Porcine Circovirus 2

ABSTRACT
Porcine circovirus type 2 (PCV2) has a place with the viral family Circoviridae and the genus Circovirus. Circoviruses are little, single‐stranded nonenveloped DNA infections that have an unsegmented round genome. PCV2 is the essential causative specialist of a few conditions by and large known as a porcine circovirus‐associated disease (PCVAD). A large number of the conditions related with PCVAD are a consequence of coinfection with PCV2 infection and different operators, for example, Mycoplasma and porcine conceptive and respiratory disorder infection. PCV2 disease is available in each significant pig delivering nation on the planet, and the quantity of recognized instances of PCVAD is quickly expanding. In the United States, the sickness has cost makers a normal of 3–4 dollars for every pig with top misfortunes going as much as 20 dollars for each pig. The significance of this malady has animated examinations pointed toward distinguishing hazard factors related with disease and limiting these dangers through changed administration rehearses and the advancement of inoculation techniques. This paper gives a review of current information identifying with PCV2 and PCVAD with an accentuation on data pertinent to the pig veterinarian.

Keywords: Infectious diseases, Immunohistochemistry, Viral virulence mechanisms.

INTRODUCTION
Circoviruses, the littlest of the infections of vertebrates, are 17-22 nm in breadth. Porcine circovirus was first portrayed in 1974 as a picornavirus- like pollutant of the persistent pig kidney cell line PK/15. Trial challenge recommends kidney cell line PK/15. Test challenge recommends that this infection, named porcine circovirus 1, is non- pathogenic. An antigenically and genomically particular circovirus, porcine circovirus 2 (PCV 2), is reliably disconnected from piglets with post – weaning multisystemic squandering disorder (PMWS). Sero- epidemiological examinations demonstrate that disease with PCV 2 is far and wide in pig populaces around the world. The infection has likewise been connected to porcine dermatitis and nephropathy disorder (PDNS) and furthermore to regenerative issues. Three genotypes are perceived, PCV – 2a, PCV – 2b and PCV – 2c. Porcine circovirus 2 is an antigenetically particular infection initially secluded in France in 1997. It has been secluded from youthful pigs with squandering sickness disorder in Canada, the United States, Spain, Denmark, and Northern Ireland. By grouping examination, disengages of this infection from various nations are 96% comparable yet under 80% like porcine circovirus 1.

VIRUS PROPERTIES
Little, non – wrapped, single – abandoned DNA infections with icosahedral evenness

• Replicate in the core of separating cells
• Stable in the climate
• Circoviruses cause infection in chickens, psittacine feathered creatures and pigs.
• Serologic evaluations show that PCV2 is broad in pig, freed from the PCV2-SD popularity of the ranch. Outcomes from evaluate serologic investigations display that PCV2 has been contaminating pigs for >50 years up until now, and phylogenetic examinations reveal that PCV2 has most possibly flowed in pigs during the previous a hundred years.
• First of all, PCV2-SD became identified in excessive wellbeing crowds that had been liberated from maximum simple pig microbes. Anyhow, beneath area conditions, pig that provide warning signs of PCV2-SD usually are contaminated with distinct specialists, which includes porcine parvovirus, porcine conceptive and respiration disorder infection, Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Pasteurella multocida, Haemophilus parasuis, Staphylococcus spp, and Streptococcus spp.
• PCV2 can imitate in babies simply as in zona pellucida–free undeveloped organisms. Additionally, an analysis with undeveloped organisms offered to PCV2 and afterward moved to receptor vegetation recommended that disorder can set off early stage passing. On this way, it’s miles regular that one of the in all likelihood consequences of PCV2 contamination in sows can be re-visitation of estrus. Transplacental transmission of PCV2 has been illustrated. Anyhow, tests using pregnant sows vaccinated intranasally have yielded variable outcomes. On the point when fruitful, those investigations have indicated that PCV2 may additionally reason fetal loss of life, like that of porcine parvovirosis, with live pigs along with lifeless piglets and mummies of numerous sizes.
• PDNS is viewed as a kind III touchiness reaction wherein the antigen present in the invulnerable buildings is obscure. It has been theorized that PCV2 will be the antigen, yet there’s no conclusive confirmation that PCV2 reasons PDNS sores. Backhanded evidence exists, as an example, altogether better serum neutralizer titers to PCV2 in prompted pigs contrasted and sound or PCV2-SD-prompted pigs.
• Haemagglutination contemplates – No haemagglutination motion was recognized with PCV.
• Resistance to pH3 – The titres of the PCV and PPV pools attempted have been unaffected after advent. The titre of the ADV pool became fundamentally diminished.
• Chloroform affectability – The infectivity titres of the PCV and PPV swimming pools stayed unaltered, even though ADV infectivity changed into completely inactivated.
• Heat solidness – The infectivity titres of the PCV and PPV pools stayed unaltered at the same time as ADV infectivity was appreciably reduced.
• PCV and CAV mild thickness considers – manifestly characterized tops were diagnosed using ELISA, one containing PCV antigen (thickness 1.36-1.37 g/ml CsCl) and the alternative CAV antigen (1.33-1.34 g/ml CsC1). Infectivity titres for PCV corresponded appropriately with PCV ELISA readings.
• PCV and CAV sedimentation coefficients – The sedimentation coefficients (S) of PCV and CAV were resolved from the separation went with the aid of every contamination, applicable to the introduced estimations of 155s for impossible to resist infection and 75s for the procapsid debris of BEV (PUTNAK and PHILLIPS, 1981). PCV changed into found to residue at a rate slower than that of the BEV procapsid particles with an anticipated estimation of 57s. CAV sedimented with a better assessed estimation of 91s.

