A novel multiplex qPCR­HRM assay for the simultaneous detection of four abortive zoonotic agents in cattle, sheep, and goats.

Abortifacient pathogens induce substantial economic losses in the livestock industry worldwide, and many of these pathogens are zoonotic, impacting human health. As Brucella spp., Coxiella burnetii, Leptospira spp., and Listeria monocytogenes cause abortion, rapid differential molecular diagnostic tests are needed to facilitate early and accurate detection of abortion to establish effective control measures. However, the available molecular methods are laborious, time-consuming, or costly. Therefore, we developed and validated a novel multiplex real-time polymerase chain reaction (qPCR) method based on high-resolution melting (HRM) curve analysis to simultaneously detect and differentiate four zoonotic abortifacient agents in cattle, goats, and sheep. Our HRM assay generated four well-separated melting peaks allowing the differentiation between the four zoonotic abortifacients. Out of 216 DNA samples tested, Brucella spp. was detected in 45 samples, Coxiella burnetii in 57 samples, Leptospira spp. in 12 samples, and Listeria monocytogenes in 19 samples, co-infection with Brucella spp. and Coxiella burnetii in 41 samples, and 42 samples were negative. This assay demonstrated good analytical sensitivity, specificity, and reproducibility. This is a valuable rapid, cost-saving, and reliable diagnostic tool for detecting individual and co-infections for zoonotic abortifacient agents in ruminants.

Synanthropic and Wild Animals as Sentinels of Zoonotic Agents: A Study of Leptospira Genotypes Circulating in Northeastern Italy.

Leptospirosis is an infectious disease widely reported in veterinary practice and a worldwide zoonosis. In Northeastern Italy, different serogroups and genotypes of Leptospira have been described in ill dogs, the most commonly detected being Icterohaemorragiae (ICT) ST 17, Australis (AUS) ST 24 and ST 198, Pomona (POM) ST 117 and ST 289, and Sejroe (SEJ) ST 155. However, there is little information available on the environmental exposure to Leptospira of wild and synanthropic animals. The aim of this study was to identify the circulating genotypes in potential reservoirs to fill this gap of knowledge. Between 2015 and 2022, 681 animal carcasses collected by the Public Veterinary Service were analyzed for Leptospira with a real-time PCR-based screening test, while positive samples were genotyped by multi-locus sequence typing analysis. To carry out our study, we tested 330 hedgehogs, 105 red foxes, 108 Norway rats, 79 mice, 22 coypus, 10 bank voles, 13 grey wolves, 5 common shrews and 9 greater mouse-eared bats. Five sequence types (STs) common in dogs were also found in wild animals: ST 24, ST 198, ST 17 and ST 155 in hedgehogs, ST 17 and ST 24 in foxes, ST 17 in rats, ST 17 and ST 155 in mice, and ST 117 in a wolf. In addition, to the best of the authors' knowledge, this is the first Italian report of SEJ ST 197 in a bank vole. Furthermore, this study described a previous survey conducted in 2009 on coypus (30 animals from the province of Trento and 41 from the province of Padua), referring to a serological positivity (L. Bratislava) without any molecular detection of Leptospira. This study on Leptospira in synanthropic and wild animals highlighted the importance of increasing our epidemiological knowledge of leptospirosis and its zoonotic risks.

Feline Susceptibility to Leptospirosis and Presence of Immunosuppressive Co-Morbidities: First European Report of L. interrogans Serogroup Australis Sequence Type 24 in a Cat and Survey of Leptospira Exposure in Outdoor Cats.

