Epidemiology of bovine viral diarrhoea among tropical small holder dairy units in Kerala, India
Vinodkumar Kulangara & Anumol Joseph & Nandu Thrithamarassery &
Asok Sivasailam & Latheef Kalappurackal & Saranya Mattappillil &
Radhika Syam & Saseendranath Mapranath
Received: 7 July 2014 /Accepted: 12 January 2015 # Springer Science+Business Media Dordrecht 2015
Abstract Prevalence of bovine viral diarrhoea among 385 dairy cattle reared under a small holder system in Trichur
District of Kerala State in India was determined through an
ELISA targeting antibodies against p80-p125 non-structural protein of the virus. Prevalence was 24.7 % among the total population, but was higher (52 %) when 85 animals having infertility problems alone were considered. Significant serum biochemistry differences between animals could be noticed only in total protein, globulin and phosphorous, all of which were low in seropositive animals. All animals which were seronegative for antibodies were screened by another ELISA targeting the Erns protein of the viral nucleocapsid to detect persistently infected (PI) animals. The single, positive animal had only a transient period of antigens in the blood, indicating absence of PI animals in the study population. High prevalence of the disease in isolated small holder units even in the absence of PI animals is discussed in view of identifying the common source of infection and initiating control measures.
Keywords BVD . Small holder systems . Prevalence .
Bovine viral diarrhoea (BVD) is an economically important disease of dairy cattle all over the world. Magnitude of the incidence of BVD is often unappreciated because 70–90 % of infections result in subclinical presentation only (Neibergs et al. 2011). Seroprevalence of the disease among tropical countries has been reported (Mishra et al. 2011), but detailed reports on actual epidemiology of the disease on the small holder dairy systems of the tropics are lacking. Acute clinical forms of BVD, including mucosal disease, have not yet been reported in India so far, but seroprevalence was detected in samples randomly collected from different parts of the country (Behera et al. 2011). Existence of the disease among cattle (Sood et al. 2007), sheep, goats (Mishra et al. 2009) and buffaloes (Mishra et al. 2008) in India has been confirmed through molecular methods.
Persistently infected (PI) animals are considered to be the key mode by which the virus maintains and perpetuates itself in the cattle population (Broderson 2014). PI animals are the result of in utero infection by the non-cytopathic biotype of BVD virus during the period of fetal development from gestation day 45 to gestation day 125, leading to immunotolerance (Hessman et al. 2012). They shed large quantities of virus throughout their short lifetime, becoming the major source of virus spread both within and between farms (Goyal and Ridpath 2005). Since the PI animals remain serologically negative for antibodies against homologous bovine viral diarrhoea virus (BVDV), but positive for BVD antigen, different assays targeting viral antigens are preferred for their detection in a herd. Among the two methods of antigen
ELISA, specificity of indirect ELISA is generally hampered by secondary sera contamination (Houe et al. 2006), and hence, monoclonal antibody-based competition ELISA is preferred for testing of suspected PI animals for BVD Erns antigens (Yan et al. 2011). High level of sensitivity is the primary
V. Kulangara (*) :A. Joseph :N. Thrithamarassery :
A. Sivasailam : L. Kalappurackal : S. Mattappillil :R. Syam :
Department of Veterinary Epidemiology and Preventive Medicine,
Kerala Veterinary and Animal Sciences University, Mannuthy,
Trichur, Kerala, India e-mail: firstname.lastname@example.org
Haritha, Mukkattukara, Nettissery (PO), Trichur, Kerala 680657,
Trop Anim Health Prod
DOI 10.1007/s11250-015-0766-y requirement of a serological screening test for BVD. Humoral immune response allows detection of antibodies against the structural envelope proteins E2 and Erns, as well as the highly conserved non-structural protein NS3 (p80 in non-cytopathic and p125 in cytopathic types) (Mishra et al. 2010). Among these, NS3 protein is considered as the antigen of choice and is used in commercial kits for detection of BVDVantibodies in cattle.
Determining the regional epidemiology of BVD in view of prevailing animal husbandry practices in an area will help in designing control programmes sui table for each region (Bachofen et al. 2008). Central component of BVDV control in the intensively managed herd systems of developed countries is the identification and elimination of PI animals that are the major reservoir of the virus (Bachofen et al. 2013).
Epidemiology of BVD among small holder dairy units of tropical countries varies because the isolation and smaller size of individual units may preclude exposure to PI animals. This study was undertaken to determine the prevalence of BVD among dairy cattle reared under typical small holder dairy units common in the tropics and to identify the source of infection for designing future control strategies against the disease.
Material and methods
Seventy-five small holder dairy units located in an area of approximately 100 km2 in Thrissur District, Kerala State,
India, were selected at random for the study. Total cattle population in the area was 2094 as per the 2008 census of Kerala
State Animal Husbandry Department. The entire population of 282 dairy cows/heifers and 18 calves belonging to these 75 dairy units (average strength 3.4 animals) and another 85 animals from similar units which were brought to the infertility camps conducted by State Animal Husbandry Department in the area for expert evaluation and treatment were included in the study. History of occurrence of any major disease during the past year was collected. Health status of animals at the time of screening was assessed by clinical examination and laboratory evaluation of haematological and biochemical parameters.