PREVALENCE
PCV2 is regarded as a pervasive contamination in countries with and with out PCVDs, which includes PCV2-SD. PCV2 contamination and PCV2-SD have likewise been depicted in wild pigs. The disease has been accounted for round the arena.

Prevalence of PCVAD by sort of activity, farm size, and year.

TRANSMISSION

• PCV2 can be communicated in a few extraordinary approaches. The precept route is via oro‐nasal contact with tainted dung, contact with infected pee, or straightforwardly with tainted pigs. PCV2 is shed in respiratory emissions, oral discharges, urinary emissions, and excrement in each clinically encouraged just as in tainted yet glaringly sound pigs. Clinically motivated pigs shed contamination in higher amount contrasted and infected yet clinically sound pigs. PCV2 can likewise be communicated vertically (from the sow to the piglets) via the placenta causing industriously infected piglets upon coming into the world; however this strategy for transmission has all of the earmarks of being uncommon. PCV2 has likewise been demonstrated to be shed in colostrums; however whether this could result in a contamination is as but being researched. Ongoing paintings has indicated that PCV2‐inflamed red meat gadgets (lymphoid tissue, skeletal muscle, and bone marrow), when taken care of to gullible piglets for three days, added about viremia and seroconversion to PCV2 in the entirety of the piglets.
• PCV2 is likewise shed in semen and in trial considers authentic contamination dropping was diagnosed as right on time as 5 days postinoculation. Shedding in commonly tainted hogs has all of the earmarks of being low and sporadic.The maximum noteworthy degree of contamination suggests up in the unique liquid and nonsperm fraction.Boars which might be relentlessly contaminated may additionally keep on shedding the contamination in semen and semen tests had been determined to be high-quality in pigs as long as 71 weeks antique sufficient. Assessments collected from pigs jogging from seventy one to 149 weeks old sufficient were no longer located to shed contamination in semen. The infection didn’t seem to influence the quotes of live and morphologically ordinary sperm. Ongoing evidence has indicated that PCV2 infection gift inside the semen is irresistible when infused IP into pigs, however left out to seroconvert gilts that were misleadingly inseminated. Likewise, all pigs conceived of the gilts have been negative for PCV2 antibodies.
• The brooding length in tentatively contaminated pigs ranges from 2 to approximately a month. Once inside the host, PCV2 first contaminates the tonsils and lymph hubs of the top and starts replicating.PCV2 likewise taints B cellsthat likely causes scattering throughout the frame with the aid of the lymphatic framework. PCV2 has been diagnosed within the spleen, Peyer’s patches, and severa lymph hubs. PCV2 at that factor begins imitating in T cells and fringe blood mononuclear cells. Viremia in pigs is noticeable somewhere within the range of seven and 14 days postinoculation. PCV2 can motive a not on time infection, with viral DNA substantial in pigs as long as 125 days postinoculation in exploratory sicknesses.
• Transmission might be by using direct contact with tainted pigs. PCV2 has been identified in nearly all ability discharge courses, as an instance, nasal, visual, and bronchial emissions; spit; pee; and excrement. The contamination may be found in semen, but the viable importance of this is maximum probable beside the point. Planned impregnation (AI) of sows with PCV2-tainted semen from tentatively vaccinated hogs did not result in sow contamination or fetal disease. Nevertheless, whilst such AI was done with PCV2-spiked semen, regenerative troubles have been created. Along these strains, it seems to be that conceptive illness connected to AI is doable, yet simply whilst semen has a excessive contamination load, that is a long way-fetched underneath ordinary conditions. In spite of the truth that not illustrated, it’s far anticipated that touch with debased fomites, presentation to defiled feeds or biologic items, severa usage of hypodermic needles, or gnawing insects may also anticipate a characteristic in transmission.
• PCV2 may also keep in pig for a while below either take a look at or area conditions. Recovery pig may bring infection for broadened periods and be massive in ailment transmission. PCV2 is certainly impervious to commonly utilized disinfectants and to mild, likely permitting it to gather within the weather and be infective for brand spanking new gatherings of vulnerable pigs if thorough smooth measures are not accompanied. The decrease of colostral counter performing agent titer in pigs is associated with starting of PCV2-SD in past due nursery or completing pigs. Transplacental disorder with PCV2 has been said, yet it is not found out whether or not pigs infected in utero can therefore create medical PCV2-SD.
• Some reports have proposed that creatures apart from pig is probably tainted with PCV2 or PCV-like infections. Be that as it may, results of serologic investigations for immune reaction in opposition to PCV in steers and other animals had been conflicting, and trial recognition of malady utilizing PCV1 or PCV2 in forms of domesticated animals apart from pig has not been powerful. Mice might have the choice to recreate and maintain the contamination.

