Dog echinococcosis in northern Spain: Comparison of coproantigen and serum antibody assays with coprological exam

Abstract

A large sheep-dog population from the province of Álava (northern Spain) has been investigated in order to determine the prevalence of the cestode parasite Echinococcus granulosus. Worms were detected in 14.0% of 721 dog faecal supernatants by coproantigen ELISA, and in 9.1% of 754 dog serum samples by serum antibody ELISA. A weak but statistically significant correlation (Spearman's ρ = 0.103, 95% CI: 0.023–0.178) between the two immunoassay results was found. In addition, eggs of the family Taeniidae were detected in 10.3% of 726 faecal samples examined by coproparasitological (flotation and sedimentation) tests. The overall E. granulosus infection rate, based on a Bayesian latent class model that accounts for the imperfect sensitivities and specificities of all diagnostic tests used, was estimated to be 8.0% (95% credible interval: 5.4–11.4%), corroborating that sheep-dog is the dog class most vulnerable to acquiring the infection. Dog sex did not influence the prevalence of E. granulosus, independently of the diagnostic test used or the dog region of origin. No significant linear correlation was found between the coproantigen ELISA OD values and the dog age (Spearman's ρ = −0.049, 95% CI: −0.234 to 0.135), suggesting that there were no differences in prevalence of E. granulosus between old and young dogs. The obtained results highlight the importance of initiating a control program based on regular treatment of the sheep-dogs with praziquantel in the province of Álava.

Introduction

Cystic echinococcosis (CE) is an important zoonosis caused by the taeniid tapeworm Echinococcus granulosus with a considerable impact in both human and animal health in endemic areas (Schantz et al., 1995). The disease has a wide geographical distribution, with emerging and re-emerging regions mainly in Central Europe and China (Eckert and Deplazes, 2004). Spain, together other Mediterranean countries, is currently considered as hyper endemic area (McManus et al., 2003).

The parasite's domestic life cycle is maintained through dogs (which harbour the adult tapeworm) and a range of domestic livestock intermediate host species, generally sheep and cattle. Due to the high biotic potential of E. granulosus, infected dogs can excrete a large number of parasite's eggs with their faeces, contaminating wide extensions of soil, and spreading the disease (Gemmell, 1990). Because its pivotal role in the transmission dynamics of CE, detection of E. granulosus in the definitive host is a key point in developing of epidemiological studies and implementation of hydatid control programmes in endemic areas (WHO/OIE, 2001).

Necropsy of dogs and examination of the small intestine is the reference method for the detection of intestinal infections with E. granulosus, but this laborious and ethically questionable procedure is not suitable for mass screening. Thus, a number of antemortem methods have been developed for diagnostic purposes. Arecoline purging, although 100% specific, has a highly variable sensitivity (a negative result even after two or more treatments does not guaranteed the animal is Echinococcus-free), is labour intensive, biohazardous and some dogs suffer undesired side-effects (Wachira et al., 1990, Eckert et al., 1984, Eckert et al., 2001). Coprological exams have low specificity and sensitivity, as eggs from different taeniid cestodes cannot be differentiated by light microscopy, and egg production may be erratic. Finally, ELISAs for detecting parasite-specific antibodies in serum have showed variable sensitivities, ranging from 40 to 90% (Benito et al., 2001, Gasser et al., 1994, Jenkins et al., 1990), and cross-reactivity with other parasite species is often detected (Gasser et al., 1988).

Currently the most practical approach for the diagnosis of the intestinal E. granulosus infection in dogs is the detection of parasite antigens in faecal samples (coproantigens) by ELISA using antibodies against adult somatic antigens (Allan et al., 1992), and excretory–secretory products from proglottids (Deplazes et al., 1992) or protoscoleces (Benito and Carmena, 2005). This method considerably improves both diagnostic sensitivity and specificity, permits the detection of the parasite during the prepatence period (Ahmad and Nizami, 1998), shows the current status of the infection (Jenkins et al., 2000), and ELISA results correlate well with the worm burden in the dog intestine (Craig et al., 1995). Coproantigen ELISAs have been successfully used in the field in Libya (Buishi et al., 2005), Cyprus (Christofi et al., 2002), Uruguay (Malgor et al., 1997), and Wales (Palmer et al., 1996), demonstrating their usefulness for epidemiological studies.

Recent field surveys have shown that sheep and stray dogs have the highest E. granulosus infection rates, most likely because of their greater access to offal or casualty animals (Buishi et al., 2005, Shaikenov et al., 2003). Therefore, those are the dog classes currently considered to be at highest risk of infection by this cestode. In the province of Álava (northern Spain) we have previously reported similar parasitological findings (Benito et al., 2003), although most of the dogs analyzed in that study came from urban environments. In this paper we present data on the detection of E. granulosus in a large population of sheep-dogs from the same region, by using ELISAs for the detection of parasite-specific coproantigens and antibodies, and coproparasitological examination.