Introduction

Helicobacter pylori (Hp) is the most common chronic bacterial infection in humans worldwide. Its prevalence is higher in developing countries (80 % to 90 %) than in industrialized nations [1, 2]. Poverty, poor drinking-water quality, infected parents, and ethnicity are included among the risk factors associated to its high prevalence [3–6]. Such factors have been also widely involved in the epidemiology of intestinal parasite diseases.

Co-infections by Hp and punctual intestinal parasites have been studied in previous investigations with different purposes and controversial outcomes [7–15]. Some of these studies have suggested that antagonist and/or synergistic interactions between these agents could trigger significant consequences for human health, probably depending on hosts and environmental circumstances [12, 13, 15]. In this respect, it has been proposed that certain intestinal parasites could reduce the probability of infection by Hp. In fact, a minor prevalence of infection by this microorganism has been described in subjects with Ascaris lumbricoides and Entamoeba histolytica [15, 16]. Nevertheless, the nature of such interactions has not been enough clarified up to date. From the epidemiological point of view, it could be assumed that if Hp and intestinal parasites have similar transmission routes or share environmental risk factors for the acquisition and retention of infection, prevalence and coexistence of both types of agents should be very high in populations with poor living conditions, such as those predominant in indigenous communities of Latin America. On the other hand, if indeed intestinal parasites exert some type of protection against Hp, then the prevalence of this infection should be lower in communities exhibiting chronic intestinal parasitic infections. Elucidation of this matter could contribute both to the knowledge regarding the effects that these infectious agents have on the human gastrointestinal (GI) tract and to the formulation of new prevention and control strategies against Hp infection in high risk populations.

Therefore, the purpose of this study was to investigate Hp prevalence and its possible association with a wider variety of intestinal parasitic infections. Its study was realized in a Venezuelan indigenous community whose living conditions appear to favor the prevalence of both types of infectious agents, further contributing to characterize these infections in this minority ethnic group of Latin America.

Methods

Population

This investigation was performed on an “Añu” native community located on the Sinamaica Lagoon, Zulia State, Northwest Venezuela. The Añu, whose name means “water people,” live on rudimentary houses built with mangrove branch and thatch, supported on stilts over the water or on the shore’s humid grounds. Their houses lack potable water and of an adequate excreta and waste disposal. Served water, feces, and waste drain directly into the lagoon, which is also used for consumption and domestic activities. Potable water is delivered in tank trucks to the nearest town and then taken by boat to the houses where it is stored in improvised barrels. Additionally, a wide variety of animals walk around and inside the houses. Rudimentary fishing and handcrafts are their principal economic activities.

Sixty-two Añu family groups were randomly selected, representing approximately 10 % of all families living in the lagoon to the time of the study. The selection was made using a sketch with the distribution of housing, prepared by the Culture Department of the Universidad del Zulia. All participants were informed about the characteristics of this study obtaining their previous written consent. Parental authorization was requested for children participation. The survey was performed in 318 individuals with or without GI symptoms: 167 children (age range 3 months to 15 years old; age average 7.4 ± 4.1 years old) and 151 adults (age range 16 to 84 years old; age average: 39.1 ± 17.1 years old).

Biological samples and data collection

A structured verbal interview was administered to the mothers or grandmothers of the Añu community in order to obtain information regarding the family members including age, sex, socioeconomic status (Graffar scale) [17], the presence or absence of humid soil around the houses, the presence of children under 14 years old and number of children at home, overcrowding, and markers of exposure to fecal-oral transmission route: access to potable water, treatment applied to drinkable water (chlorine vs. non-chlorine), and keeping animals at home or surroundings.

Biological samples were collected in every home. Venous blood (5 to 10 mL) was aseptically collected from each participating individual. Serum aliquots were preserved at −20 °C. A fresh stool sample was obtained from each individual, analyzed the same day (coproparasitological test), and then preserved at −20 °C for subsequent detection of Hp antigens.

Detection of seropositivity and active infection by H. pylori

Detection of the IgG serum antibodies, specific for Hp antigens, was performed using a commercial enzymatic immunoassay (Pyloriset® EIA-G III, Orion Diagnostic, Espoo, Finland) following the manufacturer’s instructions. High sensitivity and specificity have been previously reported for this test in other countries [18, 19], and its high sensitivity (100 %) has been also proven in an ethnically mixed population of the State of Zulia, Venezuela, using a combination of microbiologic culture, rapid urease test, and the polymerase chain reaction in biopsies, as a gold standard [20].

As an indicator of active infection, fecal excretion of Hp specific antigens was determined in 163 seropositive individuals randomly selected, using a commercial enzymatic immunoassay (Premier Platinum HpSA®, Meridian Diagnostics, Inc., Cincinnati, USA) following the manufacturer’s instructions. This trial presented a sensitivity of 100 % and a specificity of 79 % in a sample of ethnically mixed population of Caracas, Venezuela [21].