Leptospirosis is one of the most widespread zoonotic diseases and can infect both humans and animals worldwide. The role of the cat as a susceptible host and potential environmental reservoir of Leptospira is still not well understood, due to the lack of obvious clinical signs associated with Leptospira spp. infection in this species. This study aims to describe the first European detection of Leptospira interrogans serogroup Australis ST 24 in a young outdoor cat with a severe comorbidity (feline panleukopenia virus). In addition, the results of a preliminary study conducted in 2014-2016 are presented (RC IZSVE 16/12), which reports an investigation of Leptospira exposure of outdoor cats in Northeast Italy by means of serological investigation and molecular evaluation of urine. The animals included in the survey are part of samples collected during active and passive surveillance (diagnostic samples). The study reported a seroprevalence of 10.5% among outdoor cats and the serogroups identified were Grippotyphosa, Icterohaemorrhagiae, Bratislava, Canicola and Ballum. Symptomatic cats reported high MAT titres (ranging from 1:800 to 1:1600) towards antigens belonging to the serovars Grippotyphosa (1:800), Bratislava (1:1600), Icterohaemorrhagiae (1:200) and Copenhageni (1:200-1:800). In one subject, urine tested positive for Leptospira PCR. Cats with high antibody titres for Leptospira and/or positivity on molecular test suffered from immunosuppressive comorbidities (feline immunodeficiency virus and feline leukaemia virus; feline herpesvirus and lymphoma; hyperthyroidism). The overall prevalence of serum antibodies against Leptospira found in free-ranging cats (10.53%, 95% CI: 4.35-16.70%) and the identification of L. interrogans ST 24 in a young cat with immunosuppressive disease (feline panleukopenia virus) suggest the possibility of natural resistance to clinical leptospirosis in healthy cats. In a One Health perspective, further studies are needed to better define the pathogenesis of leptospirosis in cats and their epidemiological role as environmental sentinels or possible carriers of pathogenic Leptospira.

Outbreak of Leptospira borgpetersenii Serogroup Sejroe Infection in Kennel: The Role of Dogs as Sentinel in Specific Environments.

Kennels may represent high-risk environments for the diffusion of Leptospira infection in dogs and consequently a threat to public health. This study describes an outbreak of Leptospira infection in a kennel in Italy in 2020, both with clinically ill and asymptomatic dogs. Fifty-nine dogs, including three ill dogs, were tested for Leptospira spp. infection by the microscopic agglutination test (MAT) and real-time qPCR. Multi-locus sequence typing (MLST) analysis was used to genotype the identified leptospires. Thirty of the fifty-nine (50.9%) dogs had MAT titer and/or molecular positivity indicative of Leptospira infection. Twenty-two of the fifty-nine (37.3%) dogs exhibited seropositivity against at least one serovar belonging to the Sejroe serogroup, and MLST analysis identified L. borgpetersenii serogroup Sejroe (Leptospira ST155) as responsible for the outbreak. Up to now, Sejroe serogroup infection was sporadically reported in dogs. The extension of the MAT antigen panel to several serovars belonging to the serogroup Sejroe could be useful in the diagnosis of canine leptospirosis. Dogs may serve as sentinel of leptospires in specific environments, and surveillance of Leptospira infection in kennels is strongly recommended even when the correct vaccine prophylaxis is administered, because the vaccines currently available are not able to protect from all of the serogroups.

Detection of a Novel Chlamydia Species in Invasive Turtles.

Trachemys scripta is a turtle species native to Central America. Since the 1950s, pond sliders have been imported worldwide as companion animals, but have often ended up in foreign ecosystems with great ecological consequences. Moreover, both autochthonous and invasive species of turtles can be carriers of pathogens, including Chlamydiaceae. In the present study, pulmonary tissues collected from four Trachemys scripta were tested with a 23S-targeting real-time PCR (rPCR) specific for the Chlamydiaceae family. The turtles were hosted in a rescue center for wild exotic animals located in northeastern Italy, and were found dead after the hibernation period. Two out of four individuals resulted positive in rPCR for the presence of Chlamydiaceae. Further characterization of this positivity was performed by phylogenetic analysis of the 16S rRNA and outer membrane protein A genes. The phylogenetic tree showed that these chlamydial strains are identical to a novel Chlamydia reported in 2017 in Polish freshwater turtles, and closely related to Chlamydia pneumoniae and to other chlamydial strains found in reptiles. This first finding evidences the presence of this Chlamydia strain in Italian turtles, but further studies will be necessary to confirm the presence and the strain pathogenicity and to evaluate its prevalence in the local turtles' population.

One-Year Surveillance of SARS-CoV-2 Exposure in Stray Cats and Kennel Dogs from Northeastern Italy.

