming areas and one high-incidence district fell outside farming areas.
In 1989 control measures were first applied to 13 (30%) of the 44 Hofuf districts. CL incidence rates decreased by 35% from 1989 to 1990 (Figure 2). From 1990 to 1995, from 19 to 32 districts were covered by control measures. However, CL rates dropped an average of 10% per year during this period. Districts that at the beginning of the control program had higher CL incidence rates retained their rank as among the higher CL-infested districts throughout the period of CL control. Control measures were relaxed in 1995, and in 1996 CL cases increased by 25%.
Editorial note:
The wide variability in CL incidence rates within the relatively small geographic area of Hofuf suggests that CL transmission is highly focal. This pattern is consistent with short flight range of the vector and localization of the rodent hosts of this zoonotic disease. CL in humans does not fully reflect this localization because humans are far more mobile. Although many human probably become infected with CL in or around their home, others may become infected when visiting other districts for social or occupational activities. Inside districts of Hofuf the vector and rodent may also have limited distributions. We suspect that each district has a mix of highly localized environmental characteristics that determine CL incidence rates. Better clarification of this picture from CL surveillance will depend upon accurate localization of the homes and workplaces of persons with CL and careful histories of exposure in other districts.
Although CL surveillance data showed some impressive decreases in disease in the entire Al Hasa region, close inspection of the data showed no consistent effect. Districts that had control measures applied still maintained the highest incidence rates when compared with districts without control, and decreases in uncontrolled areas were no different from those in control areas. The rate of decrease in CL incidence was much lower from 1990 to 1995 than from 1989 to 1990 despite wider application of control measures. It is possible that there are complicated explanations for these inconsistencies with the hypothesis that the control measures reduce CL rates. However, the current surveillance data are insufficient to explore these possibilities. Improving the surveillance system is required to better identify CL transmission foci and to better assess the effect of control measures.
References
- Al-Dafas AA, Mohammed CK. The epidemiology of cutaneous leishmaniasis in ARAMCO health care population. In: Medical symposium on leishmaniasis, March 22-24, 1980, Dammam, Saudi Arabia; 147-160.
- Warrell DA. Leishmaniasis, malaria and schistosomiasis in Saudi Arabia. Saudi Med J 1993;14(3):203-20.
- Elbihari S, Kawasmeh ZE, Al-Naiem AH. Possible reservoir host(s) of zoonotic cutaneous leishmaniasis in Al-Hasse oasis, Saudi Arabia. Ann Trop Med Parasit 1984;78(5):543-5.
- Killick-Kendrick R, Leaney AJ, Peters W, Rioux JA, Bray RS. Zoonotic cutaneous leishmaniasis in Saudi Arabia. the incrimination of Phlebotomus papatasi as the vector in Al-Hasa oasis. Trans R Soc Trop Med Hyg 1985; 79:252-255.
