Seroprevalence of antibodies and diagnosis of abortion related to neospora caninum in dairy cattle

Abstract

The seroprevalence of antibodies to neospora caninum (NC) and the relationship between seropositivity and age (heifer vs. cow), and the relationship of herd infection with herd size and with presence of dogs on the farm in dairy cattle were studied involving 549 cows and 82 dogs in 59 dairy herds in Nakhon Pathom. A competitive enzyme-linked immunosorbent assay (c-ELISA) was used to detect the NC-antibodies in the sera. Individual and herd seroprevalence of NC were 5.46% (30/549) and 33.9% (20/59) respectively. No significant associations of NC seropositivity with age of cow (heifer vs. cow; p=0.331) and of herd infection with the presence of dogs on the farm (p=0.378) were observed. The larger herd (>=21 cows) had significantly higher infection (p=0.034) than small herds (>=20 cows). Of 12 cows with abortion history, one was seropositive to NC. Seroprevalence of NC antibodies in dogs was 1.2% (1/82). This is the first NC seroprevalence study in dogs in Thailand. It was concluded that Neospora-infection was common in herd rather than individual level in Thailand and the presence of dogs on the farm was not always related to the herd infection and caution should be taken in the interpretation of serological tests from the farm dogs. An immunohistochemical (IHC) examination was conducted to detect NC organisms in 12 aborted fetal tissues (3-8 months gestation) collected from 2 farms in Saraburi and Chonburi Provinces. Five of these cows (41.7%) were seropositive to NC. Neospora-tachyzoites were detected in the placenta of a seropositive cow aborted at 4 months of gestation. Neither the NC parasites nor tissue cysts were detected in the other fetal tissues. Also, 38.5% (5/13) of cows whose aborted fetuses were not collectable were seropositive to NC. This is the first report on the identification of NC parasite in Thailand. It was concluded that the identification of Neospora-parasite and high percentage of Neospora seropositivity in the aborting cows strongly indicated the possibility of NC as a major cause of abortions and it is important to make further studies for the control measure of this disease.