Severe cases of hepatitis caused by hepatitis B virus (HBV) or hepatitis D virus (HDV) are often seen in the Brazilian Amazon, but there is a paucity of epidemiologic studies on viral hepatitis in this area. Thus, a cross-sectional study to investigate the prevalence of markers for HBV and HDV was performed. Serum samples were collected after participants completed an epidemiologic questionnaire. Markers for HBV and HDV were analyzed with an enzyme-linked immunosorbent assay. The HBV genotype was determined by sequencing of the gene for hepatitis B surface antigen (HBsAg). Of 2,656 samples, 89 (3.3%) were positive for HBsAg and 1,628 (61.5%) were positive for IgG antibody to hepatitis B core antigen. Markers for HDV were found in 47 cases (1.7%). Antibodies to HDV were associated with Amerindian ethnic origin, a lower educational level, a history of acute viral hepatitis, a history of malaria, male sex, a history of tattooing, and older age. The most frequent HBV genotypes were A and F. This study showed a high prevalence of HBV and HDV in the western Brazilian Amazon, as well as the predominance of HBV genotypes A and F.

In Brazil, hepatitis delta virus (HDV) is only reported in Western Amazonia, where severe cases of acute and chronic HDV hepatitis have been described. The study area was chosen in the States of Acre and Rondonia where most cases of hepatitis B virus (HBV)/HDV are reported. From December 2003 to October 2004, 40 HBsAg carriers with anti-HDV IgM were selected. An epidemiologic questionnaire, including demographic and clinical/epidemiologic variables was filled out. HDV amplification and genotyping were performed. Genotype I was detected in 22 patients (55.0%), whereas genotype III was identified in 18 (45.0%). Patients who were infected with genotype I were older (45.1 +/- 17.8 years) than patients infected with genotype III (32.8 +/- 10.9 years; P = 0.01). No symptoms were reported by 21 (52.5%) patients. Otherwise, 19 (47.5%) had symptoms (fatigue, abdominal pain, weight loss, and decompensated liver disease) that motivated them to seek medical care. Genotype III carriers were more symptomatic, but no statistical significance was achieved. Our preliminary results show that HDV genotypes I and III are present in Brazilian Amazonia and that HDV genotype III is not limited to the Amerindian population.

During a yellow fever vaccination campaign among residents of Rio Branco (Acre State), the frequency of HI antibodies to the most prevalent arboviruses in the Amazon region and to yellow fever virus was determined before and three months after immunization with YF 17D vaccine. From 390 inhabitants included in the first phase of serologic survey (August 1999), only 190 provided a second serum sample, after the use of 17D vaccine (January 2000). Among first phase samples, the frequency of HI antibodies was: 17D (27.2%); Ilheus (5.9%); Mayaro (5.4%); Caraparu (4.9%); Dengue-2 (4.1%); Oropouche (2.3%); and Dengue-1 (0.3%). In the second study phase, the serologic conversion to YF reached 89.7% among previously negative persons. Serologic conversions were also observed to Ilheus (6.2%); Dengue-3 (3.2%); Mayaro (1.1%); and Oropouche (1.1%) viruses. In conclusion, considering the high YF antibody rate after vaccination, the risk of urban yellow fever seems insignificant, although the lower prevalence of HI antibodies to dengue viruses, is of concern and inhabitants are under high risk of dengue outbreaks, especially to DEN-3 recently introduced in Brazil, as was observed in 2000 and 2001 with DEN-1 and DEN-2.

In 1999, on the occasion of the application of the first vaccine dose during the state vaccination campaign against hepatitis B virus (HBV), 390 individuals from the town of Rio Branco, Acre, aged two or more years were selected for the determination of the seroprevalence of HBV and HCV. HBV markers (HBsAg, anti-HBs, and anti-HBc IgG) were determined on this occasion and anti-HBs antibodies were also assessed 30 days after the third vaccine dose. At the time of vaccination, 39% of the individuals were still susceptible to HBV, while 61% presented serologic evidence of previous HBV contact or previous vaccination. The individuals with previous HBV contact were significantly older (p<0.001) than those without HBV markers. Of the 192 individuals who returned for reexamination, 30 days after the third dose, 158 (82.3%) had received three vaccine doses, and only 60 (31.2%) belonged to the group without HBV markers. In these individuals, the seroconversion rate after the third dose was 92% (55/60). In conclusion, we found considerable HBV in this population, indicating the need for pursuing the immunization programs. We also found high rates of vaccination coverage in the Western Brazilian Amazon region.

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