Transmission of ovine herpesvirus 2 from asymptomatic boars to sows.
|Article Type:||Letter to the editor|
Herpes (Care and treatment)
Herpesvirus diseases (Diagnosis)
Herpesvirus diseases (Care and treatment)
Disease transmission (Research)
Swine (Care and treatment)
Costa, Erica Azevedo
Viott, Aline de Marco
Machado, Glauber de Souza
Bomfim, Maria Rosa Quaresma
Coelho, Fabiana Magalhaes
Lobato, Zelia Ines Portela
Guedes, Roberto Mauricio Carvalho
|Publication:||Name: Emerging Infectious Diseases Publisher: U.S. National Center for Infectious Diseases Audience: Academic; Professional Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2010 U.S. National Center for Infectious Diseases ISSN: 1080-6040|
|Issue:||Date: Dec, 2010 Source Volume: 16 Source Issue: 12|
|Topic:||Event Code: 310 Science & research|
|Geographic:||Geographic Scope: Brazil Geographic Code: 3BRAZ Brazil|
To the Editor: Malignant catarrhal fever (MCF) is an often lethal
viral disease of susceptible biungulates from the Bovidae, Cervidae, and
Suidae subfamilies. MCF in pigs has been associated with direct or
indirect contact with sheep, which are the main reservoir of ovine
herpesvirus 2 (OvHV-2) (1). A recent report detected infected but
asymptomatic swine in the absence of known exposure to sheep or goats
(2). Porcine MCF is difficult to diagnose because of its nonspecific
clinical signs and sporadic nature; however, an outbreak involving 41
swine has been described (3). Pigs are terminal hosts and are not
believed to spread the virus. Here we describe OvHV-2 DNA in the blood
and semen of asymptomatic boars and from the brain of symptomatic sows
and gilts with MCF that was probably transmitted by artificial
The MCF cases occurred on two 3-site commercial farms with 2,700 and 1,670 sows in 2 different counties in southwestern Brazil. No MCF losses previously had been recorded in the region, and the animals had no known direct or indirect contact with sheep. The 2 farms had high biosecurity. The first case was recorded in September 2004, and the number of cases increased in July 2006. Twenty-eight sows and gilts, 20 of them pregnant and at [greater than or equal to] 25 days' gestation, died during January 2007-March 2008, when the last case was observed.
Clinical features in sows and gilts were depression followed by abortion, fever (41[degrees]C), and anorexia. After the onset of clinical signs, neurologic symptoms developed such as ataxia, tremors, convulsions, and aggressive behavior. Animals that survived longer showed forelimb paralysis, stood in a dog-sit position, and gnawed with abundant salivation on pen bars.
Specimens from randomly selected dead sows and gilts from the outbreaks during 2004-2008 were obtained for histopathologic examination, immunofluorescence testing for rabies virus, viral and bacterial isolation, and PCR. No bacterial or viral growth was detected, and direct immunofluorescence for rabies virus was negative. Microscopic examination showed high-grade nonpurulent meningoencephalitis characterized by lymphocytic cuffings with vasculitis in the brain hemisphere, the brainstem, the spinal cord, and, to a lesser extent, the cerebellum. Multifocal areas of edema, fibrinoid necrosis, and lymphocytic infiltration also were observed (Figure). OvHV-2 DNA was detected by using a specific PCR (4) in 5 of 7 paraffinized sections of the brainstem (5). To analyze the possible presence of other porcine lymphotropic herpesviruses in samples that reacted positively for OvHV-2, a nested PCR with degenerate primers (6,7) was applied. None of the OvHV-2-positive samples reacted positively for porcine lymphotropic herpesviruses. To confirm that the virus was a member of the MCFV group, we purified 1 amplicon and submitted it for automated sequencing. This nucleotide sequence was deposited in GenBank under accession no. HQ223415, and it showed 99% identity with previously deposited OvHV-2 sequences.
To find possible carriers of the virus, blood samples were collected from 9 pregnant sows, 10 nonpregnant sows, and 30 breeding boars and analyzed for OvHV-2 DNA. Samples from 3 boars were positive. Nasal swabs and semen samples were collected from these infected boars to investigate the potential mode of OvHV-2 transmission, and OvHV-2 DNA was detected only in semen samples. Two of the 3 semen samples had >350 copies/2 [micro]g of total DNA, suggesting that these animals shed virus (8,9). During this period, all infected boars remained clinically healthy.
In Brazil, porcine MCF has been found primarily in pregnant sows and gilts. Our findings of OvHV-2 DNA in the semen of asymptomatic boars suggest that the OvHV-2 in the sows and gilts originated from asymptomatic boars that were responsible for maintaining the virus in the herd. Whether virus shedding in the semen was temporary or lasted for a long period is not known.
Emergence of OvHV-2 in boars that had no known contact with sheep was surprising, especially given the possibility of venereal transmission through contaminated semen. The occurrence of OvHV-2 infection in other specific pathogen-free farms is unknown, and it is not possible to suggest a strategy to guarantee OvHV-2-free herds.
Financial support was provided by Fundacao de Amparo a Pesquisa do Estado de Minas Gerais, Conselho Nacional de Desenvolvimento Cientlfico e Tecnologico, and Coordenacao de Aperfeicoamento de Pessoal de Nlvel Superior.
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Erica Azevedo Costa, Aline de Marco Viott, Glauber de Souza Machado, Maria Rosa Quaresma Bomfim, Fabiana Magalhaes Coelho, Zelia Ines Portela Lobato, Mauricio Resende, and Roberto Mauricio Carvalho Guedes
Author affiliations: Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil (E. Azevedo Costa, G. de Souza Machado, M.R. Quaresma Bomfim, F. Magalhaes Coelho, Z.I. Portela Lobato, M. Resende, R.M. Carvalho Guedes); and Universidade Federal do Parana, Palotina, Parana, Brazil (A. de Marco Viott)
Address for correspondence: Roberto Mauricio Carvalho Guedes, Departamento de Cllnica e Cirurgia Veterinarias, Escola de Veterinaria, Universidade Federal de Minas Gerais, Av. Antonio Carlos, 6627, Bairro Pampulha, CEP 31270-901, Belo Horizonte, MG, Brazil; email: email@example.com
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