Recent advances in Neospora and neosporosis

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Abstract

Neospora caninum has emerged as a major cause of abortion in cattle in many countries. This paper reviews recent advances in the life cycle and biology of Neospora with the emphasis on bovine neosporosis. The role of the recently discovered oocyst stage of N. caninum in the epidemiology of neosporosis is discussed. Progress made in serologic diagnosis of N. caninum infection is discussed. There is no vaccine for preventing Neospora-induced abortions in cattle or to prevent oocyst shedding in dogs.

Introduction

Neosporosis has emerged as a serious disease of cattle and dogs during the last five years. Since the first recognition of the disease in 1984 (Bjerkås et al., 1984) and the description of the new genus Neospora and the type species N. caninum (Dubey et al., 1988a), over 250 publications have appeared in the literature. An earlier review in 1996 covered its history and biology in detail, and listed 193 references (Dubey and Lindsay, 1996). Therefore, in the present paper most of the references prior to 1996 are not repeated. In this review, recent advances in the life cycle and biology of Neosporaare discussed, with the emphasis on bovine neosporosis.

Section snippets

Life cycle and general biology

Neospora caninum is the type species of the genus. Recently, another species, N. hughesi has been proposed for the parasite in the horse (Marsh et al., 1998); it will be discussed under the section on neosporosis in horses. The predicted coccidian nature of the parasite was recently confirmed (Fig. 1) when its oocyst was found in dog feces (McAllister et al., 1998a). Thus, dogs can serve both as intermediate and definitive hosts. In addition to dogs, cattle and horses discussed in this review,

Prevalence

Neospora caninum affects both dairy (Dubey and Lindsay, 1996) and beef cattle (Hoar et al., 1996, Waldner et al., 1998). It is a major cause of abortion in dairy cattle in the U.S. (Anderson et al., 1991, Anderson et al., 1995), New Zealand (Thornton et al., 1991), and the Netherlands (Wouda, 1998). Recently, bovine N. caninum infection has been reported from Argentina (Campero et al., 1998 ); Belgium (de Kruif et al., 1997); Canada (Duivenvoorden and Lusis, 1995, Pare et al., 1998); Denmark (

Equine neosporosis

Neospora infections have been reported from an aborted foal (Dubey and Porterfield, 1990), a congenitally infected foal (Lindsay et al., 1996b), a 10-year-old horse (Gray et al., 1996), a 19-year-old horse with Cushing’s disease (Daft et al., 1996), a 20-year-old horse with pituitary tumor (Hamir et al., 1998) and an 11-year-old Quarter Horse gelding (Marsh et al., 1996). Neospora organisms were isolated from the 11-year-old horse and described as a new species, N. hughesi, based primarily on

Prevalence and distribution

A recent serological survey in Japan reported a higher prevalence of N. caninum infection in dogs on dairy farms with abortions (31% of 48 dogs) compared with dogs from urban areas (7% of 198) (Sawada et al., 1998). Sera were screened at a 1 : 50 dilution in IFAT. In the most comprehensive survey reported so far, Barber et al. (1997a) tested 1554 dogs from three continents for N. caninum antibodies at a 1 : 50 dilution in the IFAT. The seroprevalences were 9% of 451 dogs in Australia; 20% of 414

Acknowledgements

I would like to thank Drs. Gereon Schares for preparing Table 1, Susan Liddell for preparing Table 2, and Andrew Hemphill, Mark Jenkins, Julie Paré, Arvid Uggla, and Willem Wouda for helpful suggestions.

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