*3.2.6. Porcine parvovirus*

The porcine parvovirus (PPV) has worldwide distribution and is responsible for reproduc‐ tive failures that are characterized by embryonic death, fetal mummification and stillbirth [73]. PPV can be a non encapsulated virus. It is resistant to adverse environmental condi‐ tions, which facilitates its dissemination. In addition, there may be venereal transmission of the virus from the infected semen. Besides the semen, the virus can be detected in testis, in the scrotal lymph nodes and in epididymis [6].

The techniques for virus detection are diverse and the direct immunofluorescence and PCR are the most commonly used methods. Serology can also confirm the presence of the anti-PPV antibodies. Although the virus isolation may be necessary to detect the viral sample, the fetal tissues are toxic to cellular cultures, therefore limiting the use of this technique in some situations [74].

The PPV-induced reproductive failures can be prevented by making sure that the develop‐ ment of the females' immune response occurred before conception. The immune response can result from natural exposure or from vaccination which is a common practice and per‐ formed at least annually [74].

the presence of the virus. Thus, the contamination via oocytes in naturally infected animals is not a natural route [78]. Yet this author and collaborators found that the virus can adhere firmly to either oocyte-cumulus complex and pellucid zone of embryos at the initial devel‐

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At embryonic level, it has been demonstrated that the replication of some viruses can occur in the embryonic cells. In this context, the Pellucid Zone (ZP) of the embryos acts as a barrier protecting the embryo against viral agents. Therefore, after disruption of the pellucid zone at stage of the hatched blastocysts, some viruses such as the classical swine fever virus and PCV-2 can replicate in embryonic cells as carrying a deleterious effect, especially in embryos produced in vitro [79, 80]. The greatest weakness of the embryos produced in vitro may be due either to a thinner pellucid zone of those embryos [81] and greater exposure to laborato‐ rial conditions and culture media that can act as contamination sources. It is known that ZP of pig embryos is much stickier than that of cattle, although the reason for this fact to be not known [82]. It is believed that lower-sized virus (20 -26 nm), such as *porcine circovirus 2* and porcine parvovirus could even surpass the ZP of embryos produced in vivo by promoting contamination of the embryonic cells [13, 80]. However, this issue is still controversial and

Thus, it is expected the contamination of the embryonic cells of the ZP-unprovided embryos will depend mainly on nature of the virus, of the embryonic development stage and the presence of viral receptors expressed in target cells [82]. Furthermore, the ZP- unprovided embryos that are produced in vitro are much more sensitive to viral contamination and, in‐ dependent of the nature, they represent a real source for contamination of the animals main‐ ly by diseases caused by virus. Finally, the disinfection of the swine embryos by using washing and treatment with enzymatic combination rather represents a reasonable alterna‐

Because the differences in the prevalence rates of the diseases among countries and even re‐ gions, the control strategies will differ according to incidence of each disease. Therefore, the policies for eradication, vaccination and isolation of the animals in farms are very dependa‐

The preventive procedures against transmission of infectious diseases via semen depend on the control routine. The AI must be understood as a contaminative potential for swine females, since it is a vehicle for disease transmission. Thus, the insemination cen‐ ters should be regularly controlled and monitored according to specific criteria. Howev‐ er, even before considering the potential for contamination through semen, it is necessary to pay attention to the possibility for disease introduction through acquisition of a living animal. Thus, some practices such as the introduction of animals which are serologically negative or animals proceeding from seronegative herds and to avoid the contact of the animals pertaining to insemination center with external people are essen‐

opment stage despite not affecting the embryonic development.

tive for programs of the in vitro embryonic production [78].

**5. Possible control procedure to be performed**

ble on the types of disease the animals would be more exposed.

further studies are still needed.