Dogs and cats are susceptible to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). During the pandemic, several studies have been performed on owned cats and dogs, whereas limited data are available on the exposure to stray animals. The objective of this study was to investigate the exposure to SARS-CoV-2 of feral cats and kennel dogs in northeastern Italy, through serological and molecular methods. From May 2021 to September 2022, public health veterinary services collected serum, oropharyngeal, and rectal swab samples from 257 free-roaming dogs newly introduced to shelters, and from 389 feral cats examined during the routinely trap-neutered-return programs. The swabs were analyzed for viral RNA through a real-time reverse transcriptase PCR (rRT-PCR), and sera were tested for the presence of the specific antibody against SARS-CoV-2 (enzyme-linked immunosorbent assay). Serology was positive in nine dogs (9/257) and three cats (3/389), while two asymptomatic cats tested positive to rRT-PCR. One cat turned out to be positive both for serology and molecular analysis. In addition, this study described the case of a possible human-to-animal SARS-CoV-2 transmission in a cat that travelled in close contact to a COVID-19-positive refugee from Ukraine. This study shows that SARS-CoV-2 can infect, in natural conditions, stray cats and kennel dogs in northeastern Italy, although with a low prevalence.

SARS-Cov-2 Natural Infection in a Symptomatic Cat: Diagnostic, Clinical and Medical Management in a One Health Vision.

Despite the reported increase in SARS-CoV-2-infected pets, the description of the clinical features from natural infection and the medical follow up in symptomatic pets is still not sufficiently documented. This study reports the case of an indoor cat that displayed respiratory signs and a gastrointestinal syndrome, following the COVID-19 diagnosis of his owners. Thoracic radiographies were suggestive of bronchial pneumonia, while blood tests were indicative of a mild inflammatory process. Nasal and oropharyngeal swabs tested positive through RT-qPCR assays targeting SARS-CoV-2 genes 14 days after his owners tested positive for the virus. Nasal swabs persisted to be RT-qPCR positive after 31 days. Serology confirmed the presence of antibodies through ELISA, electrochemiluminescence analysis and plaque reduction neutralization test, recording a high antibody titre after 31 days. The cat improved after medical treatment and clinically recovered. This study suggests that exposure to SARS-CoV-2 could lead to a natural infection with bronchial pneumonia in cats along with a possible prolonged persistence of SARS-CoV-2 RNA in the upper airways, albeit at a low level. The cat developed neutralizing antibodies, reaching a high titre after 31 days. Further descriptions of SARS-CoV-2 naturally infected pets, their medical management and diagnostic findings would be useful to enhance knowledge about COVID-19 in susceptible animals.

Do modified live virus vaccines against bovine viral diarrhea induce fetal cross-protection against HoBi-like Pestivirus?

Bovine Pestivirus heterogeneity is a major challenge for vaccines against bovine viral diarrhea (BVD). In breeding herds, fetal protection is a high priority issue. To some degree, fetal infections in vaccinated heifers have been attributed to the antigenic diversity of bovine Pestiviruses. The purpose of this study was to assess fetal protection against a divergent bovine Pestivirus (Hobi-like Pestivirus, HoBiPeV) with a commercially available modified live vaccine (MLV) claiming fetal protection against BVDV 1 and BVDV 2 up to one year after the first inoculation. Five vaccinated and four unvaccinated heifers were challenged by intranasal inoculation with the HoBiPeV Italy-1/10-1 strain between 82 and 89 days after insemination, i.e. between 4 and 6 months after vaccination. At challenge, neutralizing antibody titers to HoBiPeV in vaccinated heifers were low or even undetectable. Of the four unvaccinated heifers, one control animal aborted (fetus not available) and the remaining three gave birth to HoBiPeV positive calves. Among the heifers of the vaccinated group, one aborted the fetus in the sixth month of pregnancy, which tested Pestivirus negative, while three others gave birth to healthy, HoBiPeV negative calves; the remaining heifer delivered one HoBiPeV positive calf. The results suggest that the BVDV vaccine might be able to elicit a partial fetal protection against HobiPeV, even in absence of a strong specific antibody response.

Persistence of Leptospira borgpetersenii Serovar Hardjo in Refrigerated Raw Milk: A Transmission Risk of Leptospirosis to Humans.

