Toxocara Seropositivity, Atopy and Wheezing in Children Living in Poor Neighbourhoods in Urban Latin American

Background Toxocara canis and T. cati are parasites of dogs and cats, respectively, that infect humans and cause human toxocariasis. Infection may cause asthma-like symptoms but is often asymptomatic and is associated with a marked eosinophilia. Previous epidemiological studies indicate that T. canis infection may be associated with the development of atopy and asthma. Objectives To investigate possible associations between Toxocara spp. seropositivity and atopy and childhood wheezing in a population of children living in non-affluent areas of a large Latin American city. Methods The study was conducted in the city of Salvador, Brazil. Data on wheezing symptoms were collected by questionnaire, and atopy was measured by the presence of aeroallergen-specific IgE (sIgE). Skin prick test (SPT), total IgE and peripheral eosinophilia were measured. Toxocara seropositivity was determined by the presence of anti-Toxocara IgG antibodies, and intestinal helminth infections were determined by stool microscopy. Findings Children aged 4 to 11 years were studied, of whom 47% were seropositive for anti-Toxocara IgG; eosinophilia >4% occurred in 74.2% and >10% in 25.4%; 59.6% had elevated levels of total IgE; 36.8% had sIgE≥0.70 kU/L and 30.4% had SPT for at least one aeroallergen; 22.4% had current wheezing symptoms. Anti-Toxocara IgG was positively associated with elevated eosinophils counts, total IgE and the presence of specific IgE to aeroallergens but was inversely associated with skin prick test reactivity. Conclusion The prevalence of Toxocara seropositivity was high in the studied population of children living in conditions of poverty in urban Brazil. Toxocara infection, although associated with total IgE, sIgE and eosinophilia, may prevent the development of skin hypersensitivity to aeroallergens, possibly through increased polyclonal IgE and the induction of a modified Th2 immune reaction

Acta Tropica

texto completo: acesso restrito. p. 46–51.Toxocara canis is a highly prevalent worldwide canine nematode responsible for enzootic and zoonotic infections. It is considered to be one of the main agents of human visceral and ocular larva migrans. False negative diagnosis may occur because adult infected dogs with “dormant” larvae may have negative fecal test results since they usually do not shed parasite eggs in their stools. During pregnancy, the larvae become active and infect the offspring through the placenta. A serological test can distinguish infected animals, thus increasing the accuracy of the diagnosis for epidemiological studies and prophylactic purposes. In the present work a serological investigation was carried out to study the risk factors for the acquisition of this infection in 301 dogs inhabiting the city of Salvador, northeast Brazil. A validated questionnaire was applied to the donors and caretakers to assess animal management practices. All dogs were submitted to clinical evaluation and blood collection. Serum samples were analyzed for IgG antibodies against excretory–secretory products of T. canis larvae, used as antigens, by indirect ELISA. The overall seroprevalence of antiT. canis IgG antibodies was 82.7%. Risk factors for T. canis infection included sex, area of origin within the city, homemade leftover food intake, failure to receive regular vaccination against infectious diseases and lack of preventive antihelminthic treatment. Most of these risk factors suggest a lack of veterinary care and poverty. The high frequency of seropositivity found for toxocariasis in dogs suggests that results based on parasitological fecal examination could underestimate the actual prevalence of the infection

The effect of single and multiple infections on atopy and wheezing in children.

The findings provide support for the idea that the hygiene hypothesis is operating in an urban Latin American context, but its expression is thus far restricted to the atopic status of patients and not the perceived asthma symptoms

Frequencies of the studied variables and their associations with anti-<i>Toxocara</i> IgG seroposivity in 1,148 children.

*<p>For at least one of the tested allergens.</p>**<p>Wheeze plus (i) diagnosis of asthma ever; (ii) wheezing with exercise in the last 12 months; (iii) ≥4 episodes of wheezing in the last 12 months; (iv) waking up at night because of wheezing in the last 12 months. Boldface numbers show those that are statistically significant at p<0.05.</p

Associations between anti-<i>Toxocara</i> IgG seropositivity and specific IgE (defined by (≥0.35 and ≥0.70 kU/L) and skin prick test (SPT) reactivity in 1,148 children.

#<p>For at least one of the tested allergens;</p>*<p>OR adjusted by gender, maternal schooling, parental asthma, mold, sewage system, infection by <i>A.lumbricoides</i> and <i>T. Trichuris</i>;</p>**<p>Shown are strata of optical densities to represent antibody levels; Boldface numbers show those that are statistically significant at P<0.05.</p