Reservoirs of Porcine Circoviruses: A Mini Review

Abstract

Porcine circovirus (PCV) is one of the smallest known DNA viruses in mammals. At present, PCVs are divided into three species, PCV1, PCV2, and PCV3. PCV1 and PCV2 were found in the 1970s and the 1990s, respectively, whereas PCV3 was discovered recently in 2016. PCV1 does not cause diseases in pigs. However, PCV3, similar to PCV2, is reported to be associated with several swine diseases, including porcine dermatitis and nephropathy syndrome (PDNS) and reproductive failure. PCVs are very common in domestic pigs as well as wild boars. However, PCVs have been occasionally isolated from non-porcine animals, including ruminants (such as cattle, goats, wild chamois, and roe deers), rodents (such as NMRI mice, BALB/c mice, Black C57 mice, ICR mice, Mus musculus, and Rattus rattus), canines (such as dogs, minks, foxes, and raccoon dogs), insects (such as flies, mosquitoes, and ticks), and shellfish. Moreover, PCVs are frequently reported in biological products, including human vaccines, animal vaccines, porcine-derived commercial pepsin products, and many cell lines. PCVs are also abundant in the environment, including water samples and air samples. Interestingly, PCV1 and/or PCV2 antibody or antigen has also been detected in sera, stool samples and respiratory swab samples of human, revealing zoonotic potential of PCVs. Thus, PCVs inhabit many types of reservoirs. In this review, we summarize the reservoirs of PCVs, and this information would be helpful in understanding the natural circulating status and possible cross-species transmission of PCVs.

Free to Circulate: An Update on the Epidemiological Dynamics of Porcine Circovirus 2 (PCV-2) in Italy Reveals the Role of Local Spreading, Wild Populations, and Foreign Countries

“…Its recent emergence as a major swine pathogen suggests the remarkable role of intensive swine farming in affecting PCV-2 epidemiology [9]. While swine is the primary host for PCV-2, other species have been reported as susceptible [10]. Nevertheless, wild boar seems to be the only other host in which PCV-2 is constantly detected and which could play a relevant role in PCV-2 epidemiology [11][12][13][14].…”

Lack of Evidence on the Susceptibility of Ticks and Wild Rodent Species to PCV3 Infection

“…Furthermore, previous studies reported rodents as possible spreaders of PCV infection [ 19 ]. For instance, PCV2 was proven to infect mice in experimental conditions and also synanthropic rodents that lived close to swine farms, where they could have been infected due to the direct contact with positive swine [ 24 , 25 , 26 ].…”

“…All this evidence is based on laboratory or synanthropic animals, likely exposed to a much higher infectious pressure, thus preventing any extension of these results to related wild species [ 16 , 19 , 24 ]. However, other authors have put emphasis on this potential part of the viral biological cycle and ecology based on our previous speculations [ 5 ].…”

“…Accordingly, PCV3, similar to other PCVs, shows plasticity in host tropism and has also been reported in nonporcine species such as dogs, ruminants and mice [ 15 , 16 , 17 , 18 ]. Moreover, previous studies on PCV2 and PCV3 demonstrated that arthropods and rodents could also be involved in the spread of these viruses [ 11 , 19 , 20 ]. Recent findings showed that roe deer, mouflon, fallow deer and chamois tested positive for PCV3 [ 11 , 21 ], but also two PCV3-positive Ixodes ricinus ticks were collected from PCV3-negative roe deer [ 11 ], which opens up interesting questions about the role of these arthropods as vectors in the PCV3 enzootic cycle in nature.…”

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“…PCVs are very common in domestic pigs as well as in wild swine population. However, PCVs have been occasionally isolated from non-porcine animals, including cattle, goats, wild chamois, and roe deers, mice, raccoon dogs, minks, foxes, and raccoon dogs, flies, mosquitoes, and ticks, and shellfish [24][25][26], Pigs are ordinarily the natural reservoirs of the virus. In this mini review, a snap shot of the historical aspects of porcine circovirus with emphasis on type 2 and its host preferences will be spotlighted.…”