Bluetongue disease is an arthropod-transmitted viral disease of ruminants with a worldwide distribution. Bluetongue outbreaks has been reported among livestock in Malaysia during the 1990s and since then few studies have paid attention to the status of Bluetongue in Malaysia. The aim of this study was to determine the seroprevalence of antibodies to bluetongue virus among goats in selected small ruminant farms in Selangor, Malaysia. Blood samples were collected from 100 randomly selected goats. Sera were harvested and used for antibody detection. The result obtained revealed that all the samples tested were negative for antibodies to bluetongue virus. It was concluded that the goats sampled in this study were not exposed to bluetongue virus. Further studies using a bigger sample size, multiple species and a larger study area will be required to elucidate on the epidemiology of bluetongue virus in livestock of Malaysia.
Bluetongue disease is an arthropod-transmitted viral disease of ruminants with a worldwide distribution and of great economic significance (Maclachlan, 2011). The disease is caused by Bluetongue virus (BTV), a member of the Orbivirus genus in the Reoviridae Family (Mintiens et al., 2008; Chatzopoulos et al., 2015). Transmission of this disease is usually by biting midges belonging to the Culicoides genus (Mintiens et al., 2008; Andriamandimby et al., 2015) although direct vertical transmission between animals is possible (Chatzopoulos et al., 2015). Bluetongue spreads rapidly among livestock resulting in significant effect on their well-being (Mozaffari et al., 2014). Clinical signs of bluetongue disease vary among species but generally, fever, serous bloody nasal discharges, oedema, erosion and ulcers are the predominant clinical signs of bluetongue disease in small ruminants (Shoorijeh et al., 2010; Chatzopoulos et al., 2015). Cattle and other ruminants may have ocular discharges, conjunctivitis, oral mucosal congestion ulceration of the muzzle and teats when infected with BTV (Andriamandimby et al., 2015). The impact of bluetongue disease is quite significant as outbreaks may disrupt trade of animals and animal products (Mintiens et al., 2008). In non-endemic regions bluetongue disease outbreaks cause significant losses and massive resources will required controlling this disease. In endemic regions, bluetongue disease pose an unceasing threat and also a financial burden to the livestock industry (MacLachlan and Osburn, 2006; Chatzopoulos et al., 2015). Cheah and Rajamanickan (1991) have shown that a possible link between the occurrences of Culicoides spp in sheep sheds and their importance to BT in Peninsular Malaysia. In areas where Cullicoides is a menace to livestock, they can be prevented by provision of protective housing for animals and this has been shown to help significantly in preventing transmission of arboviruses such as Bluetongue between animals. This method of protection against this vector has been practiced in Malaysia over the years (Cheah and Rajamanickan, 1991).
Bluetongue outbreaks have been reported among livestock in Malaysia during the early 1990s but was eventually controlled (Hassan et al., 1996). Since then few studies have paid attention to the status of Bluetongue in Malaysia. Notable studies where carried by Sharifah et al. (1995) who showed multiple BTV serotypes circulating in Malaysian cattle and sheep. About a decade later, BTV were isolated from sentinel cattle in Peninsular Malaysia and in Indonesia (Pritchard et al.,2004). To the best of the authors’ knowledge, the only serological study carried out for BT in ruminants was in the late 1970s (Anon, 1978) where antibodies to BTV were detected using AGID. This study however did not provide a definite seroprevalence rate. The objective of this study is to determine the seroprevalence of bluetongue among goats in selected small ruminant farms in Selangor, Malaysia.
Materials and Methods
All experimental procedures were performed according to the guidelines for the care and use of animals as approved by Institutional Animal Care and Use Committee of Universiti Putra Malaysia, Animal Welfare Act (2014). All applicable institutional guidelines for the care and use of animals were followed.
Animals and Sample Collection
A total of 100 adult goats of both sexes were enrolled in this study from five small ruminant farms in Selangor, Malaysia. Blood samples were collected via jugular venopuncture using plain vacutainer tubes for serology analyses. Blood samples were centrifuged at 3000 rpm for 5 minutes, after which the harvested serum was transferred into a 1.5 mL micro centrifuge tube (Eppendorf). Sera were then stored at -20°C until analysis.
