Red foxes (Vulpes vulpes) are a natural intermediate host of Neospora caninum

Abstract

The present study was undertaken to determine if red foxes are natural intermediate and/or definitive host for Neospora caninum and to study the importance of infection of N. caninum in this species in North-eastern Spain. Faecal samples and brain tissues were obtained from 122 foxes from 21 rural areas of Catalonia. Faeces collected were examined for parasite eggs and coccidian oocysts using sucrose flotation. For PCR-based diagnosis of N. caninum in brain tissues, the specific genomic Nc5 region was selected as the target sequence for DNA amplification. To control for PCR failure and facilitate identification of truly negative samples, the competitor pNc5C molecule was added to all negative samples in a second round of PCR reactions. Of the 122 foxes analysed, 13 (10.7%) were positive by PCR for N. caninum. Signal intensities of all positive samples were relatively weak with the exception of one sample from a 3-month male animal, that also showed the highest repeatability. No differences were observed by sex, age or area of sampling analysis. Detection of stages of N. caninum in brain from naturally infected red foxes demonstrated that red foxes are a natural intermediate host for N. caninum. Faecal samples were analysed for the presence of N. caninum oocysts, however, no oocysts compatible with N. caninum were found. A widespread latent infection of red foxes in North-eastern Spain found in the present study indicates that red foxes could have a very important role in the epidemiology of neosporosis in our area.

Introduction

Neospora caninum is an obligate intracellular protozoan parasite which can infect domestic and wild canids, ruminants and horses (Dubey and Lindsay, 1996). The parasite was first described as causing paralysis and death in dogs, and has recently gained considerable attention, due largely to its impact of economical losses on the dairy industry by reproductive failure associated with abortion (Dubey and Lindsay, 1996). Domestic dogs are the only proven definitive host and excrete N. caninum oocysts in their faeces (McAllister et al., 1998; Lindsay et al., 1999a, Lindsay et al., 1999b). Since the definitive host was reported, the epidemiological role of carnivorous wildlife, especially wild canids such as red foxes, has become increasingly important. N. caninum antibodies have been found in coyotes (Lindsay et al., 1996), dingoes (Barber et al., 1997), and red and grey foxes (Barber et al., 1997, Buxton et al., 1997, Simpson et al., 1997, Barling et al., 2000, Lindsay et al., 2001, Schares et al., 2001) suggesting a role for wild canids in the epidemiology of neosporosis. Furthermore, reports have also established that deer, a natural prey of wild canids, are a natural host for N. caninum (Woods et al., 1994, Dubey et al., 1999) and it is plausible that a sylvatic transmission cycle for neosporosis exists (Barling et al., 2000, Lindsay et al., 2001).

Red foxes are the main wild canids in Spain. Previous studies have documented the occurrence of antibodies to N. caninum in red foxes (Barber et al., 1997, Buxton et al., 1997, Simpson et al., 1997, Schares et al., 2001), however we are unaware of any previous study to determine the presence of N. caninum in tissues of naturally infected red foxes. The present study was undertaken to determine if red foxes are a natural intermediate host for N. caninum by direct detection of the parasite using PCR in brain tissues and to determine if red foxes are a definitive host by analysis for the presence of N. caninum oocysts in faecal samples.