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Is PEDv spread via semen?

Enric Marco comments on the practical implications of a recent research article about PEDv excretion in semen.

Monday 26 March 2018 (1 years 9 months 25 days ago)
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Commented article
S Gallien, A Moro, G Lediguerher, V Catinot, F Paboeuf, L Bigault, M Berri, PC Gauger, N Pozzi, E Authié, N Rose and B Grasland. Evidence of porcine epidemic diarrhea virus (PEDV) shedding in semen from infected specific pathogen-free boars. 2018. Vet Res (2018) 49:7.
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Amongst all the pig infections, the epidemiology of porcine epidemic diarrhoea (PED) has been, surely, one of the most debated. After entering the United States and Canada from China, the virus spread rapidly and followed the same pattern in other countries subsequently infected, such as Korea, Taiwan or Japan (in that order).

The rapid spread of the infection raised doubts about its mode of transmission, since other viral infections which route of infection is also faecal-oral, do not manage, at any rate, to spread so quickly. This was the reason for the onset of a large number of research studies in order to clarify and define the different transmission routes. In fact, potential ways that have been suggested include:

  • Obviously, contact with contaminated faecal material, either direct contact with infected animals or indirect contact with faecal material transported via contaminated feed.
  • Transportation means used by infected pigs or other contaminated materials
  • Also, the aerogenous route at short distances due to the presence of contaminated aerosols.

Sexual transmission (via contaminated semen) was assessed, but always under the belief that the semen could be contaminated, either from faecal material present in the prepuce or by aerosols containing the virus.

However, it is interesting to note that the article describes how to obtain infected semen even before the animals show clinical signs of the disease, excluding the possibility that semen positive results came from contamination by infected faeces present on the skin (prepuce) of the boar.

It is also interesting to note that semen contains PED virus intermittently for a fairly long period, at least up to 49 days. In view of these results, it seems clear that the use of contaminated semen doses would put the health status of negative farms at risk, even though, as of today, it has not yet been confirmed that sows inseminated with contaminated semen could get the disease. However, it should not be forgotten that the sole presence of PEDv-contaminated material in a farm free of the virus already poses a risk of infection, even though the final route of infection is not vaginal but oral.

The conclusions of the article do nothing but endorse what has been a rule in the main boar studs in order to preserve their health status: the implementation of a long enough quarantine period (minimum of about 4 weeks), which allows checking the negative status of the boars to be introduced in relation to different infections, among which PED should be included.

Summary of the commented article
S Gallien, A Moro, G Lediguerher, V Catinot, F Paboeuf, L Bigault, M Berri, PC Gauger, N Pozzi, E Authié, N Rose and B Grasland. Evidence of porcine epidemic diarrhea virus (PEDV) shedding in semen from infected specific pathogen-free boars. 2018. Vet Res (2018) 49:7.

What are they studying?
This study determines if PEDv could be detected in semen from artificially infected specific pathogen-free boars exposed to a US non-InDel strain.

How was it done?
Two groups of specific-pathogen-free boars were included in the trial. Two boars were inoculated with 5 ml of a homogenate containing 108 genomic copies/ml of a non-InDel strain. Two boars were kept as negative controls. The experiment lasted for a total of 52 days post-inoculation during which clinical signs (lethargy, external appearance, behaviour, breathing and diarrhoea) were recorded. Semen, faecal and serum samples were also tested using RT-qPCR.

What are the results?

Clinical signs (diarrhoea, off feed, vomiting) were seen in both inoculated boars and were more pronounced than expected considering the age of the experimental animals. The negative controls stayed healthy and uninfected.

PEDv was detected in the semen, albeit only intermittently. PEDV RNA was present in both fractions of semen, although larger amounts of PEDV were more consistently detected in the sperm-rich fraction which contains sperm and non-sperm cells (spermatozoa, leucocytes, immature germ cells, etc.). In these sperm-rich fractions, the maximum PEDV genomic load reached 3.40 × 104 genomic copies/ml for one boar and 1.75 × 104 genomic copies/ ml for the second one. Interestingly, viral excretion in the seminal fractions was transient. The swabs of the prepuce were negative for PEDV RNA at the time PEDV RNA was detected in semen. PEDV RNA was also detected in the gelatine plug at 18 and 42 days post-inoculation in both boars and at 49 days post-infection in one of them. In contrast, virus shedding was more consistent in faecal samples: samples were continuously positive for 16 and 19 days in the 2 boars.

What implications does this paper have?
The study has demonstrated the shedding of a non-InDel US PEDV strain in the semen (sperm-rich fraction and seminal fraction) of inoculated boars.

Boars, particularly their semen, need to be considered as a risk factor for the introduction/re-introduction of PED into the breeding herd. PEDV in semen appeared before shedding in faeces and prior to the onset of the clinical signs. Therefore, boars infected by PEDV may be detected after delivery of potentially infected semen. The fact that shedding is intermittent further complicates detection. Testing boars for PED seroconversion and the reporting of PED clinical signs, together with the absence of previous virus shedding in faeces, would be required. The risks are higher because the research demonstrated that PEDV RNA can be detected in semen even when the boars no longer shed virus in faeces and do not show any clinical signs.

Further studies are required to determine if the PEDV detected by RT-qPCR in infected semen is potentially infectious.

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