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Humans are universally colonized with Helicobacter pylori. Prevalence is universally high in all human groups, until recently; H. pylori is now disappearing from modern societies.1 H. pylori have a geographic genetic structure, the Amerindian strains having Asian characteristics2 consistent with the East Asian ancestry of Amerindians. Today’s Amerindians descend from Asians that arrived in America > 20,000 years ago.3 Divergence between the Central and South Amerindian populations fall between 13,000 and 19,000 years.4 In contrast to Andean Amerindians, some groups east of the Andes have remained in relatively high isolation and have diverged from the former, showing lower levels of intra-population genetic variability.4 In Venezuela, Amerindian groups form small-sized populations, some remaining highly isolated over the years. Warao (Chibchan-Paezan linguistic affiliation) are found in the Orinoco Delta, and Piaroa/Guahibo (equatorial) are in the Amazonas (south). Evidence for this isolation is supported by human microbes. First is viral evidence by Asian type hepatitis GBV-C virus (HGV) circulating among Amerindians groups.5 The lack of common viruses widely found in some Amerindian populations also reflects this isolation. Bari and Yukpa Amerindians from Sierra Perijá, for example, are not infected with hepatitis C virus (HCV).6
Although H. pylori have been found in the stomach of all human populations examined, isolated human groups have barely been studied. We hypothesized that Amerindian groups relatively isolated in Amazonas and in Orinoco Delta of Venezuela would have high prevalence of H. pylori colonization, consistent with their poor hygienic and rural conditions.
Sera were from 18 males and 18 female Amerindians, 10–55 years of age, 19 from the Amazonas Guahibo/Piaroa (average age, 30 ± 13 years) and 17 from Delta Amacuro Warao Amerindians (average age, 23 + 12 years; Figure 1
). The 36 serum samples included in this study were part of an effort pursued in 1991 to study hepatitis viruses.7 Samples were kept frozen at ultralow temperatures, under a code that precludes patient’s identification, and therefore, there was no treatment of any kind offered to the patients as part of this study. The protocol was approved by the IVIC Ethical Committee.
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1.0 in 1:800 sera dilutions was considered positive. To assess serologic response to CagA, a 66-kDa CagA fragment that had been cloned in Escherichia coli as pORV220,9 was used as antigen. For this assay, sera diluted 1:100 were considered positive if the optical density was 0.35.
2 analysis allowed comparisons of proportions of values between groups. In each case, P < 0.05 was defined as significant.
This study examined serum IgG responses of two isolated Amerindian peoples to H. pylori WC and CagA antigens. Only 3 of the 36 subjects were negative to both antigens, and these subjects were young (age, 12, 14, and 19 years). There was a significant association of H. pylori with age (P = 10–14).
Serologic response to either or both antigens seemed to be a better indicator of H. pylori positivity than either antigen alone (Figure 1
). There was a low response to H. pylori WC antigens in relation to what was expected according to recognition of any of the H. pylori antigens (95% in Guahibo-Piaroa and 88% in Warao; Figure 1). A proportion of Guahibo (4/19) and Warao subjects (2/17) were seropositive to CagA but not to WC (Table 1).
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Our Amerindian groups seem to have a high prevalence of H. pylori, unlike in a few isolated human coastal groups in Asia, who have unusually low H. pylori prevalence.12–14 Serology allowed detection of H. pylori in 95% of the Piaroa population. This is consistent with previous results obtained in many other parts of the third world. Because, in Piaroa, sera recognition of CagA antigens was better than that of WC antigens, the CagA antigen test improved the chances of detecting H. pylori. However, the Warao people, in which a similarly high prevalence of H. pylori was expected, showed low seropositivity to both CagA and WC antigens, with 36% of sera recognizing only one of the two H. pylori antigens. The results could respond to three possible scenarios: 1) an impaired Th1 immune response caused by multiple parasitic infections; 2 low H. pylori prevalence; and 3) poor recognition of H. pylori antigens circulating in the United States. Amerindian populations often have a high prevalence of viruses (eg, hepatitis B and G viruses),5 associated with an impaired Th1 response,15 with low numbers of T and B lymphocytes in the peripheral blood. However, a poor Th1 response is not consistent with a high response to the CagA antigen found in the Guahibo/Piaroa population. Because H. pylori is universally present in all human groups—only recently disappearing in industrialized countries—and because the antigenic response against H. pylori has been broadly shown to occur in many human groups, we favor the interpretation of distinct H. pylori strains circulating among Amerindians.
Poor antigenic recognition would mean that strains of H. pylori circulating in the subjects are different to the strains from which the antigens were prepared. Antigens used in our serology were prepared from a mix of five US strains. Serologic responses to H. pylori in Thailand, China, and India have led to suggest that antigen differences have a geographic component.9,16 In isolated human populations, an accurate serology is better achieved by using local antigens.9,16 In a previous work with US strain antigens, serology failed to detect as much as 20% of the H. pylori–positive persons in Ladakh.9
Helicobacter pylori adapts to its hosts, selecting treats that increase fitness and losing those that do not confer competitive advantages. A good example of host adaptation in H. pylori is given by the function of the H. pylori BabA adhesin, which recognizes ABO blood group antigens in the stomach of the human host. Most human societies have people with A, B, and O blood groups, and H. pylori strains from these humans recognize all three blood group antigens. Amerindians, however, have the O blood group, and their strains preferably bind O group antigens.17 Therefore, H. pylori circulating among different human groups are different.
We hypothesize that genetic drift/natural selection within the Amerindian host may have been a source of genetic and antigen divergence. It has recently been reported that some Amerindians have deletions in the cag pathogenicity island,18 which could certainly affect antigenic recognition if antigens are prepared from other H. pylori populations. This preliminary study stresses the importance of pursuing other studies to confirm the hypothesis of antigenic variability among isolated populations, because thus far, commercial serologic tests for H. pylori based on local antigens may fail and lead to false-negative results. An important study should be testing commercial and local serologic tests in Amerindians with a positive H. pylori breath test. In addition, studies performed today in the same locations, 15 years after the sera for this study was collected, will also show if the trend of H. pylori to disappear is confirmed also for these communities.
Received February 18, 2007. Accepted for publication September 7, 2007.
Financial support: This study was supported by the Puerto Rico Alliance for the Advancement of Biomedical Research Excellence (PRAABRE) made possible by Grant P20 RR-016470 from the National Center for Research Resources of the National Institutes of Health.
* Address correspondence to María G. Domínguez-Bello, Department of Biology, University of Puerto Rico, Av Ponce Leon, NCN 343, San Juan, Puerto Rico 00931. E-mail: mgdbello{at}uprr.pr 
Authors’ addresses: Monica Contreras, Flor H. Pujol, and Fabian A. Michelangeli, Venezuelan Institute of Scientific Research, IVIC, Caracas, Venezuela. Guillermo I. Pérez-Pérez, Departments of Medicine and Microbiology, New York University School of Medicine, New York, NY. Elisabetta Marini, Department of Experimental Biology, University of Cagliari, Cagliari, Italy. Liliana Ponce, 10012 NW 41 Street, Doral-Miami, FL 33178. María G. Domínguez-Bello, Department of Biology, University of Puerto Rico, San Juan, Puerto Rico, E-mail: mgdbello{at}uprr.pr.
Reprint requests: María G. Domínguez-Bello, Department of Biology, University of Puerto Rico, Av Ponce Leon, NCN 343, San Juan, Puerto Rico 00931. E-mail: mgdbello{at}uprr.pr.
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