PATHOGENESIS

• The articulation of clinical ailment in pigs contaminated with porcine circovirus regularly includes optional microbial porcine circovirus normally includes auxiliary microbial contaminations that may legitimately or in a roundabout way impact the sort of infection communicated.
• Infections that seem to upgrade the replication and pathogenicity of porcine circovirus 2 incorporate porcine parvovirus, pig flu infection, porcine conceptive and respiratory disorder infection, M. hyopneumoniae, and likely others. For instance, force teno sus infections (TTSuVs).
• The pathogenesis of PCVADs. The basic component of these diseases is insusceptible enactment, which some way or another improves the replication of porcine circovirus 2 out of an assortment of target cells. In this manner, PCVADs are clearly exacerbated by the immunostimulation that outcomes from coinfecting microorganisms, or even from the immunostimulatory activity of adjuvants, for example, keyhole limpet hemocyanin.
• However, resistant concealment by corticosteroids may likewise bring about expanded articulation of infection; subsequently the pathogenesis of these circovirus-related maladies in pig is exceptionally intricate.
• Furthermore, porcine circovirus 2 may itself regulate the host antiviral reaction as the viral genome contains an interferon-invigorated reaction component arrangement, which, when present with regards to unblemished infection however not in isolation,plays a likely part in viral pathogenesis in pig.
• The PCVAD recognized as postweaning multisystemic squandering disorder is described by individual to blending foci of granulomatous irritation in lymphoid tissues, lungs, liver, kidney, heart, and intestines,sometimes with noticeable “botryoid” consideration bodies in infection contaminated macrophages.
• Lymphoid consumption and colorful granulomatous irritation are trademark sores in lymphoid tissues of porcine circovirus 2-contaminated pigs. Porcine dermatitis nephropathy disorder has additionally been related with porcine circovirus 2 disease, and is additionally described by infarctive (ischemic rot) skin sores, especially on the back legs.
• The kidneys of influenced pigs display vasculitis and glomerulonephritis; in any case, porcine circovirus 2 antigens or nucleic corrosive are once in a while shown in these sores so a direct causal connection between porcine circovirus 2 disease and this dermatitis nephropathy condition is deficient. In outline, the pathogenesis of the different PCVAD conditions isn’t all around described, including the part of coinfecting microorganisms and immunemediated instruments of tissue injury.