Leptospira borgpetersenii serovar Hardjo (LH) is an important infectious agent of reproduction pathologies and lactation decline in cattle, with a possible zoonotic role. To figure out the potential zoonotic risk for human raw-milk consumption, the present study aims at assessing the persistence and viability of LH in refrigerated raw milk over a 10-day period, which is set as the maximum time range for raw-milk domestic consumption. A negative sample of fresh raw milk was contaminated with an LH strain (2 × 108 Leptospires/mL) and analyzed by a rrs (16S) gene targeting real-time PCR (rPCR) protocol for LH DNA at days 1, 2, 3, 6, 7, 9, and 10. Seven aliquots of the same sampling time were inoculated into a semisolid EMJH media for bacterial culture. All aliquots tested positive in both rPCR and culture, which demonstrates that raw milk does not alter the detectability and viability of LH, respectively. The analytical sensitivity (LoD, limit of detection) determined for the rPCR (103 Leptospires/mL) was repeatable during the study, whereas it gradually decreased when it came to the bacterial culture. This study demonstrates that bovine raw milk might be a potential vehicle of infection by LH, even when storage conditions are strictly respected.

Detection of New Leptospira Genotypes Infecting Symptomatic Dogs: Is a New Vaccine Formulation Needed?

Leptospirosis in dogs has been largely described worldwide, and epidemiological studies have been mainly based on serological data. This study aims to detect and genotype leptospires affecting symptomatic dogs in Northeast Italy between 2013 and 2019. Overall, 1631 dogs were tested using real-time PCR, and leptospires from 193 dogs were subjected to Multilocus Sequence Typing and a Multiple Loci Variable-number Tandem Repeat Analysis. Leptospires were successfully isolated from 15 symptomatic dogs. Six distinct Sequence Types (STs) were found for 135 leptospires, with 3 STs characterizing Leptospira interrogans (ST17, ST198 and ST24), 2 STs characterizing Leptospira kirschneri (ST117 and ST289) and 1 ST characterizing Leptospira borgpetersenii (ST155), revealing the circulation of the serogroups Icterohaemorrhagiae, Australis, Sejroe and Pomona. The Multiple Loci Variable-number Tandem Repeat Analysis of 17 samples did not result in any additional discrimination. Genotypes were compared with those of strains present in the historical internal database, and possible transmission chains were identified from rat, mouse, hedgehog and pig. This work highlights the importance of molecular methods in revealing and identifying circulating Leptospira strains, and it also encourages the evaluation of the ability of commercially available vaccines to reduce the disease burden among dogs.

Genetic characterization of Neospora caninum from Northern Italian cattle reveals high diversity in European N. caninum populations.

Recent studies have revealed extensive genetic variations among Neospora caninum, a cyst-forming protozoan parasite that is one of the main causes of bovine abortion in the cattle industry worldwide. Previous genetic studies based on multilocus microsatellite genotyping (MLGs) of different Ibero-American populations showed a high genetic diversity. These studies provided clear clues of a predominant clonal propagation in cattle and population sub-structuring partially associated with geographical origin. Although, these reports were limited to a reduced number of countries. In this study, the N. caninum isolates from aborted bovine fetuses and stillbirths and a goat abortion from Northern Italy were investigated genetically using 9 microsatellite markers. Complete or nearly complete isolate profiles were obtained from 30 fetuses and stillbirths. An extensive genetic diversity was also found in this Italian N. caninum population. The study of genetic relationships among Italian MLGs using network (eBURST) and principal component analyses based on the allele-sharing coefficient (PCoA) showed different clonal subpopulations disseminated throughout Northern Italy without apparent segregation depending on the geographic origin, cattle breed, or time of collection. The presence of linkage disequilibrium supports a predominant clonal propagation of Italian N. caninum. In addition, most of Italian MLGs segregated from other global populations including Spain, Argentina, Mexico, Brazil, Germany, and Scotland, suggesting the existence of specific N. caninum subpopulations in the Northern Italy and different subpopulations of N. caninum circulating in Europe.

Prevalence and characterization of methicillin-resistant Staphylococcus pseudintermedius from symptomatic companion animals in Northern Italy: Clonal diversity and novel sequence types.

The aim of this study was to assess the prevalence, the genotypic diversity, the antimicrobial resistance traits of canine and feline clinical methicillin-resistant Staphylococcus pseudintermedius (MRSP) isolates in a diagnostic laboratory in Italy during 2015-2016. All isolates were characterized by multilocus sequence typing (MLST), staphylococcal cassette chromosome (SCC)-mec typing and staphylococcal protein A (spa)-typing. The resistance profiles were assessed by antimicrobial susceptibility testing and confirmed genotypically by the detection of mecA gene and by microarray analyses. The prevalence of MRSP isolates was high (31.6%). All the strains were multidrug resistant and the most frequent clone was ST71-SCCmec type II-III. These results confirm a high prevalence of MRSP amongst clinical samples from pets in Italy. These isolates show multidrug resistance features that are of concern both in veterinary and human medicine for clinical and epidemiological reasons.

