Intestinal parasitic infections are still a serious public health problem in the world, particularly in developing countries [1–4]. These infections are the result of inter-related social, economic, cultural, historical, and political factors [5] Control strategies involving improved drinking water supplies, excreta disposal, sewage management, sanitation, and education have been related with reduced prevalence of intestinal parasitism [6]. Recently, concurrent programmes of nutrition, immunization, family planning, and de-worming have been shown to effectively promote health by influencing the knowledge, perceptions, and behaviour of mothers toward intestinal parasitic infections in countries like Thailand, Guatemala, Uganda, and Egypt [7–10]. These programmes are effective in areas where mothers are trained to give guidance to children and to organise volunteer groups to solve common health problems. In Mexico, a social program targeting mothers has been implemented to ensure the well-being of low-income families [11], but its impact has not been evaluated. Here, we investigated the impact of socio-economic factors and the role of the economic status and education of mothers in particular, in the transmission of intestinal parasites in rural schoolchildren in two different Mexican regions.

ANCOVA analysis showed higher logarithms of the egg counts for A. lumbricoides and T. trichiura in the schoolchildren of Sinaloa than in Oaxaca (0.44 vs 0.17 and 0.99 vs 0.41 respectively) (p < 0.01). No difference was found in the intensities of H. nana between both states (p > 0.05).

Our study population provided data with 95% of confidence (expecting 50% of prevalence and 40% of non- participation) and was representative to populations with similar socio-economic status in the studied communities.

In this study, we looked at the prevalence of parasitic infections in schoolchildren in rural Mexican communities, and asked whether a number of socio-economic and environmental factors were related to the prevalence and intensity of infections. The intensities of A. lumbricoides and T. trichiura were statistically higher in the schoolchildren of Sinaloa than in those of Oaxaca. However, the prevalence of helminths infections was higher in the children of Oaxaca. It is known that environmental conditions are more conducive to development and transmission of helminths infections in Oaxaca, but the higher intensities found in Sinaloa may be associated not only to the environment conditions but also to re-infection rates, predisposition, or difference in the efficacy of the national albendazole administration.

Few epidemiological studies have been carried out in Sinaloa and Oaxaca, and those studies did not analyze the data according to demographic characteristics and socio-economic conditions. The present study revealed that the prevalences of G. duodenalis, E. coli, E. nana, I. butschlii, T. trichuria, A. lumbricoides, E. vermicularis, E. histolytica and H. nana in schoolchildren were similar to those found by Diaz et al. in 1987 and 1994 in the general population in rural and suburban communities in Sinaloa [16]. The low prevalence of A. lumbricoides in children from Oaxaca was probably a result of the albendazole given by the national campaign. The activity of a single dose of albendazole might be limited against protozoan parasites [17], but can improve cure rates and reduce egg counts of helminths such A. lumbricoides, hookworms, and T. trichiura [18].

We found that the prevalences of G. duodenalis, T. trichiura, E. coli, E. nana, and I. butschlii were higher than those reported in the general population of Oaxaca by Navarrete et al. in 1993 [19]. It is should be highlighted that protozoan infections, particularly those by G. duodenalis are an important cause of infection in these children.

No difference was found in the prevalence of infection between males and females in this study. Some studies have found a higher prevalence of particular parasites in females than in males, irrespective of age, such as in Papua New Guinea and in the Philippines where prevalence differences can be attributed to the different occupational activities of males and females [20, 21]. A higher family income was related to a lower prevalence of parasitism in the children in our study. Studies in Iran [22, 23]showed that the better the economic score of the family, the lower the prevalence of parasitic infection.

In this study, we asked whether toilet facilities and access to drinking water had an effect on rates of parasitic infection. Defecation in open areas was found to be associated with a higher risk of infection. This is in agreement with many earlier studies. In Panama, Holland et al. (1988) found that pit toilets or latrines reduced the risk of parasitic infection [24]. Prado et al. (2003) found that in Salvador, Brazil, a lack of a sewer in the house was significantly associated with G. duodenalis infection in 694 children aged from 2 to 45 months [25]. Properly functioning toilets installed inside the house reduced helminth infections in 319 individuals from Kuala Lumpur in Malaysia [26]. Proper hand washing and clean drinking water can reduce the transmission of helminth infections [27], and the type of drinking water (treated vs untreated) was significantly associated with intestinal parasitic infections in 551 individuals in Belize [28]. In our study safe drinking water and hand washing were not associated with infection. The latter might be explained by the inconsistency between what the parents said and what they really did in the household.

Prakash et al. (1980) [29] and Holland et al. (1988) [24] have highlighted that overcrowded conditions and particular types of house materials are associated with a high prevalence of parasitic infection. In this study, these factors were found not to be associated with infection. Most likely, the intra-family transmission of parasites is reduced by the national administration of albendazole, so that overcrowding does not have much impact on infection prevalence. Maternal, but not paternal, education levels were inversely correlated with the risk of infection in children in this study. This finding is in agreements with findings in studies in other developing nations. For example, Curtale et al., 1998 [10] found that the knowledge, perception, and behaviour of mothers were instrumental in designing and implementing an effective community-based intestinal helminth control program in Egypt. Wamani et al., 2004 [9] found that the mother's education was the best predictor of health and nutrition inequalities among children in rural Uganda. Finally, Nematian et al., 2004 [22] showed that the better the educational level of the mothers, the lower the parasitic infection rate in children in Iran. It is noteworthy that 55% and 45% of the fathers in the families from Sinaloa and Oaxaca respectively were absent from their homes for 6 months or more a year because of their employment. Maternal unemployment was a risk for infection in this study which is similar to data reported by Tucker in 1986 [30]. It would be expected that the more time mothers spend in the household, the better children's health. Sixty nine percent the mother in this study left children with grandmothers which could be related to a lower risk of parasitism.

There were no significant associations between the prevalence of protozoa or helminths with socio-economic factors which was probably due to the effect of dividing the sample into these categories. The same probably holds true for house materials, crowding index and type of drinking water.

In Egypt, there is increasing awareness in some communities about the importance of nutrition and hygiene education, especially for girls and mothers [10]. A community-based mothers' and infants' centre has been proposed to provide nutritional education and counselling for mothers from low income areas in Kota Emessu [31]. We propose that Mexican institutions should similarly promote health education to mothers in order to prevent and treat intestinal parasitic infections at home. Program managers and policy makers, as well as those running the Mexican national de-worming campaign, can more effectively target families with children at higher risk by targeting households in which the mother's educational levels are low. Such efforts will result in a direct and positive effect on the well-being of the young children.

Intestinal parasites still pose an important public health problem in the Mexican states of Sinaloa (north-western Mexico) and Oaxaca (south-eastern Mexico). The prevalence of helminth infection was higher in the schoolchildren from Oaxaca than that in those from Sinaloa in spite of the national anti-helminth campaign. Lower income, defecation in open areas, unemployment and low education level of mothers were the significant factors associated with these infections. Our results can be used by appropriate authorities to target vulnerable families in Mexican rural communities, and should encourage the involvement of mothers in the activities of the national deworming campaign because intestinal parasitic infections will be difficult to control by drugs alone.