The epidemiology and immunodiagnosis of hydatid disease in Kenya
Gathura, P B
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Hydatidosis is a cosmopolitan cyclozoonosis which occurs with varying intensity in different parts of the world. The disease is caused by the larval stages of Echinococcus granulosus (Batsch, 1786). This zoonosis is endemic in the livestock and human population in certain parts of Kenya. However, there is no survey data available on the national incidence of human hydatid disease in this country. The lack of this kind of data may be partly due to the unavailability of suitable immunodiagnostic tests and/or techniques. Despite that, several investigators have reported that the highest incidence of human hydatidosis in the world occurs in the Turkana District of north¬western Kenya. This study, therefore, aimed at establishing the prevalence of hydatidosis in livestock and the incidence of human hydatidosis in Kenya. The recurrence of hydatid disease in surgically operated patients was also estimated. In addition, the study aimed at assessing the prevalence - of human hydatid disease in Turkana District using an ultrasound scan survey. Man/ dog ratio studies were carried out in the same district. The study aimed at estimating the losses resulting from the condemnation of cattle and smallstock livers due to the presence of hydatid cysts. In addition the study attempted to find suitable immunodiagnostic tests based on the detection of antibodies to the antigen-346 of hydatid cyst fluid in both man and livestock. Enzyme immunoassays and the double diffusion test were used to detect antibodies to this particular antigen. The dot-immunobinding assay XXI (Dot-ELISA) was also evaluated for the diagnosis of hydatid disease in livestock and man. An enzyme immunoassay designed to detect the presence of antibodies to antigens A and B of hydatid cyst fluid was evaluated for the diagnosis of human hydatidosis. The presence of antigen-346 in other parasites was examined for the purposes of establishing alternative sources of antigen for the diagnosis of hydatid disease. The isolation, partial characterization and the assessment of the immunodiagnostic value of a heat stable C. tenuicollis fluid antigen was attempted. An attempt was made to determine the presence of circulating specific immune-complexes to hydatid antigens and to assess their diagnostic value. Meat inspection records maintained by the Ministry of Livestock Development of the Kenya Government were used to estimate the condemnation rates of cattle and smallstock livers and lungs due _ to hydatidosis for an 11 year period (1977-1987). Pooled average annual condemnation rates of 4.82% and 4.12% were obtained for cattle lungs and livers respectively. Condemnation rates of 2.97% for the lungs and 2.58% for the livers .were obtained for smallstock. In both cattle and smallstock, there was no significant change in the condemnation rates of the livers and lungs due to hydatidosis over the study period (p>0.05). The highest condemnation rates for both species were obtained in Rift Valley Province while the lowest were observed in Nyanza and Coast provinces. Pooled average annual condemnation rates of 0.48% and 0.45% were obtained for pig lungs and livers respectively. A significant increase in the condemnation rate of pig lungs and livers was obtained for the 11 year period (p<0.05) .. XXll It was estimated during this study that an average of Ksh. 778,206 is lost annually due to the condemnation of bovine livers infected with hydatid 'cysts. The annual average loss from the condemnation of srnallstock livers infected with hydatid cysts amounted to Ksh 52,945. The average annual actual loss (loss after discounting for inflation) over the 11 year period due to the condemnation of cattle livers was Ksh. 699,314 while that resulting from the condemnation of smallstock livers was Ksh. 47,552. Monetary losses resulting from condemnation of livers of both cattle and smallstock increased from Ksh 132,994 in 1977 to Ksh.l,383,335 in 1987. This represents an increase of 940%. Slaughterhouse surveys were carried out to compare infection rates from animals slaughtered in the abattoirs around Nairobi and those in Turkana District. Infection rates of 15.8% in cattle, 3.12% in goats and 7.65% in sheep were obtained in the Nairobi area abattoirs. Rates of 26.9% in cattle, 4.66% in goats, 5% in sheep and 100% in camels were obtained for Turkana District. Hospital records from the whole country were examined to determine the trends of the incidence of human hydatidosis in Kenya for a 10 year period (1979-1988). A pooled annual average incidence rate of 0.46 cases per 100,000 persons was