Coproparasitological diagnosis

Fresh stool samples were analyzed to detect parasites through a direct microscopic examination using saline solution, temporary staining for protozoa (Lugol and buffered methylene blue), and the modified Ritchie concentration technique (formalin/ethyl acetate). In this study, no specific diagnosis method was applied for Enterobius vermicularis. Parasitic forms similar to E. histolytica were reported as “Entamoeba histolytica/E-dispar complex.” All stool preparations were independently examined by two expert parasitologists.

Statistical analysis

The statistical significance of the differences, dependence between variables, and linear tendencies were determined by the χ 2 test (p < 0.05). Risk factor analysis was based on the odds ratio (OR) with 95 % confidence intervals.

Results

H. pylori prevalence

Seropositivity for Hp was detected in 76.4 % of the population sample, being higher in adults than in children (Table 1). The specific fecal antigen excretion of the microorganism was positive in 93.9 % of the seropositive individuals studied, with no significant difference between children and adults (data not shown). Since this test was not practiced on seronegative individuals and taking into consideration that active infection was found in the majority of the seropositive individuals, seropositivity was the parameter used for the subsequent analysis.

Table 1 Prevalence of H. pylori seropositivity and enteric parasitic infection in children and adults
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Intestinal parasites prevalence

The presence of intestinal parasites was evidenced in 89.6 % of the individuals, with predominance of polyparasitism (more than one parasite species in one individual) and protozoan infections, both children and adults. The prevalence of helminth infections resulted considerably lower compared to the protozoan infections even in children (Table 1).

H. pylori and intestinal parasite infections by age group

Upon analyzing seropositivity for Hp and intestinal parasite infections by age group, a high prevalence of both types of infections was evidenced since early childhood. However, parasitic infections in general, and protozoan, outnumbered the Hp seroprevalence, even in adults (Fig. 1). During the first life decade, an ascending tendency in the prevalence of almost all the investigated infections was observed. Hp seropositivity reached its maximum level during adulthood (∼90 %). In contrast, prevalence of Giardia lamblia and helminths tended to progressively diminish with age (Fig. 1).

Fig. 1
figure 1

Prevalence of H. pylori seropositivity and enteric parasitic infections, according to age groups. p-values for linear trends (χ 2 test): H. pylori, helminths, and G. lamblia: p < 0.01; parasitic infection: p < 0.05; poliparasitic infection and protozoan: p > 0.05

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Association between H. pylori and intestinal parasites

Seropositivity for Hp resulted significantly associated to polyparasitism and helminths in children. The presence of these forms of parasitism doubles the risk of Hp infection in this population group (Table 2). An ascending tendency for Hp seropositivity in relation to the number of infecting parasite species was observed in children, with a risk six times greater for seropositivity in the presence of simultaneous co-infection by four or more parasite species (Fig. 2). Additionally, Hp seropositivity was greater in individuals with protozoan (Table 2); however, these parasites behave as a risk factor for Hp in the total population, but not in children or adults separately. It is important to emphasize that, statistically, G. lamblia behaved as a protection factor against Hp infection in the total population sample, being the risk of seropositivity 0.4 times lower in individuals with this protozoan than in individuals free of it (p < 0.01) (Table 2).

Table 2 Enteric parasitic infections as risk factors for H. pylori seropositivity, in children and adults
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Fig. 2
figure 2

Trend H. pylori seropositivity in children and adults depending on the number of parasite species detected. χ 2 14.28 in children (p < 0.01); 3.54 in adults (p > 0.05). Asterisk indicates OR to four or more parasites in children: 6.24; 95 % CI: 2.01–19.41 (p < 0.01)

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Figure 3 shows the analysis of associations between intestinal parasites and Hp seropositivity in age groups less than 20 years. In individuals with polyparasitism, helminths, or protozoan, a higher seropositivity was evident in most of age groups, when they were compared with non-parasited individuals. Nevertheless, it was significant only in the 0–5-year-old group with helminths and in the 16–20-year-old group with protozoan infections. With respect to the negative association between G. lamblia and Hp, it was present in several age groups but only resulted significant in the 6–10-year-old age group. In other adult age groups, no significant associations were obtained (data not shown).

Fig. 3
figure 3

Association between H. pylori seropositivity and parasitic species by age group Capital letters identify the species of parasites: A Ascaris lumbricoides, B Entamoeba coli, C Endolimax nana, D Giardia lamblia. The numbers identify age groups: 1 0–5 years, 2 6–10 years, 3 11–15 years, 4 16–20 years. *p < 0.05; ** p < 0.01

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Risk factors for H. pylori and intestinal parasite

In an attempt to identify possible shared risk factors that could explain the positive associations between Hp and certain intestinal parasite, some environmental markers indicative of exposure to fecal-oral transmission route were researched. It is important to recognize that the living conditions of the population hindered the independent and objective study of these factors. Variables such as overcrowding, non-chlorinated water, presence and number of children at home (more than three) were risk factors only for intestinal parasite infections. Humid soil surrounding the houses constituted a risk factor only for geo-helminths infections. None of the studied variables behaved as a shared risk factor for Hp and intestinal parasites (data not shown). Due to the fact that all participants belonged to the socioeconomic stratum IV or V (poverty or extreme poverty as per the Graffar scale), it was not possible to analyze the role of the socioeconomic stratification as a risk factor within this population.

