Pogranichniy R, Lee K, Machaty Z. Detection of porcine parvovirus in the follicular fluid of abattoir pigs. J Swine Health Prod. 2008;16(5):244–246

Cite as: Pogranichniy R, Lee K, Machaty Z. Detection of porcine parvovirus in the follicular fluid of abattoir pigs. J Swine Health Prod. 2008;16(5):244–246.
Also available as a PDF.

Keywords: swine, porcine parvovirus, follicular fluid, polymerase chain reaction
Search the AASV web site for pages with similar keywords.

Received: September 9, 2007
Accepted: April 24, 2008

Although it is generally accepted that the use of embryo transfer is safer for the distribution of germ plasm than the movement of live animals, the relative risk of transmitting infectious agents via embryo transfer is not negligible.¹ The epidemiological hazard related to the technology depends on the donor species, the method of embryo production applied, and the specific pathogens involved. In cattle, washing the embryo with or without trypsin after collection is a simple procedure to generate specific-pathogen-free embryos.² However, in pigs and small ruminants, the association between embryos and pathogens tends to be stronger.³ When pig embryos were artificially exposed to seven different pathogens, some embryos were always positive for each pathogen even after extended washing.⁴ Although this does not necessarily cause infection in the recipient animal or the offspring,^5,6 the tight embryo-pathogen association in the pig remains a concern.^7,8

Porcine parvovirus (PPV), a ubiquitous virus that affects swine reproductive performance all over the world, has been identified as a major cause of embryonic and fetal death in pigs.^9-11 Porcine parvovirus infections are generally considered harmless to adult animals because the antibodies produced against the pathogen efficiently neutralize the virus. However, when embryos are infected before their immunological competency is activated (ie, prior to 70 days of gestation), embryonic and fetal death may occur.¹²

According to a recent report, approximately 30,000 swine embryos were transferred in 2005 worldwide.¹³ This annual number is likely to increase, and the commercial application of the technology clearly carries a level of biohazard that must be diminished or eliminated with implementation of appropriate biosecurity measures. Material obtained from commercial slaughterhouses is often used to produce embryos in vitro. Since many reproductive problems caused by viral infection exist in livestock species in the field, the epidemiologic potential of current and emerging technologies must be monitored continuously.¹ The objective of the present study was to determine the presence of viral pathogens in follicular fluid samples collected from abattoir-obtained porcine ovaries. We report the presence of PPV in a number of ovarian samples, which identifies a potential hazard affecting the safety of embryo transfer technologies in the pig.

Materials and methods

Ovaries from 49 prepubertal gilts were collected at a slaughterhouse and transported to the laboratory in warm (35°C) physiological saline. The animals were selected from different farms prior to slaughter, over a period of 4 weeks. Chemicals were purchased from Sigma-Aldrich Chemical Company (St Louis, Missouri), unless otherwise indicated. The follicular fluid and oocyte-cumulus complexes were removed from the individual ovaries using a disposable syringe and a 20-gauge hypodermic needle, transferred to separate microcentrifuge tubes, and frozen immediately at -80°C. They were subsequently thawed and tested in duplicate by polymerase chain reaction (PCR) for porcine parvovirus (PPV), porcine circovirus types 1 and 2 (PCV1 and PCV2, respectively), porcine reproductive and respiratory syndrome virus (PRRSV), and pestiviruses, namely, bovine viral diarrhea virus (BVDV) and border disease virus (BDV). Viral DNA or RNA was extracted from 0.15 to 0.2 mL of each sample using a commercial kit (Qiagen Inc, Valencia, California) according to the instructions of the manufacturer. Two μL of each nucleic acid extract was used for amplification under previously described PCR conditions.^14-18 The target sequence for each virus was visualized after agarose gel electrophoresis of the PCR products, using 100-bp DNA ladders (Roche; Indianapolis, Indiana) and molecular size determination.

Results

A total of 49 samples was tested, with similar PCR results for each pair of duplicate samples. Six samples (12.2%) tested positive for PPV, with the amplified DNA fragment of the expected size clearly detectable after gel electrophoresis in each case. Nucleic acids of PRRSV, PCV1, PCV2, BVDV, and BDV were not identified in the follicular fluid of the slaughtered animals.