Sera were tested for antibodies to Bluetongue virus using a competitive Enzme-Linked-Immunosorbent-Assay (Bluetongue Virus Antibody Test Kit, cELISA, VMRD, Inc., USA). The test was performed according to the instruction of the manufacturer. Both positive and negative control sera were included in the Assay. The results were read using an absorbance spectrophotometer where the optical densities of all the samples were measured at 630nm.
The optical density of the negative control was found to be between 0.3000 to 2.000 while that of the positive control was ½ of the means of the negative control. Optical densities with values of < ½ of the negative controls where considered positive while those with > ½ of the negative controls were considered negative. The result obtained in this study showed that out of the 100 serum samples tested for the presence of antibodies to bluetongue virus, none was positive.
Bluetongue was hitherto being an endemic disease in Malaysian livestock during the 1990s (Saharee and Fatimah, 1993; Hassan et al., 1996; Mintiens et al., 2008). The disease was however controlled and ever since, there had been very few information regarding the presence of bluetongue disease in Malaysia. This study presents the current prevalence rate of BTV antibodies among goats from different farms in Serdang, Malaysia and it shows that goats sampled in this study do not have antibodies against BTV as evidenced by the serological result. This sero-negativity could be due to standard preventive measures instituted against infectious agents. Livestock owners from the selected farms have shown strict compliance to preventive measures set by the Department of Veterinary Services of Malaysia based on the guidelines prepared by OIE for Bluetongue disease. There could also be a possibility of resistance to bluetongue virus infection in local livestock as demonstrated during the outbreak that occurred in the late 1980s. This could be associated to the production of antibodies directed against BTV by livestock in the area during that time (Hassan et al., 1996). A study carried out a decade ago still confirms the persistence of BTV in south east Asia with the isolation of BTV from sentinel cattle in Malaysia and in two locations in Indonesia (Pritchard et al., 2004).
The prevalence rate reported in this study is quite different from other studies on seroprevalence of bluetongue virus antibodies in goats in other parts of the world. Although, there is a variation in seroprevalence rates worldwide, there is no report that shows a seronegative livestock. High seroprevalence rates (67.7-84.57%) have been reported in livestock population in Iran, Grenada and Sudan (Elhassan et al., 2013; Mozafari et al., 2014; Sharma et al., 2016). Moderate seroprevalence rates (27-53.3%) have also been reported in Algeria and Saudi Arabia respectively (Hafsa et al., 2011; Yousef et al., 2012). Furthermore, low seroprevalence rates (5.3%) to BTVantibodies have equally been reported in Kerala, India (Ravishankar et al., 2005).
The distribution of BTV among livestock as reported from different countries in the tropics and sub tropics is dependent upon the presence of its vector (the Culicoides midge), climate, geography, host susceptibility and altitude as they all affect the occurrence and activity of the vectors (Braverman and Cheichik, 1996; Purse et al., 2005; Mozaffari et al., 2014). Climatic conditions are major risk factors to the occurrence of the vector for BTV since Culicoides requires warmth and moisture for both breeding and feeding (Mozaffari et al., 2014). In regions where Culicoides exists, the vector does so in areas with high environmental temperatures (St. George, 1995). Climatic conditions in this study area are characterized by high humidity and frequent rains which is ideal for Culicoides propagation. However, this vector was not found in the sampling area which may explain the seronegativity observed in this study.
It was concluded that the goats sampled in this study were either not exposed to bluetongue virus or they could have been resistant to bluetongue virus infection. Further studies using a bigger sample size, multiple species and a larger study area will be required to elucidate on the epidemiology of bluetongue virus in livestock of Malaysia.
The authors have none to declare.
FFAJ, IDP and YA conceived the idea on this research. IDP, YA, AIAM, AAB, IUH, participated in sample collection and analysis. IDP, FFAJ, YA wrote the first draft of this manuscript. All authors adopted the final manuscript.