Special Topic on Swine Diseases - Porcine Parvovirus

Pathogen: Porcine parvovirus (PPV) belongs to the Parvoviridae family and the Parvovirus genus. The virus particles are round or hexagonal in shape, non-enveloped, approximately 20 nm in diameter, and contain single-stranded DNA. The virus is highly resistant to heat, remaining stable at 40°C, and is resistant to both acidic and alkaline conditions, remaining stable at pH 3.0–9.0. It can resist lipid solvents such as ether and chloroform, but can be inactivated by 0.5% bleach or 1%–1.5% sodium hydroxide within 5 minutes.

Epidemiology: PPV is widely distributed among pig populations worldwide, with pigs of all ages, sexes, and breeds susceptible to infection. It can occur as localized or sporadic outbreaks, and particularly in naïve pig populations, it can lead to acute outbreaks, causing significant reproductive problems such as abortions and stillbirths in first-time sows. The primary sources of infection are infected boars and sows. Infected sows can transmit the virus to their fetuses via the placenta. The virus can also be found in dead fetuses, mummified fetuses, live piglets, and uterine secretions. Infected boars play an important role in the transmission of PPV. During the acute infectious period, the virus can be excreted through various routes, including semen. Contaminated pig pens are also an important source of PPV transmission.

Symptoms: Pregnant sows may experience reproductive disorders such as abortion, stillbirth, mummified fetuses, and infertility after prolonged periods without successful mating. Other pigs infected with the virus may not show obvious clinical symptoms. Outbreaks of the disease in pig herds are often associated with clinical signs like an increased number of mummified fetuses, reduced litter size, difficult deliveries, and repeated mating attempts. If infection occurs during the early pregnancy (30–50 days), embryos may die or be resorbed, causing infertility and irregular estrous cycles. If infection occurs in mid-pregnancy (50–60 days), fetal death results in mummified fetuses. In late pregnancy (60–70 days and beyond), fetuses with immune capabilities may survive and develop lifelong virus carriers, though they can remain infected. The only visible sign in sows is the death of fetuses in mid or late pregnancy, with the absorbed fetal fluids reducing the sow's abdominal size.