Elsevier

Veterinary Parasitology

Volume 173, Issues 1–2, 11 October 2010, Pages 139-142
Veterinary Parasitology

Short Communication
Seroprevalence of Neospora caninum in gray wolves in Scandinavia

https://doi.org/10.1016/j.vetpar.2010.06.006Get rights and content

Abstract

Transmission of the protozoan parasite Neospora caninum between wild and domestic animals has gained some interest during recent years. Because of the close relationship between gray wolf (Canis lupus) and dog it has been suggested that gray wolf is a definitive host for the parasite. The aim of this study was to estimate the seroprevalence of N. caninum in Scandinavian gray wolves and to investigate any geographical patterns of the infection. The investigation was based on blood samples collected from 109 wolves between 1998 and 2009 within the Scandinavian wolf project Skandulv. They were analysed by N. caninum iscom ELISA and those with absorbance values exceeding 0.20 were also analysed by immunoblotting. Samples that were positive in both tests were deemed positive. Four (3.7%) wolves were positive at the first sampling. They were all sampled 2005 at different locations, and were both females and males. From one male wolf three samples were collected over a 7-year period. No antibodies were detected at the first sampling in 1998 when he was approximately 8 months old but when he was sampled again 5 and 7 years later the ELISA and immunoblotting were positive. The results indicate that N. caninum infection is present in Scandinavian wolves. It is unclear how the wolves acquired the infection.

Introduction

Neospora caninum is a protozoan parasite that was first described in dogs where it may cause paralysis of the hind limbs, ascending paresis, dermatitis, and other clinical symptoms (Buxton et al., 2002). Today it is also recognised as an important cause of bovine abortion (Dubey, 2003). N. caninum has a two-host lifecycle with dogs and coyotes (Canis latrans) as definitive hosts that can excrete oocysts in the faeces after ingestion of tissues from an infected intermediate host (McAllister et al., 1998, Gondim et al., 2004b). Many mammalian species can act as intermediate host for the parasite. Presence of N. caninum specific antibodies in blood indicates that the animal is, or has recently been, infected with the parasite (Björkman et al., 2007).

N. caninum infection in wildlife was first reported in 1994 when the parasite was identified in a black-tailed deer (Odocoileus hemionus columbianus) that had been found dead in California (Woods et al., 1994). Since then, serological evidence of N. caninum infection has been found in other wild herbivores, e.g. chamois (Rupicapra rupicapra), moose (Alces alces), red deer (Cervus elaphus), roe deer (Capreolus capreolus) and white-tailed deer (Odocoileus virginianus) (Dubey et al., 1999, Ferroglio and Rossi, 2001, Gondim et al., 2004a) but infection has not been proven by demonstration of the parasite. There is an ongoing discussion concerning the possibility that other wild canids than the coyote might serve as definitive hosts for N. caninum. Because of the very close relationship between the gray wolf (Canis lupus), the domestic dog, and the coyote, the gray wolf has been a top candidate as definitive host, and serological investigations indicate that they can be infected with the parasite (Gondim et al., 2004a, Dubey and Thulliez, 2005).

In Sweden, clinical disease associated with N. caninum has been reported in both dogs and cattle (Uggla et al., 1989b, Stenlund et al., 1997). Surveys have shown that 2% of the Swedish dairy cattle are infected with N. caninum and that 8% of the dairy herds house infected cows (Björkman et al., 2000, Frössling et al., 2008). The infected herds are not evenly distributed over Sweden but the prevalence is higher in the central parts of the country (Frössling et al., 2008). No demographic or other factors that might explain these regional differences have yet been identified, but it has been noticed that the high risk area for N. caninum infection in dairy cattle is located in a region which is inhabited by wolves.

The wolves in Sweden and Norway are members of a joint Scandinavian wolf population (Skandulv, 2009). After being nearly extinct in the beginning of 1970, the numbers have gradually increased and in the winter 2008–2009, the population was estimated at 213–252 individuals (Wabakken et al., 2009). The majority, 177–194 individuals in 2008–2009, live in family groups (packs) or pairs but there is also both migrating and stationary solitary wolves. The highest densities of wolves are found in south-central Sweden extending into Norway (58°2″–62°24″ N; 11°30″–16°43″ E).

The aim of this study was to estimate the seroprevalence of N. caninum in Scandinavian gray wolves and to investigate any geographical patterns of the infection.

Section snippets

Animals and samples

Blood samples used in this study were collected as part of the Scandinavian wolf monitoring project (Skandulv, 2009). Every winter since 1998–1999, wolves have been chemically immobilized for radio collaring, health assessment and collection of biological material. Some individuals have been captured several times to change the radio collar. Blood samples were collected from the cephalic vein, kept at room temperature for 1–2 h and then centrifuged at 1500 × g for 10 min. Serum was then separated

Results

Six of the 109 investigated wolves had serum samples with iscom ELISA COD  0.20 at the first sampling. Samples from four of the wolves were positive also in immunoblotting giving a N. caninum seroprevalence of 3.7% (95% CI: 0.1–7.2%). These seropositive animals were sampled in winter 2004–2005 in different packs. Twelve wolves were sampled for the first time this winter. Two of the seropositive wolves were males and two were females, and they were between 8 months and 5 years old (Table 1).

Discussion

The results of the present investigation indicate that N. caninum infection is present in Scandinavian wolves. It is unclear how the wolves in this study may have acquired the infection. Although we have not investigated presence of the parasite in prey species in this area, serological surveys indicate that N. caninum is very rare among Swedish wildlife. In a recent study comprising 417 moose sera collected from all over Sweden, all samples were negative (Malmsten et al., unpublished results).

Conflict of interest statement

The authors declare that they have no competing or conflicting interests.

Acknowledgement

We are grateful to Skandulv for giving us access to serum samples and information about the wolves included in this study.

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