The genus Parapoxvirus in the family Poxviridae comprises 4 members: orf virus, BPSV, pseudocowpox virus, and parapoxvirus of red deer in New Zealand.1 Parapoxvirus infections are widespread in ruminants throughout the world and are generally characterized by mild papules and erosions on the muzzle, oral mucosa, and udder. However, mucosal disease, infectious bovine rhinotracheitis, malignant catarrhal fever, and foot-and-mouth disease cause similar lesions in affected cattle.2,3 It is known that PPV can be transmitted to humans by close contact with affected animals or PPV-contaminated materials. The disease in humans is a zoonotic occupational disease for farmers, veterinarians, and abattoir workers.4–8
Parapoxvirus infection is typically diagnosed on the basis of clinical signs, isolation of the virus, and detection of viral antigen or virus particles in lesions during histologic and electron microscopic examinations.9–12 The PCR assays are recognized as fast and sensitive diagnostic methods and have been used widely to detect viruses.13–16 Real-time PCR assays are used routinely for detection of various viral pathogens, whereas real-time amplification techniques are used to quantify viral load in clinical samples.17 A real-time PCR method for detection of PPV has been reported.18–20
Parapoxvirus often induces subclinical infections in herds. There may be numerous subclinically infected animals, and it has been suggested these subclinically affected animals act as a reservoir of infection.21–24 Furthermore, it has been reported that 31 of 45 (68.9%) swab samples obtained from the oral cavity of calves at a livestock market in the United States had positive results for PPV DNA, as determined by use of a real-time PCR assay.25 Although a quantitative PCR assay for estimating PPV viral load has been described for clinically affected cattle,18–20 practical approaches for determining viral load in cattle subclinically infected with PPV remain poorly defined. There is a paucity of information on viral load in cattle subclinically infected with PPV.
We believed that cattle infected with PPV but that did not have clinical signs of PPV infection might be a source for infections on farms. The study reported here was conducted to determine the virologic status of cattle subclinically infected with PPV and the farm environment of those cattle. We compared the PPV DNA load of calves without clinical signs of PPV infection with the DNA load of calves clinically affected with PPV.
Supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan (No. 23380178), and by the Kieikai Research Foundation.
Bovine papular stomatitis virus
Quantitative real-time PCR
Restriction fragment length polymorphism
Men-tip, Japan Cotton Buds Industry Ltd, Tokyo, Japan.
Minisart-plus, Sartorius Stedim Biotech, Goettingen, Germany.
Eagle's MEM Nissui, Nissui, Tokyo, Japan.
QIAamp DNA mini kit, Qiagen, Valencia, Calif.
Premix Ex Taq, Perfect Real Time, Takara Bio, Ōtsu, Japan.
Rox Reference Dye II, Perfect Real Time, Takara Bio, Ōtsu, Japan.
ABI 7500 real-time PCR system, Applied Biosystems, Foster City, Calif.
QIAquick PCR purification kit, Qiagen, Valencia, Calif.
GeneQuant 100, GE Healthcare, Little Chalfont, Buckinghamshire, England.
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