ETIOLOGY, PATHOGENESIS AND DIAGNOSIS
Parvovirus is a very frequent and important cause of infertility in first-ever sows throughout the world. This pathology is caused by a single-stranded DNA virus without wrapping, so it is very resistant to environmental conditions, for several months, and most disinfectants.
This virus replicates in the intestine, without causing clinical signs in fattening or rearing pigs. Infected replacement sows are immunized, but when the infection appears during the first gestation and they are not previously immunized, the virus causes different problems depending on the stage of fetal development. These reproductive problems are frequent during the first and second gestations, but later the sows have lifelong immunity and the following deliveries will be normal.
The route of transmission is by aerosol or also of less frequent form sexual way and the period of incubation usually is of about 10 days. In pregnant sows, the virus passes through one end of the uterine horn producing fetal death continuously, and this passage from one fetus to another occurs approximately every 4 days.
If the infection occurs before day 35 the fetuses are reabsorbed, therefore, a high percentage of repetitions will be observed. When the infection occurs between 35 and 70 days of gestation the fetuses will be mummified in different sizes, since in this case they will have the skeleton formed. But after 70 days the fetuses are immunocompetent and are born normally. Maternal immunity lasts approximately 4 - 6 months in animals born from infected bristles.
Therefore, with this infection different problems happen as:
- Cyclic and acyclic repetitions according to the time of infection by embryo resorption
- Few live piglets
- Expulsion of mummified fetuses
- Occasional infertility
• Clinical diagnosis is made by observing reproductive problems, such as repetitions, the presence of small litters and mummified animals of different sizes and the absence of abortions. So, if born dead from day 70 would not be caused by Parvovirus. Differential diagnosis should always be compared with PRRS, since mummification is also observed. Other pathologies where mummified piglets appear are Classical Swine Fever and Aujeszky.
• Laboratory diagnosis consists of viral detection or serology:
- Virus detection: It is better to detect the presence of the virus in the dead or mummified fetuses, because the sows can give positive by the vaccination or to suffer the infection before the gestation. Detection of the virus can be done primarily by ELISA capture of fetal macerates, PCR or immunohistochemistry.
- Serology (ELISA, inhibition of haemagglutination): Serological analysis should be done on live piglets before giving colostrum or on sows to see seroconversion.