Circovirus infection
Subperitoneal bleeding
PCVAD is becoming of considerable concern in modern pig production especially in Canada, the US and Europe.
Porcine Circovirus Associated Disease (PCVAD)
Porcine Circovirus Associated Disease (PCVAD) causes wasting and mortality in piglets from 6 weeks of age onwards. Clinical disease was first described in Western Canada in 1991. The syndrome is becoming of considerable concern in modern pig production especially in Canada, the US and Europe.
PCVAD is a multifactorial disease. Porcine circovirus type II (PCV-2) plays a major role, but management factors and other disease agents are also relevant.
Etiology of PCVAD
Porcine circovirus (PCV) is associated with PCVAD. It is a small, resistant, ring
shaped single-stranded DNA virus.
Two serotypes have been isolated:
- Type 1 causes no known disease.
- Type 2 can be found in the lesions and can be isolated in pure culture in piglets showing PCVAD signs
There are several different strains (biotypes and genotypes).
Experimentally, colostrum deprived piglets inoculated with PCV-2 develop typical PCVAD lesions. They are however more likely to develop lesions if inoculated simultaneously with another virus, such as porcine parvovirus (PPV) or porcine reproductive and respiratory syndrome virus (PRRSV).
Serum surveys in Europe and North America have shown that PCV-2 infection is widespread throughout the pig population but only a small proportion of seropositve herds have a history of clinical disease. It is not known why some infections result in disease while others are subclinical.
Environmental factors, such as drafts, overcrowding, poor air quality, co-mingling of age groups or other stressors exacerbate the severity of the disease.
Clinical signs
PCVAD is a slow and progressive disease with a high fatality rate in affected pigs. It affects weaned
pigs.
Signs are usually seen from about 6 - 8 weeks of age:
- Weaned pigs lose weight and gradually become emaciated
- Rough haircoat
- Pale sometimes jaundiced skin
- Sudden death
- Enlarged peripheral lymph nodes – inguinal lymph nodes are often very prominent
- May show diarrhea
- May show respiratory distress caused by interstitial pneumonia
- Rarely incoordination.
Piglets affected by Porcine Circovirus Associated Disease (PCVAD)
Post weaning mortality is likely to rise to 6 - 10% but is sometimes much higher. Mortality peaks in affected piglets around 9 weeks of age.
Clinical cases may keep occurring in a herd over many months. They usually reach a peak after 6 - 12 months and then gradually decline.
Diagnosis
Most pig herds will be serologically positive for PCV so serology is of little value.
The clinical syndrome (stunting, pallor, dyspnoea, jaundice, diarrhoea and mortality) suggests
PCVAD, but confirmation is based on the pathological findings and demonstration of the virus in
tissues. As post mortem lesions are variable it is often necessary to post mortem several pigs.
Macroscopic lesions
- Emaciated pale or jaundiced carcass
- Very enlarged lymph nodes and spleen. The lymph nodes are white on cut surface
- Swollen kidneys, white spots may be visible on the cut surface
- Rubbery mottled lungs
- Intestinal tract - Changes in the stomach include ulcers in the pars oesophagea. There may be oedema around the pancreas, the small intestine is thin-walled, the contents watery and the caecum distended and there is reddening of the caecal wall
Oedematous kidney with white spots visible on the cut surface
Haemorrhages in the gastric mucosa
Microscopic lesions
Diagnosis is based upon the presence of PCV type 2 histological lesions in affected organs.
Immunohistochemistry is used to demonstrate PCV in tissues. Microscopically these lesions
are characteristic and diagnostic particularly if the circovirus is demonstrated in them.
Treatment
Apart from support therapy, nursing and antimicrobials to control secondary
bacterial infections, there is no specific treatment for PCVAD. With nursing
some animals may recover. This is not possible on any large scale
and high mortality often persists under farm conditions.
- All in all-out systems are essential for control
- PCV is a very resistant virus and effective disinfectants must be used.
- Good management of environmental factors – ventilation, temperature and humidity.
- Avoid high stocking density and reduce mixing of pigs.
- Early recognition of sick pigs and segregation is essential.
- Keep similar age groups of pigs segregated to separate buildings or sections and reduce faecal transfers as far as possible.
- Use solid partitions between pens.
- Vaccinate for parvovirus (PPV) and control PRRS.
- Only purchase breeding stock from herds with no history of the disease or close the herd and use AI only.
- Only use semen from AI studs where all the boar sources have no history of disease.
- Pay particular attention to the possibility of faecal transmission via equipment, boots and vehicles.
- Vaccines are available to assist with the control of PCVAD.