Echinococcosis, toxocarosis and toxoplasmosis screening in a rural community in eastern Kazakhstan.

OBJECTIVE: To determine the extent of carnivore-transmitted parasitic zoonoses in a community in eastern Kazakhstan, a region where cystic echinococcosis (CE) re-emerged in recent years. METHODS: Cross sectional ultrasound study of 3126 human subjects to determine the extent of human cystic and alveolar echinococcosis (AE). Blood samples were taken from each subject and analysed for antibodies against Echinococcus, Toxocara and Toxoplasma spp. Each subject was questioned about possible risk factors that might be associated with zoonotic transmission. Analysis employed a mixed modelling approach based on the results of the ultrasound study, the serological results and the results of the questionnaire. Bayesian techniques were employed to estimate diagnostic performance. A helminthological study of the local dog population was also undertaken. RESULTS: A total of 23 subjects tested positive for CE on ultrasound and a further three individuals had strong serological evidence of infection. Another 24 reported treatment for CE. Ultrasound lesions or treatment for CE were associated with poverty. No ultrasound evidence of AE was found, but one individual had strong serological evidence of exposure to Echinococcus multilocularis. Toxoplasma seropositivity (16%; 504 individuals) increased with age. Household level Toxoplasma-seropositivity was associated with unsafe drinking water. Toxocara seropositivity (11%; 349 individuals) was more frequent in children and in individuals who disposed of dog faeces on the vegetable garden. A purgation study of dogs indicated that 13% of dogs in the community were infected with Echinococcus granulosus, 5% with E. multilocularis and 2% with Toxocara canis respectively. CONCLUSIONS: There is significant transmission of E. granulosus to humans in this community. Transmission may be associated with poverty. There is little evidence of E. multilocularis transmission to humans, despite the presence in the parasite in the domestic dog population. Toxoplasma is actively transmitted and there is evidence for transmission by the water supply. Children are at highest risk of exposure to Toxocara.

Distribution and ecology of Echinococcus multilocularis in Central Asia.

Much of Central Asia is characterized by an arid landscape. Foci of Echinococcus multilocularis have a very patchy distribution. This is due to a significant deficiency of moisture in the superficial layers of the ground and is related to the types of animal colonies. In the plain, the abundance of endemic foci increases in a direction from the sandy deserts to steppe. In mountains the highest levels of infection of animals are observed in the eastern part of region. In arid regions, E. multilocularis is typically located in humid mesophilous biotopes. Here there is sufficient moisture in the spring to promote survival of eggs and there is a close interrelation between the definitive and intermediate hosts.

Present situation of cystic echinococcosis in Central Asia.

Cystic echinococcosis (CE) caused by Echinococcus granulosus has always been an endemic disease in central Asia. During the period of Soviet Administration up to 1991, human surgical incidence rates tended to be relatively low with perhaps at most 1-5 cases per 100,000 per year. Following the collapse of the Soviet Union and the emergence of the New Independent States there has been profound economic and social changes. Associated with this has been a serious epidemic of CE throughout the region. In many areas figures suggest the surgical incidence is now greater than 10 cases per 100,000. Furthermore, official government figures are believed to substantially under report the extent of the problem. For example, official figures in Uzbekistan reported 819 cases of CE surgically treated in 2001. However, a detailed analysis of hospital records suggests that the true figure was 4089, more than 4 fold higher. The latter figure represents an annual surgical incidence rate of nearly 25 cases/100,000 per year. Similarly high endemic areas are seen in southern Kazakhstan, Kyrgystan and Tadjikistan with incidence rates of up to 13 cases/100,000, 20 cases/100,000 and 27 cases/100,000 respectively. A disproportionate number of cases are in children and the unemployed. The rates of infection have also increased in major livestock species such as sheep with a doubling of reported prevalence in some areas. In the dog population, independent studies in Uzbekistan and Kazakhstan have demonstrated that the rural dog population, closely associated with the sheep industry, is highly infected, with prevalences approaching 25%. Village and urban dogs have a considerably lower prevalence.

Helminths of saiga antelope in Kazakhstan: implications for conservation and livestock production.

Saiga antelope (Saiga tatarica) graze extensively on livestock pasture, potentially enabling transmission of a wide range of parasitic helminths between saigas and domestic ruminants. Thirty-six of the 38 species of helminth that have been found in saigas in Kazakhstan in the past have been found also in domestic livestock. We examined 133 saigas culled for meat in autumn 1997, and found three species of cestode and 12 nematodes (nine in the abomasum), but no trematodes or lungworms. The most abundant species were Marshallagia marshalli, Marshallagia mongolica, and Nematodirus gazellae in the abomasum, Nematodirus gazellae in the small intestine, and Skrjabinema ovis in the large intestine. There was no clear relationship between intensities of abomasal nematodes and body condition. Age-intensity patterns differed between species: N. gazellae intensities were highest in saigas around 2-3 yr old, and declined in older animals, whereas the intensity of Marshallagia spp. rose asymptotically with age. Fecal egg density was directly proportional to adult worm intensity across ages for Marshallagia spp., but only in young animals for N. gazellae. There was no evidence that helminths, at the intensities observed, adversely affect saiga populations. The host range of many of the parasites found is broad, and transmission between saigas and livestock in both directions might become important to agriculture and conservation as livestock numbers recover. Simplified sampling techniques used in this study, and statistical analysis based on bootstrapping, could prove useful in other parasitologic surveys of wildlife in remote areas.