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At the end of August and the first two weeks of September 2011 dozens of veterinary practitioners reported to GD Veekijker (Animal Health Service) several dairy herds with cows with sudden decreased milk production, watery diarrhea and sometimes fever. In the beginning these reports came from the Eastern region of the Netherlands, after that also from the other three regions. The percentages of diseased herds per veterinary practice varied from a few till dozens per cent. Extensive bacteriological, virological and parasitological testing of the feces of sick cows did not reveal an infectious cause of the clinical problems. Recently, 50 stored blood samples of clinically diseased cattle were tested for the Schmallenbergvirus using a PCR, and 36% (18/50) tested positive. A large group of control cows (n=115) was also tested with the PCR and all cattle tested negative. Likely the Schmallenbergvirus was the primary cause of the clinical symptoms in the Dutch dairy herds. Further research will be done to confirm this.

In a closed dairy herd in the province of Utrecht in 1995, nine replacement heifers were erroneously intramuscularly vaccinated with Tracherine, a live virus IBR vaccine. More than 18 months later, serology of the herd revealed that a large part of the herd had developed an antibody response towards BHV1 (62 of 87 animals). To investigate whether Tracherine had recirculated on the farm, four BHV1 antibody positive animals, of which two had been vaccinated with Tracherine, were treated with corticosteroids to reactivate latent BHV1. Two virus isolates were obtained and subsequently analysed by resctriction enzyme analysis. Both isolates were identified as BHV1.1 subtypes. One of the isolates was clearly distinct from Tracherine and was most likely a BHV1 field virus. A BHV1 field virus was most likely introduced into the farm even though the herd was closed, the animals had not been in contact with other cattle, and preventive hygienic measures had been implemented. There was no indication that Tracherine had recirculated.

This article discusses risk analysis of infectious diseases in a cattle population. Heck cattle living in nature reserve 'De Oostvaardersplassen' were studied as an example of the risk analysis approach. Twenty-five adult cattle were tested for every infectious disease agent that the risk analysis indicated might be prevalent. All sampled cattle tested positive for Bovine Herpesvirus 1, whereas the prevalence of antibodies against other infectious disease agents was below the level that was assumed to be the threshold for spread of the disease to cattle in the surrounding areas. Risk management of infectious diseases was expressed in a so-called 'low-risk profile'. The risk of introduction or spread of infectious diseases was estimated to be very low as long as the population was kept strictly enclosed.

Viral zoonotic diseases can be defined as 'Viral diseases transmitted from vertebrate animals to man'. Viral zoonoses have been emerging and re-emerging throughout history and can cause serious diseases and disease outbreaks in human populations. This paper deals with emerging viral zoonotic infections that have hosts in native species and can be a hazard for the human population in the Netherlands. Rabies virus, hantavirus, influenza virus tick-borne encephalitis virus, borna disease virus and prions will be discussed.

Cattle are vaccinated with a live gE-negative BHV1-marker vaccine as a part of a programme to eradicate bovine herpes virus 1 in the Netherlands. To investigate whether this vaccine is transmitted to unvaccinated cattle in a herd after intramuscular administration, cattle from two herds were vaccinated: of a herd of 114 BHV1-antibody negative cattle on one farm, 45 animals were vaccinated, and of a dairy herd of 55 cattle in another farm, all 10 BHV1-positive animals were vaccinated. Vaccination was repeated after about a month. Antibodies against BHV1 were determined in all unvaccinated cattle to detect potential BHV1-antibody responses. Only one unvaccinated cow (from the dairy herd) showed BHV1 seroconversion. However, this antibody response was detected by a gE-ELISA as well as by a gB-ELISA. This indicates that the animal was infected by a field virus and not by the gE-negative vaccine virus. Thus intramuscularly administered live gE-negative BHV1 marker vaccine did not spread to unvaccinated cattle (n =154) on two farms.