Etiology, Pathogenesis and Diagnosis in swine parvovirosis

Swine parvovirus (PPV) is a very common and important cause of infertility in first parity sows worldwide. This disease is caused by an unwrapped simple-chain DNA virus, very resistant to weather conditions and to most disinfectants.

This virus replicates in the gut, without causing clinical symptoms in fattening or breeding pigs. Infected replacement sows are immunized, but when the infection appears during the first gestation and is not previously immunized, the virus causes different problems depending on the fetal development state. These reproductive problems are common during the first and second gestation, then, sows acquire lifetime immunity and following farrowings will be normal.

The transmission pathway is by aerosol or, less frequently, sexually, and the incubation period is usually 10 days. In pregnant sows, the virus goes through the end of one of the uterine horns, causing fetal death, and is transferred from one fetus to another every 4 days.

If the infection occurs before the 35^th day of gestation, the fetuses are reabsorbed, so a high percentage of repetitions are observed. When the infection takes place between 35 and 70 days of pregnancy, the fetuses are mummified in different sizes, because, in this case, their skeleton is already formed. After 70 days of pregnancy, fetuses are immunocompetent and born normally. Maternal immunity lasts for approximately 4-6 months in animals born from infected sows.

Therefore, different problems are caused by this disease such as:

• Cyclical and non-cyclical repetitions (embryonic reabsorption), depending on the moment the infection takes place
• Decreasing number of live piglets
• Expulsion of mummified fetuses
• Occasionally, infertility

Clinical diagnosis is made by the observation of reproductive problems, such as repetitions, the presence of small litters, mummified animals of different sizes and the absence of abortions. Therefore, in a parvovirus infection we won’t observe dead piglets that are over their 70th day of gestation. For differential diagnosis, keep in mind Porcine Reproductive and Respiratory Syndrome (PRRS), because it also causes mummifications. Other pathologies that cause mummification of piglets are Classic Swine Fever and Aujeszky’s disease.

Laboratory diagnosis consists of viral detection or serology:

• Viral detection: The best way to detect the presence of the virus is in the dead or mummified fetuses, because sows can be also positive because of vaccination or by suffering the infection before the gestation. Virus detection can be done by capture ELISA of fetal macerations, PCR or immunochemistry.

• Serology (ELISA, inhibition of hemagglutination): Serological analysis should be done from live piglets before taking colostrum or in sows to detect seroconversion.