Evidence of Pseudorabies Virus Shedding in Feral Swine (Sus Scrofa) Populations of Florida, Usa

Abstract

: Feral swine ( Sus scrofa) are a pathogen reservoir for pseudorabies virus (PrV). The virus can be fatal to wildlife and contributes to economic losses in the swine industry worldwide. National surveillance efforts in the US use serology to detect PrV-specific antibodies in feral swine populations, but PrV exposure is not a direct indicator of pathogen transmission among conspecifics or to non-suid wildlife species. We measured antibody production and the presence of PrV DNA in four tissue types from feral swine populations of Florida, US. We sampled blood, nasal, oral, and genital swabs from 551 individuals at 39 sites during 2014-16. Of the animals tested for antibody production, 224 of 436 (51%) feral swine were antibody positive while 38 of 549 feral swine (7%) tested for viral shedding were quantitative polymerase chain reaction (qPCR)-positive for PrV. The detection of PrV DNA across all the collected sample types (blood, nasal, oral, and genital [vaginal] swabs) suggested viral shedding via direct (oronasal or venereal), and potentially indirect (through carcass consumption), routes of transmission among infected and susceptible animals. Fourteen of 212 seronegative feral swine were qPCR-positive, indicating 7% false negatives in the serologic assay. Our findings suggest that serology may underestimate the actual infection risk posed by feral swine to other species and that feral swine populations in Florida are capable of shedding the virus through multiple routes.

Detection of Pseudorabies Virus in Wild Boar Foetus

“…Considering the virological analysis, only one out of 24 pregnant sows shed the virus, as indicated by the PCR positive result on the nasal-genital swab. This data is in accordance with other studies that identified percentages of shedding individuals ranging from 1% to 6% inside of a population with high seroprevalence rates (50%-60%) [7,9]. Interestingly, pooled foetuses collected from the pregnant sows also resulted in positive to virological analysis, indicating the ability of PRV to infect the foetuses during pregnancy in a viraemic status.…”

“…This appears to be in contrast with the previous literature, in which higher seroprevalence rates are generally reported in females. In fact, sows live in "maternal groups" [3,9,39] and therefore have a greater possibility of oronasal transmission of the virus between individuals, compared to males who are solitary and meet their conspecifics only during the mating season.…”

“…Higher viral seroprevalence in females, along with the presence of viral DNA in nasal secretions, suggests that PRV is mainly transmitted oro-nasally within female groups throughout the year, whereas venereal transmission is limited to the mating season [3,6,7]. Secondary routes of transmission are through contact with fomites or by ingestion of contaminated carcasses of other infected animals, such as feral swine, wild boar, rodents, or carnivores [2,8,9].…”

Pseudorabies detected in hunting dogs in Alabama and Arkansas after close contact with feral swine (Sus scrofa)

“…Since feral swine home ranges are typically influenced by food availability and unrestricted compared to livestock, movement to a neighboring county would not be unexpected [ 23 ]. Though serological results are not equivalent to shedding rates, evidence of viral shedding has been detected in multiple tissue types suggesting various routes of transmission [ 24 ].…”

Loci Associated With Antibody Response in Feral Swine (Sus scrofa) Infected With Brucella suis

“…In the United States (U.S.) there are ∼6 million invasive feral swine (Sus scrofa), which are defined as any released or escaped domestic pigs, Eurasian wild boars, or hybrids of the two (1,2). Both the abundance of feral swine and extent of the geographic range have increased rapidly over the past 30 years due to the high reproductive potential of the species, limited predation pressure, abundance of food (both native flora and fauna and agricultural products), and human-mediated introduction into uninvaded habitats (3,4). As range and abundance have increased, so too have the economic and ecological costs of feral swine.…”