2011, Vol. 6 No. 1, Article 73
PRRSV and PCV-2 Infections in Greek Swine Farms: Clinical forms and vaccination programmes
V. G. Papatsiros
Clinic of Medicine, School of Veterinary Medicine, University of Thessaly, 43100 Karditsa, Greece
*Corresponding Author; e-mail address: firstname.lastname@example.org
The presence of PRRS, in association with PRDC and PCV-2 Diseases (including mainly PMWS and PDNS), increased the cost of Greek pork meat production. During the last three years, a high number of PRRS cases in vaccinated farms were noticed with severe respiratory clinical signs in growing/finishing pigs and with moderate reproductive form in sows. These outbreaks can probably be due to the entrance of «new» PRRSV isolates in farms, which were more virulent and/or recombined with the pre existed isolates. PCV-2 Diseases including mainly PMWS and PDNS, continue to have a strong economical impact, probably by interaction or synergism with other respiratory pathogens, mainly with «new» isolates of PRRSV. PCVD increase the enteric and respiratory problems, reduce the growth rates and increase the mortality rates in weaning and growing pigs. Furthermore, during the last years, even more reproductive disorders in breeding stock resulting from PCV-2 have been recorded. Mass vaccinations against PRRSV and PCV-2 in sows and suckling or weaning pigs have beneficial effects in Greek swine farms, improving their health status, reproductive performance and productivity.
Greece, PRRSV, PCV-2, PCVD, vaccine, sow, pig.
The clinical manifestations of Porcine Reproductive and Respiratory Syndrome (PRRS) vary from subclinical to severe reproductive and/or respiratory symptoms (Halbur et al., 1996). The severity of PRRSV associated disease may result from a number of factors such as differences in virulence among PRRSV isolates (Halbur et al., 1996), probable recombination between the different isolates that are responsible for the clinical manifestation of PRRS within the same farm (Done and Paton, 1995), differences in concurrent infections (other viruses and bacteria) and hygiene monitoring programme (Goldberg et al., 2000). Furthermore, the PRRS virus (PRRSV) is involved in aetiology and/or pathogenesis of Porcine Respiratory Disease Complex (PRDC) and PCV-2 Diseases (including mainly Postweaning Multisystemic Wasting Syndrome, PMWS and Porcine Dermatitis and Nephropathy Syndrome, PDNS) (Kennedy et al., 2000; Harms, 2002). In cases of PRRS co-infections with other agents, the cost of pork meat production raises due to the necessity of treatments and other special management strategies. This communication aims to present the clinical manifestations of PRRS in the Greek swine industry, through the presence of PCV-2 and other co-infections, as well as the relevant vaccination programmes.
HISTORICAL BACKGROUND OF PRRSV AND PCV-2 INFECTIONS IN GREECE
In Greece, PRRS was first detected in 1993 (Xilouri - Frangiadaki 1993; Kyriakis et al., 1996) with an acute phase and then with symptoms such as respiratory problems in growing/finishing pigs (especially during winter), viral – bacterial enteric diseases, acute deaths, meningitis, arthritis, etc. Up to day, PRRSV appears in an enzootic form (independently of the season) with elevations and declines of reproductive problems in breeding stock (premature farrowing, abortions, increase in rates of infertility, returns to oestrus, postpartum dysgalactia syndrome), causing tremendous economic losses. In the Greek swine industry, PRRSV is a primary pathogen agent in the growing/finishing pigs’ mortality (Balkamos, 2004). Furthermore, the mortality of growing/finishing pigs is significantly lower in swine farms that are not infected by PRRSV than those infected by PRRSV. During the last years, the presence of PRRS, together with the appearance of new syndromes such as PRDC, PMWS and PDNS caused additional economic losses (Saoulidis et al., 2002; Georgakis et al., 2002). In Greece, PCV-2 Diseases were first detected in 2000 (Saoulidis et al., 2002). Clinical signs, gross post-mortem changes and histopathological changes observed in infected pigs, were similar to those previously described for both PDNS and PMWS (Kennedy et al., 2000; Harms, 2002). Additionally, the genetic analysis of the first PCV-2 isolates from pigs presenting various clinical conditions in Greece has been performed (Sofia et al., 2003). In a large scale field study in Greek swine farms, the causes of death in growing/finishing pigs were examined and it was observed that the most frequent causes of death (48.21%) were complex infections of the respiratory system. It was also noticed that Mycoplasma hyopneumoniae (63.16%), PRRSV (26.03%) and Swine Influenza virus (8.55%) played a big role as primary pathogens, while the cause of death was probably the result of complications by secondary bacterial pathogens (Βalkamos, 2004). Among them, Pasteurella multocida (21.19%), Actinobacillus pleuropneumoniae (7.81%), Streptococcus suis (4.09%) and Haemophilus parasuis (1.49%) were identified (Βalkamos et al., 2002).
