Jaruwan Kampa

Bovine herpesvirus type 1 (BHV-1) and bovine viral diarrhoea virus (BVDV) infections in dairy herds: self clearance and the detection of seroconversions against a new atypical pestivirus.

The epidemiology of bovine herpesvirus type 1 (BHV-1) and bovine viral diarrhoea virus (BVDV) was studied in a population of small dairy herds that had not been vaccinated. Bulk tank milk samples of 186 herds in Thailand were collected four times between 2002 and 2004. Serum samples from individual animals in 11 herds were also taken on three occasions. The prevalence of BHV-1 in the 186 herds was 61% in 2002, decreasing to 48% in 2004 and for BVDV was 91% in 2002, decreasing to 72% in 2004. A BVDV antigen-positive calf was found in one of the 11 herds, and animals in this herd and three other herds seroconverted to a recently described atypical BVDV strain (HoBi). This study showed a significantly decreasing prevalence for both BHV-1 and BVDV due to a self-clearance process. Further studies are needed to find out how the atypical BVDV strain entered the cattle population.

BVDV and BHV-1 Infections in Dairy Herds in Northern and Northeastern Thailand

AbstractBulk milk samples from 220 dairy herds were collected at 9 public milk collection centres in the northeastern and northern Thailand, and a subset of 11 herds was selected for individual testing. The samples were tested for presence of antibodies to BVDV and BHV-1 using an indirect ELISA. The results from the bulk milk testing demonstrated a moderate level of exposure to BVDV and BHV-1 (73% and 67%, respectively). However, the low proportion of herds with high BVDV antibody-levels (13%) and the low within-herd seroprevalence of BVDV and BHV-1 in the 11 herds (24% and 5%, respectively), particularly among the young stock (15% and 0%, respectively), demonstrated a low prevalence of active BVDV infection and a low rate of reactivation of latent BHV-1. The presence of a self-clearance process was also indicated by the results from the individual testing. Moreover, a surprisingly low prevalence of BVDV and BHV-1 antibody-positive herds at one of the milk centres was found. This centre was established 5–10 years before the others. Our impression is that this reflects the self-clearance process, where consecutive replacement of imported infected animals without further spread has resulted in a nearly total elimination of the infections.Based on our experiences and on these results we are convinced that this process can continue if there is awareness of herd biosecurity. This is especially important in the context of a future intensification of the dairy production.SammanfattninBVDV och BHV-1 infektioner i mjölkkobesättningar inorra och nordöstra Thailand. Tankmjölksprover insamlades från 220 mjölkkobesättningar belägna i 2 regioner i norra respektive nordöstra Thailand. Insamlingen gjordes vid 9 regionala mjölkinsamlingscentra. Ett urval bestående av 11 besättningar gjordes för individuell provtagning. Samtliga prover analyserades medelst indirekt ELISA avseende förekomst av antikroppar mot BVDV och BHV-1. Resultaten visade en måttlig exponeringsgrad av såväl BVDV som BHV-1 (73% respektive 67%). Den låga förekomsten av besättningar med höga nivåer BVDV-antikroppar i tankmjölk (13%) och den låga individuella BVDV- respektive BHV-1-seroprevalensen bland ungdjur talar dock för en låg grad av reaktivering av latent BHV-1 och en låg prevalens av aktiv BVDV-infektion. Resultaten från den individuella provtagningen indikerar en progressiv självsanerande process i 9 av de 11 besättningarna. Vi fann dessutom en förvånansvärt låg prevalens av såväl BVDV som BHV-1 bland de besättningar som tillhörde uppsamlingsområdet för ett av de nio mjölkinsamlingscentra. Dessa besättningar etablerades 5–10 år tidigare än majoriteten av de övriga besättningarna. Vi tror att den nyrekrytering som skett under årens lopp i dessa besättningar inneburit att importerade infekterade djur ersatts, och att detta resulterat i en nästintill total självsanering av BVDV och BHV-1. Sammanfattningsvis konstaterade vi att den regionala situationen avseende BVDV och BHV-1 var god. Vi fann indikationer på en självsanerande process i besättningarna och vi är övertygade om att denna kommer att fortsätta så länge som man är medveten om vikten av en god biosäkerhet. Detta kommer att bli särskilt viktigt vid en framtida intensifiering av mjölkproduktionen i regionen.

Evaluation of a commercial Erns-capture ELISA for detection of BVDV in routine diagnostic cattle serum samples.

BackgroundBovine viral diarrhoea virus (BVDV) is an important pathogen in cattle. The ability of the virus to cross the placenta during early pregnancy can result in the birth of persistently infected (PI) calves. These calves shed the virus during their entire lifespan and are the key transmitters of infection. Consequently, identification (and subsequent removal) of PI animals is necessary to rapidly clear infected herds from the virus. The objective of this study was to evaluate the suitability of a commercial Erns-capture ELISA, in comparison to the indirect immunoperoxidase test (IPX), for routine diagnostic detection of BVDV within a control programme. In addition, the effect of passive immunity and heat-inactivation of the samples on the performance of the ELISA was studied.MethodsIn the process of virus clearance within the Swedish BVDV control programme, all calves born in infected herds are tested for virus and antibodies. From such samples, sent in for routine diagnostics to SVA, we selected 220 sera collected from 32 beef herds and 29 dairy herds. All sera were tested for BVDV antigen using the Erns ELISA, and the results were compared to the results from the IPX used within the routine diagnostics.ResultsAll 130 samples categorized as virus negative by IPX were tested negative in the ELISA, and all 90 samples categorized as virus positive were tested positive, i.e. the relative sensitivity and specificity of the ELISA was 100% in relation to IPX, and the agreement between the tests was perfect.ConclusionWe can conclude that the Erns ELISA is a valid alternative that has several advantages compared to IPX. Our results clearly demonstrate that it performs well under Swedish conditions, and that its performance is comparable with the IPX test. It is highly sensitive and specific, can be used for testing of heat-inactivated samples, precolostral testing, and probably to detect PI animals at an earlier age than the IPX.