CLINICAL SIGNS

• PCV2-SD is defined via clean weight reduction. Illness frequently occurs inside the swelling gadgets in pigs eight–18 wk vintage, in spite of the reality that the sickness can be likewise determined in greater installed or greater youthful pigs. Grimness is frequently 5%–20% among accomplices inside the overdue nursery or finishing stages. Mortality in pig with indicators of PCV2-SD can sporadically be >50%. However dying misfortune, PCV2-SD in finishing pigs might also make a vast increment in time arrive at marketplace weight, bringing about economic misfortune. Development impediment, squandering, and dyspnea are the scientific symptoms seen maximum frequently in episodes. Paleness, pallor, jaundice, unfastened bowels, and obvious inguinal lymphadenopathy likewise are located in a few inspired pigs. A 2nd charge fever (104°–106°F [40°–41°C]) that endures a few days might be regarded too. Congestion, helpless air pleasant, poor air alternate, and mixed age bunches appear to intensify the direction of the infection. Normally, simply more than one pigs in a gathering display squandering. The start of disease is probably severe, prompting passing interior more than one days in sure pigs. One of a kind pigs show a greater consistent sickness and neglect to place on weight or flourish.
• PCV2-SI is customary to happen in pigs that emerge as infected with the contamination and experience the ill consequences of improvement impediment (basically lower ordinary every day weight benefit [ADWG]) but not clean clinical signs and symptoms. Truth be told, in a ranch stimulated by way of PCV2-SD, a variable extent of pigs built up the essential malady, at the same time as most had just subclinical sickness. PCV2-SI were overlooked for a long term until the coming of immunizations brought on to be aware this situation. Immunized pigs have an expanded ADWG contrasted and nonvaccinated, glaringly sound companions. Such distinction has been displayed to shift between 10−40 g/d, contingent upon the ranch.
• PCV2-RD portrayed by overdue-time period premature births and stillbirths within the nonattendance or presence of other superb conceptive microbes is by way of all debts the sign of scientific PCV2 contamination in flowers. The extra a part of those depictions originate from North the usa and commonly occur in hearth up corporations. Re-visitation of estrus because of undeveloped dying as a likely result of intrauterine PCV2 ailment has been proposed depending on exploratory facts. However, there are no subject records unequivocally helping this effect.
• PDNS might also have an impact on nursery and growing pigs and, unevenly, grown-up creatures. The commonness of the condition in stimulated companies is commonly low (<1%), albeit higher prevalences (>20%) have been portrayed sporadically. Pigs with critical excessive sickness kick the bucket inner a couple of days after the start of medical signs and symptoms, because of excessive renal sadness with a noteworthy increment in serum tiers of creatinine and urea. Enduring pigs will in preferred get well and put on weight 7–10 days after the begin of the circumstance. Influenced pigs have anorexia, despair, give up, hardened step or probably hesitance to transport, and ordinary temperatures or mild fever. The maximum clean register the intense level is the presence of sporadic, purple-to-purple macules and papules on the pores and skin of the hindlimbs and perineal territory, regardless of the reality that stream is probably summed up in severely inspired creatures. With time, the sores emerge as secured through dim outsides and blur little by little (regularly in 2–three wk), occasionally leaving scars.

