Porcine Respiratory and Reproductive Diseases
Lalrinkima, S. Hemalatha
Department of Veterinary Pathology,
Madras Veterinary College, Chennai
Introduction
A syndrome of reproductive failure and respiratory disease of unknown etiology was originally discovered in swine herds in North Carolina, Iowa and Minnesota in 1987 and 1988. In 1991, Wensvoort and his co-worker and White reported a similar kind of syndrome in Germany, Netherlands, England, Belgium and Spain. Anorexia, late term abortions (days 107-112), higher numbers of stillborn, mummified and debilitated piglets, delayed return to estrus and increased preweaning mortality were the sign of reproductive type of the disease in the United States. Pronounced hyperpnoea, fever and interstitial pneumonitis in young pigs and mild flu like signs were seen in nursing, growing and finishing pigs. The diseases is also known as mystery swine diseases, blue ear, porcine epidemic abortion and respiratory syndrome (PEARS).
India reported the first outbreak of PRRS in the pig population of Mizoram state to the Office International des Epizooties in 2013 by Rajkhowa and his co-worker. The Indian state of Mizoram shares a 510-kilometer porous international border with Myanmar. Hundreds of pigs cross the international border illegally into Mizoram on a regular basis not only for slaughtering but also for breeding purpose. In Myanmar, highly pathogenic PRRS was discovered for the first time in 2011 and the illegal trade of pigs through the porous international border with Myanmar was the main route of entry for HP-PRRSV in Mizoram.
Etiology
PRRSV is an enveloped, single stranded positive sense RNA virus belonging to the family Arteriviridae within the order Nidovirales.
Transmission
Pigs could become infected through direct contact or indirect contact with fomites. PRRSV was transmitted by the respiratory, oral, mucosal and percutaneous pathways. Aerial transmission (short or long distance), coitus or insemination, ingestion, contact and injection (most often iatrogenically) were among the other sources of transmission. Vertical transmission was important during the last trimester of gestation.
Symptoms
Clinical signs include anorexia, pyrexia, agalactia, lethargy and sometimes skin discoloration. Respiratory signs include labored breathing and coughing. Blue (cyanosed) ears, blue vulvas, blue skin patches and erythematous plaques were among the skin abnormalities seen in sows and piglets. The discoloration appeared to be most common after 5-7 days of clinical manifestation. Reproductive losses were a characteristic feature of the disease in pregnant sows and might continue for 4-5 months occupying an entire reproductive cycle within a herd. Abortions might occur from as early as 22 days post mating to 109 days although premature and late farrowing were much more common. In weaning, splay legs were common and many piglets died in their first week.
Blue ear in pigs affected with PRRS Abortion in pig
Pathological findings
Gross pathological lesions of affected lungs were slightly firm, diffusely red tan, non-collapsing, mottled gray to tan and moist. There is enlargement of the lymph nodes. PRRSV infected litters contained variable numbers of normal pigs, small weak piglets and dead pigs that were either fresh stillborn, autolytic stillborn or mummified fetuses. Gross fetal lesions included ascites, hydrothorax and hydroperitoneum. Microscopically, lung revealed interstitial pneumonia with thickening of alveolar septate by macrophages and a few lymphocytes.
Interstitial pneumonia in pigs characterized by heavy and non-collapsing lungs with rubbery texture
Diagnosis
A diagnosis of PRRS virus infection was suggested by clinical signs, respiratory and reproductive problems in breeding stock. Detection of the antigen by isolation of the virus and detection of the antibodies by ELISA, Immunoperoxidase monolayer assay (IPMA), indirect fluorescent antibody (IFA) test and serum virus neutralization (SVN) tests. Tests based on polymerase chain reaction (PCR) had been developed for detecting PRRS virus RNA in clinical samples.
Differential diagnosis
Differential diagnosis of PRRS include leptospirosis, pseudorabies, swine influenza and viral respiratory and reproductive diseases like PCV-2, classical swine fever and porcine parvovirus. Bacterial diseases like Mycoplasma hyopneumoniae, Actinobacillus pleuropneumonia.
References
Rajkhowa, T.K., G. Jagan Mohanarao, A. Gogoi, L. Hauhnar and L. Isaac. 2015. Porcine reproductive and respiratory syndrome virus (PRRSV) from the first outbreak of India shows close relationship with the highly pathogenic variant of China. Vet. Q. 35(4): 186–193.
White, M.E.C. 1992. The clinical signs and symptoms of ‘blue-eared pig disease’ (PRRS). Vet. J. 28: 62-8.
White, M. 1991. Blue ear disease of pigs. Vet. Rec. 128: 574.
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