Schistosomiasis japonica in the Philippines: the long-term impact of population-based chemotherapy on infection, transmission, and morbidity.

The long-term impact of annual case-finding and chemotherapy with praziquantel on schistosomiasis japonica was examined in an 8-year longitudinal study in the Philippines. The prevalence, incidence, and intensity of infection and schistosome-induced hepatomegaly significantly decreased within 3-4 years of treatment and then stabilized despite continual population-based chemotherapy. Hepatomegaly rapidly developed in acutely infected persons, with 82% of subjects developing hepatic enlargement within 2 years of reinfection. These data suggest that abrupt discontinuation of current control measures in the Philippines may result in a rapid rebound in morbidity. Age-dependent acquired resistance to reinfection also developed in subjects chronically exposed to schistosomiasis japonica, suggesting that a vaccine may represent an alternative approach for control of this parasitic infection.

Seroepidemiology of hepatitis B virus in the Philippines.

Hepatitis B virus markers were studied in 2,842 Philippine rural subjects from four villages in 1979-1982. The prevalence of hepatitis B surface antigen (HBsAg) and all markers for hepatitis B virus averaged 12% and 58%, respectively, in these rural populations. It is estimated that five million Filipinos are HBsAg positive. The rural age-specific HBsAg prevalence shows an "early peak" (in persons 3-4-years-old) in two communities and a "late peak" (in persons 30-40-years-old) in the other two communities. Family studies suggest that the prevalence of HBsAg and hepatitis B e antigen (HBeAg) among parents of the young children in an "early peak" and a "late peak" village cannot fully account for the difference in the patterns of prevalence of all markers, or the HBsAg marker. Horizontal intrafamilial and extrafamilial transmission may also be significant. Further research is needed on risk factors for hepatitis B virus infection.

HBV exposure and HBsAg positivity rates in schistosomiasis japonica: study in a Philippine community endemic for both infections.

HBV exposure and HBsAg positivity rate were examined in 561 residents of an area endemic for S. japonicum and 22 additional cases with severe HSS japonica were also included. The differences in HBV exposure and HBsAg positivity rates among the groups without the parasitism, with schistosomiasis japonica and with HSS (53 cases) were not statistically significant. Comparison of the same parameters between those with and without S. japonicum infection according to sex and age groupings did not also show significant differences. Increasing intensity of S. japonicum infection was not associated with either increasing or decreasing HBV exposure and HBsAg positivity. It is postulated that HBV infection does not contribute to the production of HSS japonica mainly because HBV infection occurs at a much earlier age than S. japonicum infection.

Relationship of prevalence and intensity of infection to morbidity in schistosomiasis japonica: a study of three communities in Leyte, Philippines.

To determine whether prevalence and intensity of infection are factors in morbidity in schistosomiasis japonica, a cross-sectional study was undertaken in three villages in Leyte, Philippines, namely, Santol (A), Santa Rosa (B), and Macanip (C). Kato thick-smear fecal examination and egg counts were made on 289 of 341 residents in Village A (85%), 824 of 1,008 in Village B (82%), and 1,113 of 1,241 in Village C (90%). Prevalences of 26%, 39%, and 44%, respectively, were found in the three villages, the majority of their populations (56-74%) remaining uninfected. Most of the infected persons (17-30% of the total population) had light infections (10-100 eggs/g feces). Moderately infected persons (101-400 eggs/g) comprised a smaller segment (7-14%), while a very small proportion (2-7%) had heavy infections (greater than or equal to 401 eggs/g). Age prevalence and egg excretion peaked earlier in the areas with higher prevalence (B and C) than in the area with the lowest prevalence (A). There was no relationship between area prevalence and mean egg count. Symptoms of inability to work, weakness, abdominal pain, and diarrhea correlated with the presence of infection in the area with the highest prevalence (C), but not in the area with the lowest prevalence (A). Except for diarrhea, there was no relationship between symptoms and intensity of infection. Very few persons presented with hepatomegaly and/or splenomegaly (1-5%). The frequency of liver enlargement on the midsternal (measuring 3-6 cm and 6 cm or more) and midclavicular line (2-4 cm), as well as spleen enlargement (Hackett 2 or greater), correlated with the presence but not with the intensity of infection. Hepatomegaly was sex- and age-related, being most common among males and among adolescents aged 10-14 years.