Cross-reactivity between sera from dogs experimentally infected with Dirofilaria immitis and crude extract of Toxocara canis

Canine filariasis in the Amazon: Species diversity and epidemiology of these emergent and neglected zoonoses

Dirofilaria immitis and Acanthocheilonema reconditum are common parasites in dogs but have also been reported parasitizing humans. The differential diagnosis and epidemiological evaluation of these zoonoses are important to the development of efficient public health policies and control strategies. The purpose of this study was to carry out an epidemiological survey by using molecular methods for the specific identification of filarid parasites of domestic dogs in the Marajó mesoregion, State of Pará (PA), Brazil. A total of 418 canine blood samples from Marajó mesoregion (Northern Brazil) were collected, submitted to DNA extraction, polymerase chain reaction (PCR) with “pan filarial” primer, subsequent sequencing and sequence analysis using BLASTn software comparison with previously deposited sequences in GenBank. After that, a phylogenetic analysis by Maximum Parsimony was performed to aid the specific diagnosis. The obtained sequences showed the occurrence of 9 (2.15%) dogs infected with D. immitis and 30 (7.18%) by A. reconditum, with a confidence interval of 95%, there were no cases of co-infection. We observed that male dogs were more likely to D. immits and A. reconditum infection. However, age was not significant to both infections. This study reports for the first time the occurrence of A. reconditum in the northern region of Brazil and confirmed the presence of D. immitis in the Marajó mesoregion.

Heat treatment and false-positive heartworm antigen testing in ex vivo parasites and dogs naturally infected by Dirofilaria repens and Angiostrongylus vasorum

Background

Heartworm antigen testing is considered sensitive and specific. Currently available tests are reported as detecting a glycoprotein found predominantly in the reproductive tract of the female worm and can reach specificity close to 100%. Main concerns regard sensitivity in the case of light infections, the presence of immature females or cases of all-male infections. Research and development have been aimed at increasing sensitivity. Recently, heat treatment of serum prior to antigen testing has been shown to result in an increase in positive antigen test results, presumably due to disruption of natural antigen–antibody complexes. Cross-reactions in dogs with both natural and experimental infections with Angiostrongylus vasorum and Spirocerca lupi have been reported, but cross-reactions with other helminths have not been extensively studied. In order to evaluate potential cross-reactivity with other canine and feline parasites, two studies were performed. Study 1: Live adults of Dirofilaria immitis, Dirofilaria repens, Toxocara canis, Toxocara cati, Dipylidium caninum, Taenia taeniaeformis and Mesocestoides spp. larvae were washed and incubated in tubes with saline solution. All worms were alive at the time of removal from the saline. Saline solutions containing excretory/secretory antigens were then tested for heartworm with six different, commercially available antigen tests. All results were evaluated blind by three of the authors. Study 2: Sera from dogs with natural infections by A. vasorum or D. repens, living in areas free of heartworm disease, were tested with the same tests before and after heat treatment (103 °C for 10 min).

Results

Results suggest that antigens detected by currently available tests are not specific for D. immitis. They may give positive results through detection of different parasites’ antigens that are normally not released into the bloodstream or released in a low amount and/or bound to antibodies. Tests may even detect antigens released by male D. immitis adult worms. D. repens appears to release more detectable antigens than the other worms studied.

Conclusions

Cross-reaction with A. vasorum and D. repens does occur in the field and could potentially occur with other helminths. Heat treatment decreases specificity by enhancing cross-reactivity.

Relevance of eosinophilia and hyper-IgE in immigrant children

Immigrants from undeveloped countries are a growing problem in Europe. Spain has become a frequent destination for immigrants (20% of whom are children) because of its geographic location and its historic and cultural links with Africa and Latin America. Eosinophilia is frequent in adult immigrants, travelers and expatriates coming from tropical areas. However, there are few studies that focus on the incidence and causes of tropical eosinophilia and hyper-IgE in immigrant children.We evaluated, prospectively, the prevalence and causes of eosinophilia and hyper-immunoglobulin E (IgE) in 362 immigrant children coming from Sub-Saharan Africa, Northern Africa and Latin America to Salamanca, Spain, between January 2007 and December 2011.Absolute eosinophilia and hyper-IgE were present in 22.9% and 56.8% of the analyzed children, respectively. The most frequent causes of absolute eosinophilia were filariasis (52.6%), strongyloidiasis (46.8%) and schistosomiasis (28.9%). Filariasis (41.9%), strongyloidiasis (29.6%) and schistosomiasis (22.2%) were the most frequent causes of increased levels of IgE. The area under the ROC curve showed similar values between eosinophil count and IgE levels in the diagnosis of helminthiasis (69% [95% confidence interval (CI) 63%-74%] vs 67% [95% CI 60%-72%], P = 0.24). Eosinophilia and hyper-IgE have a high value as biomarkers of helminthiasis in children coming from tropical and subtropical areas.