Discussion

In this study, porcine follicular fluid from pig ovaries collected at a slaughterhouse was monitored for a number of viral pathogens, including PPV,⁹ that can cause reproductive failure in sows and gilts. The syndrome of stillbirth, mummification, embryonic death, and infertility (SMEDI) was described several decades ago,¹⁹ and subsequent research identified the pathogen associated with the syndrome as a DNA virus belonging to the Parvoviridae family.²⁰ Later, the virus was isolated from pigs with various manifestations of reproductive failure,^21,22 and results of experiments infecting pregnant animals with the virus established that isolated PPV can infect not only the dam but also the developing fetus.^10,23 Penetration of the placental barrier is believed to occur via maternal macrophages as vehicles.²⁴ The pathological outcome depends on the time of exposure during gestation. Infection of the embryo before 35 days of gestation causes death and resorption, while fetuses infected in late gestation survive infection due to the immunocompetency acquired approximately day 70 post conception.^9,25 The virus replicates in the proliferating cells of the fetus, and reproductive failure is caused by the direct effect of PPV on a variety of vital tissues and organs, including the placenta.^26,27

An earlier study reported PPV antibody in the follicular fluid of 94.3% of sows and 78.1% of gilts examined at an abattoir.²⁸ In the present study, PPV was detected in the antral follicles of 12.2% of animals. The presence of the virus in the oocyte cytoplasm was not monitored. However, even without viral contamination of the oocyte cytoplasm, the presence of the virus on the surface of the zona pellucida poses a risk to the embryo after hatching. Several pathogens have been shown to adhere strongly to the zona of embryos produced in vitro, and mechanical washing or trypsin treatment of in vitro-derived embryos do not provide the same benefit that results from cleansing in vivo embryos.⁴ Culture conditions of in vitro embryo production provide an ideal environment for replication of viruses through adequate time, substrate, and permissive cells. This can effectively amplify the number of viruses to high levels by the end of the culture period.²⁹ Failure to cleanse viruses from in vitro embryos and amplification of viral infections during culturing may be associated with higher embryonic death rates and lower pregnancy rates after embryo transfer. Therefore, testing all abattoir material for contaminating agents is a critical control for production and transfer of in vitro embryos.¹ It remains to be determined whether the quantity of PPV that is associated with the embryos is sufficient to constitute an infectious dose for the recipients. According to one report,³⁰ PPV was able to cross the intact zona pellucida and infect embryonic cells. If this is verified, it would further emphasize the potential biohazard PPV poses during the application of embryo-associated technologies.

On the basis of our data, we conclude that PPV is a clinically significant pathogen that is present in the reproductive organs of females from a representative swine population. Other viruses known to cause abortion and embryonic losses in pigs (PCV1, PCV2, PRRSV, BVDV, and BDV) were not identified in the follicular fluid analyzed in this study. The results emphasize the importance of using pathogen-free biomaterial for embryo production, especially with the development of new and innovative reproductive technologies that present a level of risk to biosecurity.

Implications

• Porcine parvovirus is present in the follicular fluid of some gilts and sows sent to slaughter.

• When embryos produced by in vitro fertilization of abattoir-obtained oocytes are used for embryo transfer, it is advisable to perform an embryonic wash in an appropriate solution before transfer to eliminate or diminish the transmission of viral pathogens.

• Ideally, oocytes used for in vitro fertilization and subsequent embryo transfer should be collected from females free of known reproductive pathogens.

Acknowledgement

The authors would like to thank Olivia Anstaett for technical assistance during the study.

References

1. Givens MD, Gard JA, Stringfellow DA. Relative risks and approaches to biosecurity in the use of embryo technologies in livestock. Theriogenology. 2007;68:298–307.

2. Stringfellow DA. Recommendations for the sanitary handling of in vivo-derived embryos. In: Stringfellow DA, Seidel SM, eds. Manual of the International Embryo Transfer Society. Savoy, Illinois: International Embryo Transfer Society; 1998:79–84.

3. Guerin B, Nibart M, Marquant-Leguienne B, Humblot P. Sanitary risks related to embryo transfer in domestic species. Theriogenology. 1997;47:33–42.

4. Stringfellow DA, Riddell KP, Zurovac O. The potential of embryo transfer for infectious disease control in livestock. NZ Vet J. 1991;39:8–17.

5. Wrathall AE, Mengeling WL. Effect of porcine parvovirus on development of fertilized pig eggs in vitro. Br Vet J. 1979;135:249–254.

6. Wrathall AE, Mengeling WL. Effect of transferring parvovirus-infected fertilized pig eggs into seronegative gilts. Br Vet J. 1979;135:255-261.

*7. Randall AE, Pettit MJ, Plante C, Buckrell BC, Randall GCB, Henderson JM, Larochelle R, Magar R, Pollard J. Elimination of porcine reproductive and respiratory syndrome virus through embryo transfer [Abstract]. Theriogenology. 1999;51:274.

8. Singh EL, Thomas FC, Hare WC, Eaglesome MD. Embryo transfer as a means of controlling the transmission of viral infections: X. The in vivo exposure of zona pellucida-intact porcine embryos to swine vesicular disease virus. Theriogenology 1987;27:451–457.