Discussion

Indigenous communities are among the poorest groups in Latin America. Geographical and socioeconomic segregation turns them into an easy target for acquisition of infectious agents. Therefore, microbiological research in these human groups could be very useful from an epidemiological perspective. For these reasons, an indigenous “Añu” community of Venezuela was chosen for this research. Although intestinal parasite infections has been frequently studied in this type of communities, the epidemiological characteristics of Hp infection and its possible association with the first one has been scarcely investigated.

The high Hp seropositivity detected in the Añu community, both in adults and children, is similar to the previously described in other Latin American ethnic minorities [10, 12, 22, 23]. Nevertheless, prevalence rates different from the ones reported herein have been documented in children from some Amazonian indigenous groups [12, 22, 23]. Such variability could be related to cultural or environmental differences. To support this argument, some investigations have attributed a significant influence to socioeconomic and seasons variations on the prevalence of Hp infection [24, 25]. In agreement to the high seropositivity for Hp, an elevated prevalence of active infection by this microorganism was also detected in Añu individuals; this suggests that microorganism eradication through spontaneous clearance or pharmacological treatment is rare in this population. A high re-infection rate could also explain these results.

Regarding the observed increase in Hp seroprevalence with age, this could obey to the continuous risk of infection during lifetime, as it has been proposed for other communities with deficient life conditions [26, 27]. The high frequency of parasite infections in Añu individuals of all age groups seems to support this argument. Although some authors have attributed similar results to a possible “cohort effect” based on the improvement in the quality of life of the communities through the years [28–30], there is scarce evidence in favor of an economical or environmental evolution in the Añu community. In fact, both children and adults continue to consume and use the lagoon’s water in spite of its increasing fecal contamination [31].

The high intestinal parasite prevalence, the degree of polyparasitism and the predominance of protozoan infections, confirms that the life style of Añu community is favorable for the permanent contact with infection sources and re-infection by GI microorganisms. On the other hand, helminth infections could be the consequence of periodic exposures of Añu to humid soils contaminated with human and animal stool residues, whenever the lagoon’s water level descend during the dry season. It has been previously described that the type of soil, temperature, and environment humidity of the Sinamaica Lagoon favor the preservation of the infecting power of helminth’s eggs [32].

In the present work, Hp and intestinal parasite infections resulted directly and significantly associated, as deduced from the similar prevalence of both types of infections regarding age, especially during the first two life decades. This suggests the presence of shared epidemiological elements for both types of infections, one of which could be the fecal-oral transmission route. Other authors have used this argument to explain some associations between Hp and intestinal protozoan, as G. lamblia and Blastocystis hominis [14, 33]. However, the environment exposure markers to the fecal-oral transmission route investigated herein did not associate to the Hp seropositivity or any parasite species in particular. It is necessary to recognize that the elevated frequency of both groups of infectious diseases (Hp and intestinal parasites), their endemic character, the high frequency of coinfection, and the homogenous life style of this population may have masked any possible relation between environmental factors and such infections.

Some authors have proposed that infections by Hp and G. lamblia could be directly associated, particularly in children [14, 34, 35]. In contrast, there are no reports regarding inverse associations between these agents such as the one evidenced in the Añu community. This interesting finding could suggest the existence of an antagonistic interaction between Hp and some intestinal parasite. One possible explanation for these findings is that Hp, by means of excreting some products containing antimicrobial activity, may limit the colonization by exogenous intestinal pathogens [36]. Indeed, it has been described that children who are Hp-positive have less probabilities of suffering diarrheic diseases than children who are Hp-negative [36, 37]. Inverse associations between Hp and the parasites E. histolytica or A. lumbricoides have been previously attributed to an immunomodulatory effect induced by these parasites through of a Th2-predominant immune response [15, 16]. Previous investigations seem to support this argument. In certain endemic areas, G. lamblia infection seems to induce a persistent elevation of the secreting IgA [35], an antibody with certain protective effect against Hp [38, 39]. Therefore, the possibility that the inverse association between Hp and G. lamblia might be due to a protective mechanism of immune type triggered by the parasite should be considered. However, demonstration of such hypothesis is beyond the scope of this investigation.

In conclusion, the Añu indigenous population exhibited a high rate of seropositivity and active infection by Hp as well as an elevated prevalence for intestinal parasites. There are significant associations between certain enteroparasite and Hp seropositivity which are more evident in children. Parasite species involved in such associations and the risk factors for both types of infection are different to the ones previously reported; this might be due to a particular combination of factors inherent to the surveyed community. The results of this investigation contribute to support the important role of the fecal-oral route for the combined transmission of Hp and some intestinal parasites in the Añu population, while the inverse association between H. pylori and G. lamblia points out to the existence of a protective interaction between these microorganisms. Additional investigation is required to explain the nature of such interaction.