Proposal for a new subtype of the zoonotic genotype 3 Hepatitis E virus: HEV-3l.

The near-complete genomic sequences of two hepatitis E virus (HEV) strains, detected from feces of infected pigs, were obtained. Phylogenetic analysis and p-distance comparisons of the complete coding regions showed a close relationship to the French swine strain FR-SHEV3c-like detected in 2006 (p-distance value 0.101), belonging to HEV-3 but not assigned to any known subtype. The three HEV sequences showed, relatively high nucleotide distances (p-distance >0.129) compared to the other defined HEV subtype references and unclassified strains. The HEV classification criteria and the high sequence similarity suggest that these strains can be assigned to a putative novel subtype of genotype 3, HEV-3l.

Complete nucleotide sequence of a novel bovine viral diarrhea virus subtype 1 isolate from Italy.

To gain further insight into the genomic features of bovine viral diarrhea virus 1 (BVDV-1) subtypes, we sequenced the complete genome of the BVDV-1 isolate VE/245/12. This is an uncommon subtype that was isolated from a persistently infected animal. Here, we report the complete genome sequence, consisting of 12,295 nucleotides (nt) with an open reading frame of 11,694 nt encoding 3,898 amino acids. Phylogenetic analysis of the full-length genome, 5'-UTR, and Npro region confirmed that the BVDV-1 isolate differed significantly from all of the bovine pestiviruses identified so far, providing evidence for the presence of a distinct novel genetic group.

Molecular characterization by MLVA of Coxiella burnetii strains infecting dairy cows and goats of north-eastern Italy.

Q fever is a worldwide zoonotic disease caused by Coxiella burnetii (C. burnetii), an obligate intracellular bacterium. In ruminants, shedding into the environment mainly occurs during parturition or abortion, but the bacterium is shed also in milk, vaginal mucus, stools and urine. In Italy few surveys have been conducted and reported seroprevalence values ranged between 10% and 60%, even if few human cases have been described. Genotyping of bacteria is crucial for enhancing diagnostic methods and for epidemiological surveillance. The objective of this study was to investigate genotypic differences of C. burnetii genotypes directly in 34 samples, collected during a 3-years survey among 11 dairy cattle and 11 goat farms in the north-eastern part of Italy using a 6-locus multiple loci variable number of tandem repeat analysis (MLVA) method. The samples analysed included 13 bulk tank milk (BTM), 6 individual milk, 11 vaginal swabs and 4 foetal spleens. MLVA-type 2 was determined as the most prevalent in cattle in this study. C. burnetii strains circulating in the studied cattle population are very similar to genotypes previously described, while genotypes from goats showed an important variability. Further investigation are needed to understand the reason of this pattern.

International trades, local spread and viral evolution: the case of porcine circovirus type 2 (PCV2) strains heterogeneity in Italy.

Porcine circovirus type 2 is one of the most widespread and economically relevant infections of swine. Four genotypes have been recognized, but currently, only three (PCV2a, PCV2b and PCV2d) are effectively circulating. The widespread livestock trade and rapid viral evolution have contributed to determining the high heterogeneity of PCV2 and the dispersal of potentially more virulent strains. Italian swine farming and the related processing industry are relevant in the national economy. Despite the noteworthy losses associated with direct and control measure costs, no data are currently available on the molecular epidemiology of PCV2 in Italy. Our study, which was intended to fill this gap, considered 75 completed genome PCV2 sequences, which were obtained from samples collected from the highly densely populated area of Northern Italy between 2007 and 2014. Phylogenetic analysis and comparison with reference sequences demonstrated the co-circulation, with different prevalences, of PCV2a, PCV2b and PCV2d within the national borders, with PCV2b being the most prevalent. Recombination between different genotypes was also proven to be frequent. Phylogeographic analysis demonstrated that the marked variability of Italian PCV2 strains can be attributable to multiple introduction events. The comparison of the phylogenetic analysis results, the location of different haplotypes and the international commercial routs of live pigs allow the speculation of several links as well as the role of Italy as both an importer and exporter of PCV2 haplotypes, mainly from and to European and Asian countries. A similarly intricate contact network was demonstrated within national borders, with different haplotypes being detected in the same province and different provinces harbouring the same haplotype. Overall, this paper represents the first description of PCV2 in Italy and demonstrates that the high variability of circulating Italian strains is due to multiple introduction events, wide circulation within national boundaries and rapid viral evolution.

