Affects: Cats, Dogs
Aujeszky's disease, usually called pseudorabies in the United States, is a viral disease in swine that is endemic in most parts of the world. It is caused by pseudorabies virus (PRV). Aujeszky's disease is considered to be the most economically important viral disease of swine in areas where classical swine fever (hog cholera) has been eradicated. Other mammals, such as cattle, sheep, goats, cats, dogs, and raccoons, are also susceptible. The disease is usually fatal in these animal species.
Research on PRV in pigs has pioneered animal disease control with genetically modified marker vaccines lacking an antigen, which allow for immunological differentiation of infected from vaccinated animals. PRV is now used in model studies of basic processes during lytic herpesvirus infection, and for unravelling molecular mechanisms of herpesvirus neurotropism.
Clinical Signs: Respiratory infection is usually asymptomatic in pigs more than two months old, but it can cause abortion, high mortality in piglets, and coughing, sneezing, fever, constipation, depression, seizures, ataxia, circling, and excess salivation in piglets and mature pigs. Newborn piglets may suffer mass mortality after infection, and in particular, the morbidity and mortality rates of piglets within one week of age can nearly reach 100%, but it is less than 10% in pigs between one and six months of age. Pregnant swine can reabsorb their litters or deliver mummified, stillborn, or weakened piglets. In cattle, symptoms include intense itching followed by neurological signs and death. In dogs, symptoms include intense itching, jaw and pharyngeal paralysis, howling, and death. Any infected secondary host generally only lives two to three days.
Genital infection appears to have been common in a great part of the 20th century in many European countries in swine herds, where boars from boar centres were used for natural service of sows or gilts. This disease manifestation has always been asymptomatic in affected pigs, and presence of the infection on a farm was detected only because of cases in cattle showing pruritus on the hindquarters.
In susceptible animals other than swine, infection is usually fatal, and the affected animals most often show intense pruritus in a skin area. Pruritus in Aujeszky's disease is considered a phantom sensation as virus has never been found at the site of pruritus.
Transmission: Aujeszky's disease is highly contagious. The infection is commonly considered to be transmitted among swine through nose-to-nose contact, because the virus is mostly present in nasal and oral areas. This notion, however, is contradicted by results from epidemiological studies, according to which the decisive spread within herds occurs by air currents over many meters. Correspondingly, the risk of airborne transmission of highly virulent virus strains from acutely infected herds to other swine herds has been found to be very high. The infection has been found transmitted over distances of many kilometers.
Otherwise, the infection is most often transmitted into herds by introduction of acutely or latently infected pigs.
Concerning transmission to cattle, see section above.
Prevention: Although no specific treatment for acute infection with PRV is available, vaccination can alleviate clinical signs in pigs of certain ages. Typically, mass vaccination of all pigs on the farm with a modified live virus vaccine is recommended. Intranasal vaccination of sows and neonatal piglets one to seven days old, followed by intramuscular (IM) vaccination of all other swine on the premises, helps reduce viral shedding and improve survival. The modified live virus replicates at the site of injection and in regional lymph nodes. Vaccine virus is shed in such low levels, mucous transmission to other animals is minimal. In gene-deleted vaccines, the thymidine kinase gene has also been deleted; thus, the virus cannot infect and replicate in neurons. Breeding herds are recommended to be vaccinated quarterly, and finisher pigs should be vaccinated after levels of maternal antibody decrease. Regular vaccination results in excellent control of the disease. Concurrent antibiotic therapy via feed and IM injection is recommended for controlling secondary bacterial pathogens.