PATHO–MORPHOLOGICAL FINDINGS

Lesions

• PCV2-SD is analyzed by way of trademark histopathologic discoveries in encouraged pigs. Extraordinarily, lymph hubs might be generously amplified and faded on cut surface, the thymus decayed, and the tonsils more slender than usual. Splenic infarcts likewise might be to be had in a low quantity of pigs inspired with PCV2-SD. Histopathologic lymphoid sores are trademark, demonstrating lymphocytic exhaustion and granulomatous inflammation, now and again with the presence of multinucleate goliath cells and amphophilic botryoid intracytoplasmic attention collections of numerous sizes brought approximately by gathering of PCV2 debris.
• Lesions inside the lung are simple in motivated pigs; their seriousness is laid low with length of contamination and presence of simultaneous contaminations. Net lung sores can also include lack of ability to fall, immovability, diffuse aspiratory edema, mottling, and combination. Infinitesimally, a variable degree of lymphohistiocytic interstitial pneumonia to granulomatous bronchointerstitial pneumonia with bronchiolitis and bronchiolar fibrosis can be seen.
• Grossly, the liver might also seem icteric or potentially atrophic in a low volume of encouraged pigs. Interlobular connective tissue is probably conspicuous. Tiny accidents run from single mobile putrefaction (apoptosis) with mellow lymphocytic penetration of entrance zones to huge lymphohistiocytic periportal hepatitis with diffuse rot of hepatocytes. The kidneys might be broadened and show dissipated to diffuse white foci on the cortical surface. Tiny accidents include interstitial lymphohistiocytic penetration. Distinctive sores seen in stimulated pigs incorporate gastric ulceration (maximum likely due to a limited quantity to a drawn out stuffing period in continuously encouraged pigs) and incidental multifocal lymphohistiocytic myocarditis. In seriously inspired pigs, lymphohistiocytic penetrates can be seen in essentially all tissues.
• PCV2-SI pigs do not show internet injuries because of PCV2 disease. Those creatures can also display minute lymphoid accidents like those discovered in pigs with PCV2-SD, albeit just to a gentle degree.
• In PCV2-RD, stillborn and nonviable neonatal piglets show constant aloof blockage of the liver and cardiovascular hypertrophy with multifocal territories of myocardial staining. The important thing histopathologic highlight is fibrosing or probably necrotizing myocarditis in babies.
• PDNS is whatever but difficult to apprehend from a medical attitude due to the pink-to-dull macules and papules, which relate infinitesimally to putrefaction and discharge auxiliary to necrotizing vasculitis of dermal and hypodermal vessels and arterioles. Necrotizing vasculitis is a foundational consist of, but it’s miles more sizeable inside the skin, renal pelvis, mesentery, and spleen (splenic infarcts may additionally likewise be available due to necrotizing vasculitis of splenic guides or arterioles). Apart from pores and skin sores, pigs that kick the bucket intensely with PDNS have firm, respectively amplified kidneys, with a pleasant granular cortical surface and edema of the renal pelvis. The renal cortex suggests severa, little, ruddy pinpoint sores, like petechial hemorrhages, which minutely compare to amplified and irritated glomeruli (fibrinonecrotizing glomerulitis). Histologically, a moderate to excessive nonpurulent interstitial nephritis with enlargement of renal tubules is additionally found. Typically, each skin and renal sores are to be had, however sometimes, skin or renal injuries may happen on my own. Lymph hubs might be amplified and crimson because of blood waste from inspired zones with hemorrhages (predominantly pores and skin). Histopathologically, PCV2-SD–like sores, as an example, lymphocyte exhaustion and histiocytic as well as multinucleate monster mobile penetration (albeit less severe) are commonly found in lymphoid tissues of encouraged pigs, no matter the fact that to a milder diploma.

