Neospora caninum is a protozoa that causes abortion and economic losses in cattle worldwide.1 In cattle, transplacental transmission is the main mechanism by which the parasite persists in a herd.2 After recognizing the dog as the definitive host of the parasite, epidemiological work established the association between the presence of dogs and the disease in cattle.3,4 Additionally, the association of canids with cattle on their premises, has been postulated as a risk factor for the disease.5 Similarly, it has been established that intensive herd management was associated with increased seroprevalence to N. caninum.6 The presence of wild canids have also been related with high prevalence of sero-active cattle.7 Neosporosis of cattle has been associated with abortion, neonatal mortality and decrease in the volume of milk production that cause yearly economic loss.8
The seroprevalence of N. caninum infection in cattle varies largely, depending on the country and region.8 Several assays are available for detecting antibodies to N. caninum in cattle.9,10 Some serological studies in dairy herds have done in some part of Iran. However, there is not published information of N. caninum infection in the cattle of this province.
This study was performed to determine the prevalence of antibodies to N. caninum in industrial dairy cattle in Hamedan province, using enzyme-linked immuno-sorbent assay (ELISA).
Materials and Methods
A cross-sectional study was performed in the first half of year 2010. Blood samples were taken from 492 dairy cattle in the 41 industrial farm of Hamedan province, Iran. The animals were randomly selected. The owners were questioned about age, breeding, dog presence and its contact with the herds, abortion history, and herd population.
All samples were immediately transported to the diagnostic laboratory of Hamedan Veterinary Office, Hamedan, Iran. Serum was removed after centrifugation at 1000 g for 15 min. All sera were stored at -70 ˚C until laboratory testing.8
The samples were analyzed for antibodies against N. caninum using ELISA kit. Anti-Neospora antibodies were detected using a commercially available N. caninum ELISA kit (Herdcheck, Maine, USA). The kit was used according to the manufacturer’s instructions. The presence or absence of antibody was determined by calculating of sample to positive ratio (S/P ratio according to the formula mentioned inside the manual). A S/P ratio more than 0.5 and less than 0.5 was considered positive and negative, respectively.
Immunoglobulin G (IgG) antibodies to N. caninum were found in 63 of 492 (12.80%) sera (CI = 0.12 ± 0.03). With regard to seropositivity, significant differences were found regarding herd population (X2 = 13.15, df = 1.00 and p < 0.001), abortion history (X2 = 48.06, df = 1.00 and p < 0.001), dog presence in farm (X2 = 9.45, df = 1.00 and p = 0.002), dog contact with herd (X2 = 5.73, df = 1.00 and p = 0.01); and stray canids presence in farm (X2 = 37.17, df = 1.00 and p < 0.001). There were no significant differences between seroprevalence and age (X2 = 3.96, df = 3.0 and p = 0.262), as well as breeding (X2 = 0.88, df=1.00 and p = 0.346), (Table 1).
This study was the first report of N. caninum infection in industrial dairy cattle in Hamedan proviance. There were only a few reports on N. caninum seroprevalence in dairy cattle of Iran.10-13 The seroprevalence rate were reported 32.00% in Babol (north of Iran), 46.00% in Mashhad (northeast of Iran) and 12.60% in Kerman (southeast of Iran) using ELISA.10-12 The similar rate of infection was reported in Brazil, Greece, Peru, Australia, Canada, Ireland, Korea and Spain. 3,9,14
In the present study, the herd seroprevalence was similar to that study in Thailand and different to other countries.3,13 Difference of management in farms, study design and sample size are main cause of varied results.
In current study, there was no significant difference in seroprevalence between the different age groups which was similar to result of Nourollahi et al. in Kerman and other researchers.9,10,15-18 Razmi et al. reported statistically significant in different age groups.12 Sadrebazzaz et al. and Wouda et al. reported equal levels of seroprevalence in all age groups for most herds.13,19 Jensen et al. suggested seroprevalence increased with age and depended on sample size.20 Lower seroprevalence in cattle of > 2 age is due to a decrease of antibody in congenital infections. It seems relationship between age and seroprevalence rate is speculative.
In a French study, similar to our study, there was not association between seropositivity and breed.21 The prevalence of N. caninum in dairy cattle was reported higher than beef cattle in Spain.22,23 This might be related to different production systems for dairy and beef cattle rather than to breed differences. Comprehensive research on the impact and role of different breed in the prevalence of infection is essential.
In this study, there was a 2.70 fold increase of seroprevalence in farms with more than 100 individuals [p = 0.0005, OR = 2.70(1.55-4.70)]. Kyaw et al., reported that cattle in larger farms (≥ 21) had a higher infection than small herds (< 21) in Thailand, (p = 0.03); opposite to Davison et al. study.17, 24
In a study in Italy, the risk of seropositive case increased with the herd size due to increasing number of dogs.25 Our results provide strong support for the hypothesis that increase of herd capacity is a risk factor of Neospora infection.
In present study, 57.10% of cattle with abortion history were seropositive (p = 0.0005). Razmi et al. reported, that the abortion prevalence in seropositive cattle was higher than seronegative (p < 0.05, OR = 1.78) in Mashhad.12 This is similar to our and other results.2,3,9,18 Evaluation of seropositivity in previous studies showed that the risk of abortion were 4.00, 5.30 and 8.00 fold higher than seronegative cattle.26-29 Our result taken together with previous investigations supports the notion that the seropositivity rate is correlated with abortion.
In current study, N. caninum infection was reported 10.00% (36/360) in the farms with dog presence [p = 0.002, OR = 0.43(0.25-0.74)]. However, 13.50% (26/122) of cattle in contact with dog were seropositive. A 2.47 fold increase in the rate of infection was observed in cattle with dog contact [p = 0.02, OR = 2.47(1.16-5.30)]. Around 27.00% (39/144) of cattle in contact with stray canids (fox and jackal) were seropositive (p = 0.0005).
Studies in Spain and France have also found positive associations between the seropositivity of cattle and the presence or the number of farm dogs.21 Barling et al. observed the presence of dog in farms was a putative protectivefactor.30 Our result is the opposite of Kyaw et al. finding.17
The presence of dogs in farm has been assumed to provide the greatest chance of horizontal transmission through the ingestion of oocysts shed by infected dogs. In addition, dogs kept in the neighborhood farmsmay pose an infection risk.
The results of this research can provide baseline information for the future studies. There are both horizontal and vertical transmissions of N. caninum in Hamedan province. Therefore, evaluation of Neospora infection in other intermediate hosts and also definitive hosts are necessary for control strategies.
In conclusion, N. caninum is an important factor of economic loss in industrial dairy cattle in Hamedan province. Therefore, it warrants a complete overhaul of management in dairy farms.
This study was supported financially by Veterinary Office of Hamedan, Iran. We greatly thank Dr. Gholamreza Tavoosidana and Dr. Hesameddin Akbarein for their kind help.