Pigs are either directly or indirectly the source of infection with Herpes virus suis in dogs and cats. On oral or oronasal infection, the virus is spread by way of the cranial nerves to the central nervous system. The incubation period is short: from one to six days. The disease is mainly characterised by nervous disorders. Pruritus is a characteristic clinical sign but is not present in every case. Mortality in dogs and cats is a hundred per cent. In rural areas, infection is caused by consumption of uncooked pork or offal from pigs. Prevention is possible by avoiding exposure to pigs or fresh pig products. It is possible to vaccinate dogs and cats with an inactivated vaccine. Results of vaccination studies show some variation, however.