DIAGNOSIS

• The diagnosis of PCVAD depends on medical symptoms and display of PCV2 antigen in more than 1 lymphoid tissue, or 1 lymphoid tissue and 1 different organ framework, as an instance, the lungs, liver, kidney or digestive tract, or in 2 organ frameworks. In the event that antigen is discovered uniquely in 1 organ framework, at that factor the contamination is taken care of dependent on that organ framework. At the off risk that solitary confined PCV2 antigen is determined however there are excessive injuries, it’s far delegated continual serious PCVAD. Scoring of sores and the degree of antigen in tissues considers arranging of infection. End can be likely made depending on medical symptoms. In a observe of ranches encountering PCVAD illness, the fee that watched the accompanying clinical symptoms included squandering (ninety eight.1%), the runs (77.2%), dyspnea (seventy five.1%), lymphadenopathy (44.8%), focal neurologic signs (39.6%), jaundice (37.1%), inappetence (90.4%), and passing (ninety six.8%).
• Detection of PCV2 antigen or nucleic corrosive is viewed as the highest satisfactory degree for the conclusion of PCVAD. The satisfactory assessments for this are polymerase chain response, in situ hybridization (ISH) and IHC. There is proper now no data on affectability and particularity of those assessments, yet IHC offers more intense recoloring and is regarded as extra delicate, yet much less express than ISH. IHC is additionally much less steeply-priced to run and has a quicker pivot time. Anyhow, severa labs do not offer IHC, in light of the truth that one of the essential reagents is anti‐PCV2 antiserum. Albeit a monoclonal anti‐PCV2 is monetarily on hand, complete dedication can at gift be tough with that item. The most best approach to research PCVAD is the recognizable evidence of the trademark accidents of the disease. Minute injuries associated with PCVAD incorporate syncytial cells in lymph hubs, Peyer’s patches, and the lamina propria of intestinal manor. Additionally, macrophages have strongly outlined, spherical, basophilic cytoplasmic consideration our bodies.
• Serology can likewise be carried out and is a helpful method for distinguishing presentation to PCV2 for massive portions of pigs. In any case, it need to be recollected that severa clinically sound pigs are seropositive. Special assessments which have been created incorporate immunofluorescence check, IgM immunoperoxidase monolayer look at, enzyme‐connected immunosorbant degree, contamination separation, electron microscopy, and serum contamination balance tests. There’s at present no discipline take a look at for the dedication of PCVAD.
• Because porcine circovirus 2 is far attaining in pig populaces and often causes subclinical illnesses, the conclusion of PCVADs requires cautious assessment of the diploma of contamination in singular pig with the aid of quantitation of the variety and conveyance of infection tainted cells by using immunohistochemistry, or probably famous burden with the aid of ongoing (quantitative) PCR.
• The symptomatic method of PCV2-SI is of less enthusiasm for clinicians, due to the fact that absence of obvious clinical signs and symptoms in addition to showing of contamination by using PCR might be sufficient to build up any such willpower. Estimations of >one zero five or 106 PCV2 genome duplicates/mL of serum more often than not have been connected with the subclinical contamination.
• The realization of PCV2-RD must incorporate the accompanying guidelines: 1) late-term premature births and stillbirths, here and there with hypertrophy of the fetal coronary heart, 2) wide fibrosing or probably necrotizing myocarditis, and three) excessive centralizations of PCV2 inside the myocardial injuries and other fetal tissues. Differential judgments for PCV2-RD incorporate PRRS, porcine parvovirus, pseudorabies (Aujeszky contamination), leptospirosis, and extraordinary illnesses that purpose past due untimely births, stillbirths, and frail piglets. Up till now, there are not any conventional models to analyze a putative re-visitation of estrus associated with PCV2 infection. Nonetheless, the occasion of such symptoms in conjunction with evidence of viral dissemination at some stage in the clinical scene ought to be illustrated.
• The case definition for PDNS is reasonably straightforward and includes two essential requirements: 1) presence of hemorrhagic and necrotizing skin sores, basically situated at the hindlimbs and perineal sector, and moreover swollen and pale kidneys with summed up cortical petechiae, and a pair of) presence of foundational necrotizing vasculitis just as necrotizing and fibrinous glomerulonephritis. From a demonstrative perspective, discovery of PCV2 is excluded from the symptomatic policies.
• Differential locating of PDNS relies upon the maximum important pathologic end result. Cutaneous symptoms might be incorrect for classic and African pig fever, pig erysipelas, septicemic salmonellosis, sickness with Actinobacillus suis, porcine pressure condition, tour erythema (pee sopping wet flooring, synthetic consumes, and so on), and other bacterial septicemias. Differential conclusions for kidney sores include traditional and African pig fever, pig erysipelas, and septicemic salmonellosis. Serum biochemical examinations may additionally help separate PDNS from extraordinary infections; urea and creatinine focuses are uniquely accelerated.

CONCLUSION
It is realized that the majority of the pigs mount powerful insusceptible reactions to clear or breaking point PCV2 contamination. Nonetheless, an extent of pigs will be unable to check the contamination and create malady. These days, the ailment weight can be constrained by proficient immunization. This examination portrays significant contrasts in the improvement of the humoral resistant reaction between pigs that get subclinically contaminated with PCV2 and pigs that experience an elevated level of PCV2-replication which in 3 of 4 tests prompted the advancement of PMWS. These perceptions may add to a superior comprehension of the pathogenesis of a PCV2-disease.

REFERENCE

• Allan, G.M. and Ellis, J.A. (2000). Porcine circoviruses: a review. Journal of Veterinary Diagnostic Investigation, 12 (1), 3-14.
• Allan, G.M., McNeilly, F., Cassidy, J.P., Reilly, G.A.C., Adair, B., Ellis, W.A. and McNulty, M.S. (1995). Pathogenesis of porcine circovirus; experimental infections of colostrum deprived piglets and examination of pig foetal material. Veterinary microbiology, 44 (1), 49-64.
• MacLachlan, N.J. and Edward J. Dubovi, E. J. (2009). Fenner’s Veterinary Virology, Fourth Edition, 263-265
• Murphy, F.A., Gibbs, E.P.J., Horzinek, M.C., Studdert, M.J. (2001). Veterinary Virology, Third Edition. 357-358
• Quinn, P.J., Markey, B.K., Leonard, F.C., FitzPatrick, E.S., Fanning and S., Hartigan, J. (2011). Veterinary Microbiology and Microbial Disease, Second Edition. 352-355
• Tischer, I., Mields, W., Wolff, D., Vagt, M. and Griem, W. (1986). Studies on epidemiology and pathogenicity of porcine circovirus. Archives of virology, 91(3-4), 271-276.