9. Mengeling WL, Cutlip RC. Pathogenesis of in utero infection: experimental infection of five-week-old porcine fetuses with porcine parvovirus. Am J Vet Res. 1975;36:1173–1177.

10. Mengeling WL, Cutlip RC. Reproductive disease experimentally induced by exposing pregnant gilts to porcine parvovirus. Am J Vet Res. 1976;37:1393–1400.

11. Stringfellow DA, Givens MD. Epidemiologic concerns relative to in vivo and in vitro production of livestock embryos. Anim Reprod Sci. 2000;60-61:629–642.

12. Szelei J, Zadori Z, Tijssen P. Porcine parvovirus. In: Kerr JR, Cotmore SF, Bloom ME, Linden RM, Parrish CR, eds. Parvoviruses. 1^st ed. London: Hodder Arnold Publication; 2006:435–446.

*13. Tibier M. Data retrieval committee annual report. IETS Newsletter. 2006;24:12–18.

14. Molitor TW, Oraveerakul K, Zhang QQ, Choi CS, Ludemann LR. Polymerase chain reaction (PCR) amplification for the detection of porcine parvovirus. J Virol Methods. 1991;32:201–211.

15. Pogranichniy RM, Yoon KJ, Harms PA, Swenson SL, Zimmerman JJ, Sorden SD. Characterization of immune response of young pigs to porcine circovirus type 2 infection. Viral Immunol. 2000;13:143–153.

16. Christopher-Hennings J, Nelson EA, Nelson JK, Hines RJ, Swenson SL, Hill HT, Zimmerman JJ, Katz JB, Yaeger MJ, Chase CC. Detection of porcine reproductive and respiratory syndrome virus in boar semen by PCR. J Clin Microbiol. 1995;33:1730–1734.

17. Vilcek S, Herring AJ, Herring JA, Nettleton PF, Lowings JP, Paton DJ. Pestiviruses isolated from pigs, cattle and sheep can be allocated into at least three genogroups using polymerase chain reaction and restriction endonuclease analysis. Arch Virol. 1994;136:309–323.

18. Sandvik T, Paton DJ, Lowings PJ. Detection and identification of ruminant and porcine pestiviruses by nested amplification of 5’ untranslated cDNA regions. J Virol Methods. 1997;64:43–56.

19. Dunne HW, Gobble JL, Hokanson JF, Kradel DC, Bubash GR. Porcine reproductive failure associated with a newly identified “SMEDI” group of picorna viruses. Am J Vet Res. 1965;26:1284–1297.

20. Cartwright SF, Huck RA. Viruses isolated in association with herd infertility, abortions and stillbirths in pigs. Vet Rec. 1967;81:196–197.

21. Narita M, Inui S, Kawakami Y, Kitamura K, Maeda A. Histopathological changes of the brain in swine fetuses naturally infected with porcine parvovirus. Natl Inst Anim Health Q (Tokyo). 1975;15:24–28.

22. Forman AJ, Lenghaus C, Hogg GG, Hale CJ. Association of a parvovirus with an outbreak of foetal death and mummification in pigs. Aust Vet J. 1977;53:326–329.

23. Joo HS, Donaldson-Wood CR, Johnson RH. Observations on the pathogenesis of porcine parvovirus infection. Arch Virol. 1976;51:123–129.

24. Paul PS, Mengeling WL, Brown TT Jr. Replication of porcine parvovirus in peripheral blood lymphocytes, monocytes, and peritoneal macrophages. Infect Immun. 1979;25:1003–1007.

25. Mengeling WL, Lager KM, Vorwald AC. The effect of porcine parvovirus and porcine reproductive and respiratory syndrome virus on porcine reproductive performance. Anim Reprod Sci. 2000;60-61:199–210.

26. Mengeling WL, Paul PS, Brown TT. Transplacental infection and embryonic death following maternal exposure to porcine parvovirus near the time of conception. Arch Virol. 1980;65:55–62.

27. Mengeling WL. Porcine parvovirus. In: Leman AD, Straw BE, Mengeling WL, D’Allaire S, Taylor DJ, eds. Diseases of Swine. 7^th ed. Ames, Iowa: Iowa State University Press; 1992:299–311.

28. Thacker BJ, Leman AD, Hurtgen JP, Sauber TE, Joo HS. Survey of porcine parvovirus infection in swine fetuses and their dams at a Minnesota abattoir. Am J Vet Res. 1981;42:865–867.

29. Stringfellow DA, Givens MD, Waldrop JG. Biosecurity issues associated with current and emerging embryo techniques. Reprod Fertil Dev. 2004;16:93–102.

30. Bane DP, James JE, Gradil CM, Molitor TW. In vitro exposure of preimplantation porcine embryos to porcine parvovirus. Theriogenology. 1990;33:553–561.

* Non-refereed references.