obtained for the whole country. For Turkana District a pooled annual average incidence rate of 60.53 cases per 100,000 persons was observed. Average incidence rates of 2.40, 1.82 and 1.53 cases per 100,000 persons were obtained for Kajiado, Narok and Samburu districts. There were no statistically significant changes of the incidence of human hydatidosis with time (p>0.05). No cases were recorded from Busia, Wajir, Mandera, Garissa, Isiolo, XXlll Mombasa, Lamu and Tana-River districts. The remaining districts had average annual incidences below 1 case per 100,000 persons. The main anatomical sites, the male:female (M:F) ratios, the age¬specific incidence rates and the recurrence rates were calculated for patients from the various ethnic groups in this country for the 10 year period (1979-1988). The main anatomical site for hydatid cysts in Kenyan patients was the liver with 37.6% of the Maasai, 43.5% of the Turkana, 46.3% of the Kikuyu and 50% of Luhya patients having liver cysts. An M:F ratio of 1:1.99 was obtained for Turkana hydatid patients while that of 1:1.69 was observed for the Maasai. Male: female ratios of 1:1.43, 1:0.82 and 1 :1.50 were obtained for the Kikuyu, Luhya and Samburu respectively. The highest age-specific incidence rate was found in males and females between the ages of 20 to 44 years. Recurrence rates of hydatid cysts in patients from various ethnic groups were also calculated. Among the Turkana a recurrence rate of 8.23% was obtained while among the Maasai the rate was 7.1 %. The recurrence rates among the Kikuyu, Luo and Karnba patients were 7.14%, 30.7% and 20% respectively. The man/ dog ratio studies yielded an average of 0.79 dogs per family and 0.14 dogs per person in the Lokichoggioarea of Turkana District. For Lokichar area in the south averages of 0.16 dogs per family and 0.03 dogs per person were estimated. Ultrasound scan studies of the Turkana gave a prevalence rate of 5.12% in the human population studied. Multiple regression analysis showed that the size of the cyst increased with the age of the patient. Antigen 346 of hydatid cyst fluid was detected in 7 other parasites apart from hydatid cyst fluid. These were Taenia hydatigena, XXIV Cysticercus tenuicollis, C. tenuicollis scolex, Monieza expansa, Taenia saginata cysticerci, Taenia solium cysticerci and unidentified Taenia species from a hyena. The antigen was also found to be present in the fluid and scolices of C. tenuicollis from sheep, goat and pig. Antigen 346 was shown to be present in 70% of human liver hydatid cyst fluid and 100% of human hydatid cyst protoscoleces examined. A heat stable C. ten uicollis fluid antigen was identified and partially characterized by Sephadex G-200 Chromatography. A molecular weight of 410,00 daltons was obtained. The antigen was also tested for its suitability in the immunodiagnosis of human hydatidosis. When used in an enzyme immunoassay (ELISA) the antigen gave a sensitivity of 67.9% and a specificity of 98%. Enzyme immunoassays were carried-out to detect the presence of antibodies to antigen 346 in livestock and human sera. In cattle the test gave a sensitivity of 59.1 %, a specificity of 66.6% and a positive predictive value of 69.6%. For sheep sera the test gave a sensitivity of 61.8%, a specificity of 69.2% and a positive predictive value of 31.5%. The assay for goat sera gave a sensitivity of 64%, a specificity of 63.2% and a positive predictive value of 47.8%. When applied to human serum samples the same enzyme immunoassy test gave a sensitivity of 66.6% with surgically confirmed cases and 70.0% with ultrasound positive cases while double diffusion yielded a sensitivity of 66.6% with surgically confirmed cases. The ELISA test designed to detect the presence of antibodies to antigen A and B gave a sensitivity of 78.0% and a specificity of 81.4%. Dot-ELISA evaluated for diagnosis of hydatid disease in cattle gave a sensitivity of 61.4%, a specificity of 59.0% and a positive xxv predictive value of 66.4%, while for human serum samples, a sensitivity of 76.6% and a specificity of 90% were obtained. It was concluded that hydatid disease is a major problem in Kenya as evidenced by the results of abattoir surveys, the meat inspection records, ultrascan survey and the examination of the hospital records. The problem is still persistent despite improvement in meat inspection services. It was also found that tests designed to detect the presence of antibodies to antigen 346 were useful for the diagnosis of hydatid disease in humans and to some extent in livestock. It was further concluded that heat stable antigen(s) isolated from C. tenuicollis fluid could be used for the diagnosis of hydatid disease in livestock.