Geographical distribution and epidemiology of Visceral leishmaniasis

• Geographical distribution and epidemiology
• Foci of old world Visceral leishmaniasis
• Foci of new world Visceral leishmaniasis

Kala azar distribution maps

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Visceral leishmaniasis is endemic in the tropical and sub-tropical regions of Africa, Asia, the Mediterranean, Southern Europe, South and Central America. The distribution of VL in these areas however is not uniform, it is patchy and often associated with areas of drought, famine and densely populated villages with little or no sanitation. In endemic areas children below the age of 15 are commonly affected. In sporadic and epidemic cases of VL people of all ages are susceptible with males at least twice as likely to contract the disease than females, except those who have conferred immunity due to past infection (WHO expert committee report, 1991; Rab et al, 1995). In Pakistan 239 cases of VL due L.d infantum were reported between 1985 and 1995, of these 52% were children below the age of 2 years, 86% were children below the age of 5 years, this represented an increase of ten-fold in infantile VL cases over the 10 year period from 0.2 to 2 per 100 000 population and male cases out numbered female cases by three times (Rab et al, 1995). Visceral leishmaniasis has been known to exist in the Himalayas in Pakistan for over three decades. However recently sporadic cases are beginning to appear in the North West Frontier Province (NWFP), Punjab and Azad Jammu and Kashmir (AJK). All of these areas are mountainous and contain large farming communities (Rab et al, 1995). In neighbouring India VL is endemic in the states of Bihar, Uttar Pradesh and West Bengal. One of the largest epidemics occurred in 1978 in North Bihar where over half a million people fell victim to VL. In the first eight months of 1982, 7500 cases were reported in India and in one year alone between 1987 and 1988, 22 000 cases of VL were registered (WHO expert committee report, 1991). In Bangladesh cases of VL greatly declined between 1953-1970, probably as a result of mass chemotherapy with pentavalent antimonials and wide spread spraying with DDT to control malaria. Following the end of the malaria control programme in 1970, sandfly vector populations increased and so did the cases of VL and currently appear at a rate in excess of 15000 per year (Al-Masum et al, 1995). In Brazil, VL is distributed widely in the south, east and the central regions of the country. Visceral leishmaniasis commonly affects poor and malnurished children below the age of 15 years (Arias et al, 1996). The disease is highly endemic in the states of Bahia and Ceara, which together account for 70% of the total cases of VL in Brazil (WHO expert committee report,1991). Upto 1989, 15000 cases of VL had been recorded in the states of Alagoas, Espirito Santo, Gias, Mato Grosso do Sul, Minas Gerais, Para, Paraiba, Pernambuco, Piavi, Rio Grande Norte and Sergipe including Bahia and Ceara (WHO expert committee report, 1991). Recently the foci of VL has shifted from rural villages to large cities probably as a result of migration of settlers from villages into these cities creating densely populated ghettos living sub-standard housing with improper sanitation and keeping farm animals in their gardens. The two cities of Teresin and Sao Luis together accounted for 40-50% of the total number of VL cases in Brazil during 1993 and 1994, that is approximately 3000 cases per year (Arias et al,1996). In central America, where previously only isolated cases of VL were recorded, the disease is on the increase. Especially in Costa Rica, Honduras and Nicaragua.This is most probably due to an increase in the human population and their movements in and out of these areas (Carreira, 1995). Since the first reported case of VL in Sudan in 1938, the disease has become wide spread and is endemic in south and eastern parts of the White Nile and Upper Nile states (Hashim et al, 1994). Other areas affected include the provinces of Kasala, Jonglei and Kapoeta in the south, El Fasher and El Nahud in the west and also north of Khartoum (WHO expert committee report, 1991). As in most countries males are almost twice as likely to be affected by VL than females, with young children being at the highest risk. In the village of Um-Salala in eastern Sudan, the average age of VL patients was found to be 6.6 years with a male to female ratio of 1.8:1 and an annual incidence rate of 38.4 per 1000 population between 1991 and 1992, and 38.5 per 1000 during the period 1992 and 1993 (Zijlstra et al, 1994). The first case of VL in Ethiopia was documented in 1942 in the southern parts of the country. Since then the disease has spread to become endemic in the Segen, Woito and Gelana river valleys. The highest incidence has been recorded in the Aba Roba area (WHO expert committee report, 1991). During an 8 year study leading upto 1990, 142 cases of VL were reported in the villages close to the Segen river valley. It was found that 58% of the people affected were children below the age of 15 years with the lowest risk groups being males above the age of 39 years and females above 24 years, also surprisingly, children below the age of 5 years. The reason for this reduced risk is not clear, however it is probably due to acquired immunity in the adult population (Ali et al, 1994). However this does not explain the reduced risk in the children younger than 5 years of age. In Somalia sporadic cases of VL first appeared in 1934, mainly in the Middle Shabelle and Lower Juba areas. A recent retrospective study has shown that VL is endemic in these areas. Children below the age of 15 years were at the highest risk and males were over three time more susceptible than females (Shiddo et al, 1995). In Israel VL is rare and the few cases that have been reported are largely confined to the run down Arab villages in western Galilee, proving that the disease is linked to poverty, poor sanitation and sub-standard housing. Between 1960 and 1989, 62 cases of VL were recorded with only 18 cases in the past 13 years and 6 cases of infantile VL between 1992 and 1994. This fall in the incidence rate is most probably due to improved standards of living, diet and the use of insecticides (Ephros et al, 1995). The number of Post kala azar dermal leishmaniasis (PKDL) cases is roughly proportional to that of Kala azar (Ramesh et al, 1995). However the data available shows variable results. In Kenya, three independant studies showed that PKDL occurred in 1%, 6% and 30% of the Kala azar patients repectively (Zijlstra et al, 1995). Another study in Sudan carried out over a period of 2 years between 1991 and 1992 showed that 56% of the Kala azar patients developed PKDL (Zijlstra et al, 1994). The highest prevalence of PKDL is believed to be in the 20-40 years age group with children below the age of 10 years and adults above the age of 40 years at low risk with males and females being equally affected or perhaps females slightly less than males (Ramesh et al, 1995). In Sudan however, it was found that males are almost twice as likely to develop PKDL than females and all children even below the age of 5 years are at high risk. It was shown that 78% of PKDL cases occurred in the 0-1 years age group and 81% in the 2-3 years age group compared to the over-all incidence rate of 56% (Zijlstra et al, 1995).

Foci of old world VL

The following is an alphabetical list of countries where VL is known to exist. This list is by no means complete, it is here only to serve as a rough guide to the global foci of VL (compiled from, WHO expert committee report, 1990; Rab et al, 1995; Zijlstra et al 1995, Ramesh et al, 1995; Al-Masum et al, 1995, Carreira, 1995; Arias et al, 1996).

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