IFAT and ELISA phase I/phase II as tools for the identification of Q fever chronic milk shedders in cattle.

Q fever is a widespread zoonotic disease caused by Coxiella burnetii. In cattle the bacterial shedding can persist without symptoms for several months and the shedders identification is a critical issue in the control of the infection at herd level. Following the example of the human protocols for the assessment of Q fever infection status, the aim of this study was the evaluation of the antibody response dynamics to phase I and phase II antigens in C. burnetii shedder dairy cows by means of a phase-specific serology, to verify the suitability of the investigated tools in recognising milk shedders. A total of 99 cows were monitored during time and classified on the basis of serological and PCR results in five groups identifying different shedding patterns. The 297 sera collected in three sampling times were tested by means of ELISA IgG for differential phase I and phase II antibodies detection, while a selection of 107 sera were tested by means of phase specific IgM and IgG IFAT. Both ELISA IgG and IFAT IgG highlighted a low reactivity in non-shedder seropositive animals compared to chronic milk shedder animals. ELISA IgG seemed to perform better than IFAT IgG-IgM, showing significant serological differences among groups that allowed recognising specific serological group patterns, in particular for chronic and occasional milk shedders. These results supported the hypothesis that an animal classification based on phase patterns is reasonable, although it needs to be further investigated.

Increased genetic diversity of BVDV-1: recent findings and implications thereof.

Sequence-based genotyping was recently used to distinguish between the BVDV-1 and BVDV-2 species of the bovine viral diarrhoea virus (BVDV). Quite recently, a new putative species, BVDV-3, was also detected. The phylogenetic analysis of the 5'-untranslated region (UTR) and Npro region has revealed at least 17 distinct subtypes for BVDV-1 to date. The aim of this study was to further investigate the genetic heterogeneity of BVDV-1 in Italy, by analysing 173 virus sequences from isolates collected over an 18-year period (1997-2014). Viral RNA was extracted from the original biological samples identified as BVDV-1-positive. Reverse transcription (RT) and polymerase chain reaction (PCR) assays targeting a 288-base pair (bp) region of the 5'-UTR and a 428-bp region encoding the autoprotease Npro were performed, and the RT-PCR products were sequenced. The phylogenetic analysis of the 5'-UTR and Npro sequences re-confirmed the circulation of ten out of eleven subtypes previously discovered in Italy. Interestingly, four isolates differed significantly from all of the bovine pestiviruses identified so far, thereby providing evidence for the circulation of three novel subtypes that have not been documented so far. The growing number of reports on BVDV-1 heterogeneity, including the recent findings reported herein, raises concern related to the emergence and spread of new BVDV variants, with possible implications for animal health and disease control. This global issue needs to be addressed with the highest priority.

Observation of high recombination occurrence of Porcine Reproductive and Respiratory Syndrome Virus in field condition.

Recombination in Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is a well-documented phenomenon. A high recombination frequency has been reported in experimental conditions both in vitro and in vivo, and its role in driving viral evolution has been postulated by several authors. However field evidences are rare, mainly obtained from large-scale sampling and typically represented by single sequences rather than by groups of circulating "recombinant progenies". The present work was aimed to investigate the gray area between experimental studies and large-scale epidemiological investigations. The study was performed on ORF5, ORF7 and concatenated sequences obtained in our laboratory or available in GenBank collected between 2009 and 2012 in northern Italy. Six independent recombinant strains out of 66 concatenated sequences (∼9%) were found, demonstrating a high recombination frequency respect to previous field studies but comparable to in vitro experiments. In silico analysis let speculate that this new strain displayed physicochemical features diverse enough to potentially alter its immunological properties. Taken altogether, the results of our study support previous experimental evidences that depict PRRSV to be extremely prone to recombination. The limited temporal and geographical spread of recombinant strains however states in favor of a limited fitness of the recombinant progeny compared to parental strains and the marginal role of this phenomenon in PRRSV evolution.