The target population is young (averaging 26 years) and has been living in Rondonia for 21 years, 14.8 of those years in the Rio Preto area. Most of the population is composed of native individuals (79%), fishermen, or people engaged in subsistence agriculture (41%) with a malaria prevalence of 4%. The technique used here is highly specific for C. hepatica and the findings confirmed the presence of antibodies against this nematode in the western Brazilian Amazon, thus indicating the occurrence of infection among the sampled population. Nevertheless, in spite of its dispersion, this parasitic disease seldom seems to induce illness, since none of the patients analyzed showed symptoms of hepatic capillariasis. However, when subjects become ill [13, 21–25], disease evolution is generally serious .
The prevalence found in the target population of this study (34.1%), independently of its reactivity (weak, median or strong), is roughly similar to the 44.2% value reported by Galvão  when he studied 500 low-income children in Salvador, Bahia, northeastern Brazil. Galvão  associated the high prevalence observed with some factors such as the low socio-economic level of the population and the possibility of rat carcasses exposing embryonated eggs in the environment, thus causing contamination . However, our results show that after diluting the sera, the prevalence value dropped to 0.81%, thus suggesting that the occurrence of false-positive cases is significant when the dilution of 1/150 is used. The same phenomenon was observed by Galvão , who reported a drop in prevalence to 1.8% after diluting the positive sera to 1/500.
In another study with samples from 60 workers of the Vienna Zoo, Juncker-Voss  found a serum prevalence of 3.3% in sera diluted 1/40 using the indirect immunofluorescence technique. All serum positive workers were asymptomatic, with no hepatic enzyme alterations, and remained so until the conclusion of the study. After two months, serology was repeated and the test remained positive in only one of the patients. In order to test the accuracy of the diagnostic tool, patients' sera were further tested by ELISA and by the indirect immunofluorescence technique with antigens against Echinococus granulosus, E. multioculares, Toxocara canis, Schistosoma mansoni, Fasciola hepatica, Trichuris trichiura and Trichinella spiralis, showing no positive reactions and suggesting a high specificity of this test for C. hepatica. The authors suggest that the infections by C. hepatica originated from carcasses of Mus musculus, which were abundant in the zoo.
An experimental study with Wistar rats  confirmed the excellent sensitivity and specificity of the indirect immunofluorescense technique and estimated that positivity starts 15 days after infection and lasts for three months. In false-positive cases (ingestion of non- embryonated eggs) reactions are initially positive; however, dilutions equal or greater than 1/400 show a negative reaction. Moreover, infections with over 3 months of duration show negative reactions, thus suggesting a fall in antibody level as the eggs are destroyed in the hepatic tissue.
Considering these previous studies and in view of the high serum prevalence (34.1%) found at the initial dilution of 1/150 in the present study, we may conclude that this riverine population is in great contact with non-embryonated and embryonated eggs of C. hepatica, When positive sera were further diluted to equal or greater than 1/500, the prevalence falls to 0.81% (two patients). All patients with medium or high serology reactions, when first examined, did not present clinical symptoms nor liver alterations at the biochemical or ultrasonographic levels, thus characterizing a parasite of low pathogenicity, as many authors have proposed [13, 21–25]. On the other hand, it is probable that there is a low environmental contamination with embryonated eggs, due to the high dispersion of people in this area, which could lead to infections with a low quantity of eggs and a consequent benign evolution of the disease. It must be considered that many authors have registered the contrast between the abundance of C. hepatica eggs in the environment and the rare occurrence of clinical cases of the disease [28–31]. These findings corroborate the low prevalence of carriers for the nematode C. hepatica.
Nevertheless, we must consider that since the present study focused on prevalence and since the antibodies do not remain in the blood for over 3 months , timely antibody detection is required. Thus, it is possible that the exposure to C. hepatica could have been underestimated in the sampled population.
The similarity of the serum prevalence distribution according to sex and among the three age groups indicates that the risk of exposure is equivalent among the population. This result contrasts with Galvão , who reported that the highest infection risk was among children, who were supposedly more exposed to eggs and rats' carcasses.
Another interesting finding is the greater serum prevalence in individuals original from the Amazon region, when compared to those original from outside the Amazon. This higher prevalence in Amazonian individuals may suggest that cultural habits (eating wild animal viscera) non-existent or less practiced by non-Amazonians is a factor to be considered in the infectivity of C. hepatica. However, the overall high serum prevalence found in the sampled population may be explained by the relatively few people from outside the Amazon that live in the region.
Contrary to the hypothesis formulated by Galvão , who proposed that people are contaminated by embryonated eggs from carcasses of urban rodents (which do not exist in the Amazon rain forest), we hypothesize that the riverine population under study can be exposed to the parasite's eggs by two non-exclusive mechanisms:
a-) ingestion of non-embryonated eggs from giblets of paca (Agouti paca), peccaries (Tayassu spp.), agouti (Dasyprocta aguti), monkeys and other wild animals . The consumption of giblet "farofa" (dish made of manioc flour browned in oil, mixed with giblets of these animals) is very common among these populations. These individuals may ingest livers contaminated with non-embryonated eggs and then act as carriers, disseminating C. hepatica eggs in the stool. This hypothesis is reinforced by the fact that 91.7% of the interviewed patients affirmed that they had eaten paca, agouti or peccary meat within the fifteen days prior to the interview.
b-) ingestion of environmental embryonated eggs from water or food contaminated with feces of individuals that had consumed contaminated viscera (false-positive) or with eggs from the carcasses of animals. This mechanism would be facilitated by the fact that there are no adequate methods of disposal of human excrements in the area.
These transmission routes may be investigated in the future by examining the subject's feces and investigating whether there is contamination of the soil with C. hepatica eggs.
Due to its particularities, our study area contrasts to other areas previously studied. Galvão  and Junker-Voss  suggested that the rodent Mus musculus seemed to play an important role in the transmission in their study areas. In the riverine population studied here, M. musculus is absent and there is no human agglomeration. Therefore, low transmission, low parasitary load and, consequently, low pathogenicity are observed.