Porcine Parvovirus - Treatment and Prevention

Treatment and Prevention

There is no treatment for PPV-induced reproductive failure.

Gilts should be either naturally infected with PPV or vaccinated for PPV before they are bred. To promote natural infection, a common practice is to arrange contact between seronegative gilts and seropositive sows, with the expectation that one or more of the sows will be shedding virus. Moving gilts to a potentially contaminated area, either currently or recently inhabited by seropositive swine, also can be recommended. Once infection is started, the virus spreads rapidly among fully susceptible swine. Just how effective these procedures are in increasing the incidence of natural infection is unknown. For whatever reasons, infection is common, and probably well over one-half of all gilts in areas where PPV is enzootic are infected before they are bred for the first time.

The use of vaccine is the only way to ensure that gilts develop active immunity before conception. Both inactivated and modified live-virus (MLV) vaccines have been developed. An inactivated vaccine has been tested under field conditions, and both types of vaccines were effective when tested under controlled laboratory conditions.

Vaccines should be administered several weeks before conception to provide immunity throughout the susceptible period of gestation but after the disappearance of passively acquired colostral antibody, which could interfere with the development of active immunity. These limits may define a very brief interval for effective vaccination of gilts that are bred before 7 months of age. Although inactivated vaccine provides maximum safety, there is experimental evidence that PPV can be sufficiently attenuated so that it is unlikely to cause reproductive failure even if inadvertently administered during gestation. The apparent safety of MLV vaccine may be due to its reduced ability to replicate in tissues of the intact host and cause the level of viremia needed for transplacental infection. Moreover, it has been shown by transuterine inoculation of both virulent and attenuated virus that a much larger dose of attenuated virus is required to establish infection of fetuses. Duration of immunity following vaccination is unknown; however, in one study antibody titers were maintained for at least 4 months after administration of an inactivated vaccine. Low levels of antibody found to be protective allow speculation that, once the immune system has been primed with PPV, subsequent exposure to virulent virus during gestation is unlikely to result in transplacental infection even if antibody from vaccination is no longer detected.

Vaccination is recommended also for seronegative sows and boars. Seronegative sows are usually found only in PPV-free herds; in such cases, inactivated vaccine is indicated. Experience has shown that few herds can be expected to remain free of PPV even if access is carefully controlled. Introduction of PPV into a totally susceptible herd can be disastrous. Vaccination of boars should reduce their involvement in dissemination of the virus.

Vaccines are used extensively in the United States and in several other countries where PPV has been recognized as an economically important cause of reproductive failure. All federally licensed vaccines marketed in the United States are inactivated.