Special Topics on Swine Diseases: Porcine Circovirus Disease

Pathogen:
Porcine circovirus (PCV) is the smallest known animal virus, classified into two serotypes: PCV1 and PCV2. PCV1 is non-pathogenic, while PCV2 is pathogenic and the primary causative agent of Post-weaning Multisystemic Wasting Syndrome (PMWS). However, PMWS often involves co-infections with other pathogens like PPV, PRRSV, and PRV. PCV2 is also associated with Porcine Dermatitis and Nephropathy Syndrome (PDNS), reproductive disorders in sows, enteritis, pneumonia, and congenital tremor in piglets.

Epidemiology:
PMWS, the first recognized disease caused by PCV2, primarily affects pigs aged 5–16 weeks, with the highest incidence in 6–8-week-old pigs and rarely in suckling pigs. Symptoms often appear 2–7 days post-weaning. Acute outbreaks can have a mortality rate of up to 10%, with stunted growth in survivors. Mortality rates may exceed 25% due to secondary infections.

PCV2 is highly contagious, spreading through nasal discharge, feces, and oral or respiratory routes. Pregnant sows can transmit the virus vertically to piglets via the placenta. Experimental infection shows 100% transmission among cohabiting pigs, confirming horizontal spread. The virus also spreads via contaminated clothing, equipment, and semen.

Clinical Symptoms:

1. Post-weaning Multisystemic Wasting Syndrome (PMWS):
   • Common in pigs aged 5–12 weeks.
   • Morbidity: 5–30%; mortality: 5–40%.
   • Slow disease progression lasting 12–18 months.
   • Symptoms include progressive respiratory distress, weakness, emaciation, weight loss, stunted growth, jaundice, anemia, diarrhea, swollen lymph nodes, and high mortality. Survivors often remain stunted.
2. Porcine Dermatitis and Nephropathy Syndrome (PDNS):
   • Occurs in pigs aged 8–18 weeks, with a morbidity of 0.15–2% (up to 7% in severe cases).
   • Symptoms include red or purple spots, merging into bands or patches on the hindquarters, limbs, and abdomen, eventually spreading to the back and ears.
   • Mild cases recover spontaneously, while severe cases may present fever, reduced appetite, lameness, edema, and death within days or weeks.
3. PCV2-Associated Interstitial Pneumonia:
   • Common in nursery and finishing pigs aged 6–14 weeks.
   • Morbidity: 2–30%; mortality: 2–10%.
   • Lungs appear diffusely collapsed, rubbery, and mottled gray-red or gray-brown.
4. PCV2-Associated Reproductive Disorders:
   • Includes increased return-to-estrus rates, abortions, stillbirths, mummified fetuses, and weak piglets.
5. PCV2-Associated Congenital Tremor (CT):
   • Tremors in piglets after birth, linked to PCV2.
   • Increased neonatal mortality.

Post-Mortem Lesions:
Affected pigs exhibit emaciation, anemia, pale skin, jaundice (20% of suspected PMWS cases), enlarged lymph nodes (3–4 times normal size), rubbery lungs with gray-brown inflammation, darkened livers with interlobular fibrosis, edematous kidneys (up to 5 times normal size) with necrotic foci, and mild splenic enlargement. The pancreas, small intestine, and colon often show enlargement and necrosis.

Histopathological Changes:
Widespread lesions include multifocal or diffuse interstitial pneumonia in lungs, hepatocyte necrosis in livers, multifocal interstitial nephritis in kidneys, myocarditis in hearts, and granulomatous inflammation in lymph nodes, spleen, tonsils, and thymus. Lymphocyte depletion is a hallmark of PMWS.

Prevention and Treatment:

1. Use antibiotics like tilmicosin, tylosin, florfenicol, cephalosporins, or sulfonamides to reduce secondary infections. Support kidney function with diuretics and renal recovery agents.
2. Administer astragalus polysaccharide injection and vitamin B1, B12, and C via intramuscular injection, or provide supplements like Javita or Amino-Gold in water or feed.
3. Use antiviral agents such as interferons, leukocyte-derived cytokines, immunoglobulins, or transfer factors, combined with plant-based antiviral extracts for improved outcomes.
4. Regular disinfection with Roxycideto eliminate pathogens, prevent viral spread, and maintain biosecurity.