CLINICAL FORMS OF PRRSV AND PCV-2 INFECTIONS IN GREECE
During the last three years, PRRS caused severe losses in the Greek swine industry. A significant number of cases in vaccinated against PRRS farms, where gilts or piglets were kept without the proper preventive facilities of biosecurity as quarantine, serology examinations etc. was noticed. The syndrome appeared in growing/finishing pigs in the form of severe respiratory clinical symptoms, resulting in substantial economic losses due to the increase of mortality, poor growth rates and use of expensive treatments, including mainly antibiotics. In some cases, clinical signs of PRRS were of less importance than of those resulting from the outbreaks of other various bacterial diseases such as the Glässer disease and pneumonia due to Mycoplasma hyopneumoniae or Actinobacillus pleuropneumoniae, Bordetella bronchiseptica and Pasteurella multocida. These outbreaks could probably be due to the entrance of «new» PRRSV isolates from the introduction of replacements gilts or piglets. Apparently, as it was noticed by clinical signs and losses, these «new» isolates were more virulent and/or recombined with the pre existed isolates. Unfortunately, the ability of PRRSV to persist in herds and the wide biological, antigenic and genetic variability of PRRSV may further complicate control plans (Goldberg et al., 2000). In cases with severe respiratory symptoms in growing/finishing pigs and of lack or moderate reproductive form of PRRS, the probable cause was either that the sows’ vaccination against PRRS did not protect the growing/finishing pigs or that the «new» isolates of PRRSV had more respiratory than reproductive tropism. It could also be the coexistence of all the above mentioned cases. Up to day, PCV-2 Diseases (PCVD) including mainly PMWS and PDNS, continue to have a strong economical impact on the Greek swine farms, since they remain an important risk factor for PRDC, probably by interaction or synergism with other respiratory pathogens, mainly with «new» isolates of PRRSV. PCVD increase the enteric and respiratory problems, reduce the growth rates and increase the mortality rates in weaning and growing pigs. The above clinical signs are often related to secondary infections, including mainly Glasser’s disease, E. coli infections, Staphylococcal skin infections, Enzootic Pneumonia and other bacterial pneumonias. In many cases, Mycoplasma hyopneumoniae, a common finding in PCVD incidences, increases the incidences and the severity of PCVD in pigs (Kyriakis et al., 2002). During the last years, even more reproductive disorders in breeding stock, as abortions, return to oestrus, mummified and stillborn piglets resulting from PCV-2 have been recorded (no published data). Moreover, during last 2 years, clinical observations in field conditions suggest that when PCVAD is present on a farm, more pigs with ear tip necrosis are observed. Pigs of 3-10 weeks of age are affected through out of different batches accompanied with lesions of PNES, severe wasting, respiratory clinical signs and significant mortality (Papatsiros, 2011).
