[Recent studies on Aujesky's dissease in pigs and cattle (author's transl)]. / Recent onderzoek betreffende de ziekte van Aujesky in varkens en runderen.

A standardized test model for Aujeszky disease (AD) vaccines in pigs is described. The first two vaccines tested, a modified live virus (MLV) vaccine and an inactivated vaccine, failed to produce satisfactory results. The inactivated vaccine induced a short-lived, but clear-cut increase in body temperature in some of the vaccinated pigs; the MLV-vaccine was shown to spread. Complete protection against intranasal (i.n.) challenge was not achieved with either vaccine in five-month-old pigs that had been vaccinated once or even twice two to three months previously. However, the vaccinated pigs were less severely affected, and for shorter periods, than were the control animals; losses from death did not occur. In the control groups, at least thirty per cent died, the average growth of the remainder was arrested for more than three weeks. The mean period of arrested growth after challenge of pigs vaccinated once with the MLV-vaccine was slightly shorter than that following a single vaccination with the inactivated vaccine: 5.8 and 9.5 days respectively. The average virus excretion of vaccinated pigs after challenge was less and was not as protracted as in unvaccinated controls. In pigs from sows hyperimmunized with the inactivated vaccine, maternal antibodies afforded partial protection against i.n. challenge at the age of two months. However, five-month-old pigs were fully susceptible, although most of them continued to show low levels of neutralizing antibody. The average virus excretion after challenge in the two age-groups was comparable with that in control pigs. Cattle were effectively protected by vaccination with the inactivated vaccine against i.n. challenge with AD-virus. It is recommended to vaccinate "threatened" cattle twice, for instance in the autumn when they are removed from the pastures for indoor housing. The possibility that temperature reactions may occur should be taken into account.

Aspects of heat inactivation of foot-and-mouth disease virus in milk from intramammarily infected susceptible cows.

In skim milk obtained from susceptible cows after intramammary and intravenous inoculation (primary infected milk), foot-and-mouth disease (FMD) virus type O1 was slower inactivated by heat treatment than virus that had been added to pre-exposure skim milk. Residual virus infectivity in heated primary infected milk was more efficiently detected in bovine thyroid cell cultures than in secondary pig kidney (PK2) cell cultures. Untreated primary infected milk was found to inhibit both FMD-virus and vesicular stomatitis virus plaque formation in PK2 cells, suggesting the presence of interferon. The results of further tests confirmed that the interfering activity in unheated primary infected milk was indeed caused by an interferon. Interferon excretion in primary infected milk was investigated using a series of milk samples from three cows. Maximum interferon titres were found after 24 h, coinciding with or shortly after the first virus excretion peak. The results are discussed with particular reference to the use of primary infected milk in studies of the thermal inactivation of FMD-virus.

Excretion of foot-and-mouth disease virus in oesophageal-pharyngeal fluid and milk of cattle after intranasal infection.

The virus growth in the pharyngeal area and the virus excretion in milk of susceptible and vaccinated dairy cows after intranasal instillation of foot-and-mouth disease (FMD) virus type O1 were examined. Ten vaccinated cows were purchased through a market. Of these, nine had delivered their first calf. The cows were inoculated 2-9 months after having received the last dose of vaccine. All vaccinated cows resisted the intranasal challenge. The virus multiplied in the pharyngeal area but, compared with two susceptible controls, to a limited extent. No clear relation was found between virus growth and the titre of circulating neutralizing antibody at the time of challenge. Virus was first detected in milk samples of the susceptible cows when generalized FMD lesions had developed on day four; the excretion lasted for 3-4 days. Up to 19 days after inoculation untreated milk of the vaccinated cows was examined for the presence of infectious FMD virus. Samples were inoculated onto cell cultures, fed to susceptible pigs and calves and injected intramuscularly and/or intradermolingually into susceptible steers. No infectious FMD virus could be detected, either in cell cultures or in susceptible animals. The animals did not develop neutralizing antibody against FMD virus and were subsequently shown to be fully susceptible to challenge. The results are discussed with particular reference to current problems regarding the export of milk products from countries where vaccination against FMD is practised to countries free of the disease.