PREVENTIVE AND CONTROL STRATEGIES USING VACCINES
In field studies in Greece, the use of PRRSV inactivated vaccines in sows / gilts, in closed single-site farrow-to-finish farms with persistent PRRSV infection and high seroprevalence, proved to reduce the negative effects of the virus on the breeding herds (Papatsiros et al., 2006 a,b). The vaccination led to an improvement of the sow reproductive performance (increase of the farrowing rate and decrease of the abortion, premature farrowing, return to service and culling rates) and of their litters’ characteristics (decrease of the number of mummified, weak, light weight and “splay-legs” piglets/litter and increase of the number of live born, alive 24 h after birth and weaned piglets/litter). Moreover, the long-term vaccination of boars with the same inactivated vaccine was safe and no changes in semen characteristics after each vaccination were noticed (Papatsiros et al., 2008). In similar field studies in Greek farms, PRRSV Modified Live Vaccine (MLV in gilts at the age of 180 days and sows 10 days post-partum) resulted in the improvement of the health status and performance of gilts/sows and their litters, as shown by the reduction of sows with premature farrowing due to PRRSV, by the lower return-to-oestrus rate and prevalence of sows with post-partum dysgalactia syndrome, the higher farrowing rate and number of piglets born alive per litter, the lower number of dead and mummified born piglets and the higher number of piglets weaned per litter (Alexopoulos et al., 2005). Furthermore, in farms affected by both PRRS and PMWS, the use of same MLV vaccine in piglets at 35 days of age resulted in a significant reduction of clinical signs of PMWS (Alexopoulos et al., 2003). Recently, similar results are published by Genzow et al (Genzow et al. 2009). Additionally, the use of the same MLV vaccine in sows and their fattening pigs (at 35 days of age) on farms with both PMWS and PRRS, led to an improvement of average daily gain and feed conversion ratio in vaccinated piglets and reduction of morbidity in the growing pigs (Kritas et al., 2007). However, recently evidences based on my experience and field conditions observations indicate that the use of this MLV vaccine in piglets at 2 weeks of age has beneficial results in their mortality rate and growth performance. Moreover, the use of the same vaccine in breeding stock at 6th day of lactation and at 60th day of pregnancy(in farms with acute outbreaks of PRRS or endemic PRRS form with 4-5 outbreaks every year, as well as in large scale farms with a capacity of over 700 sows under production) or at 2-4 weeks before mating and revaccination before each consecutive gestation or at random at 4 month intervals (in farms with chronic PRRS form with 1-2 outbreaks every year or with a capacity of over 100-200 sows under production) improves the reproductive performance together with the viraemic status and growth rates of the piglets (no published data)It is also recommended to use the proper vaccination program against Mycoplasma hyopneumoniae (one or two shot vaccinations) in farms suffering from respiratory syndrome due to Enzootic Pneumonia, PRRS and PMWS, in order to control efficiently Enzootic Pneumonia without risking to enhance losses due to PMWS (Alexopoulos et al., 2004)Mass vaccinations against PCV-2 in sows and weaning pigs in Greek swine farms have recently started. The vaccination of the sows seems to have, up today, positive effects as it prevents PMWS mortality from farrow to finish, as high numbers of specific antibodies which could be transferred to their piglets via colostrums, decreases mortality in piglets, improves growth and performance of the piglets and generally improves the growth rate of pigs. Additionally, the use of vaccines in pigs at 3 weeks of age or older seems to prevent viremia (presence of virus in the blood and lymphoid tissues), significantly decreased nasal and faecal shedding of the virus, decrease the mortality rates and use of treatments in nursery (e.g. antibiotics), but also reduces weight loss associated with PCV-2 infection during the fattening period. Nowadays, PRRS and PCV-2 infections are dangerous risk factors for the Greek swine industry and for this reason, it is important to apply all preventive facilities, such as vaccinations, reduction of the introduction gilts and maintenance of a grandparent nucleus in the farm for producing gilts, quarantine and serological monitoring for all introduced animals (gilts and piglets), as well as the purchase of animals from PRRSV- negative farms. In conclusion, the most efficient and economical tool to control and prevent PRRS and PCVD is the application of appropriate vaccination programmes.
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