Buffalopox

Buffalopox

R P KITCHING
Caprine arthritis-encephalitis

Introduction

Buffalopox is an infection of water buffalo (Bubalus bubalis) characterized by the development of vesicles and, subsequently, scabs in the skin of the teats and occasionally other sites, caused by an orthopoxvirus classified as a subspecies of vaccinia virus.1 The buffalopox virus will also infect cattle in which it induces similar lesions, and humans, but has not been reported in African buffalo (Syncerus caffer). Buffalopox has been described in India,1, 3 Bangladesh, Pakistan, Indonesia, Russia and Egypt.2

Aetiology

Comparisons between the DNA of isolates of buffalopox virus from India and vaccinia virus using restriction endonucleases have shown them to be very similar. Water buffalo calves, being readily available, were used in India to produce vaccinia virus for use in humans as a live-virus vaccine against smallpox, by applying it to scarified skin on their flanks. At this site the virus grew to high titres. During the smallpox eradication programme it was not unusual to recover vaccinia virus from cattle and water buffalo in many parts of the world, usually the result of infection contracted from a human vaccinate who usually was concerned with hand-milking domestic or buffalo cows. However, following the successful completion of the eradication programme, the use of calves to produce vaccine and reports of the recovery of vaccinia virus from milking animals ceased. Only from Asia are there continuing reports of the persistence of buffalopox in the milking buffalo population, indicating that the virus has adapted to and survives in this species.3 It has continued to evolve, as shown by small changes in the restriction endonuclease pattern produced by some isolates, and in biological characteristics, such as ceiling growth temperature, as compared to those of vaccinia virus. In humans it produces a lesion similar to milker’s nodules4 on the fingers, interdigital webs, wrist and forearm and may cause systemic symptoms such as fever and enlarged lymph nodes. In a report from India it is suggested that the virus can spread between humans and, in fully susceptible children, produce multiple skin lesions,3 indicating a possible potential as a zoonosis, now that it is no longer used as a vaccine against smallpox. The course of the clinical disease in cattle is less than seven days; this brief duration of the disease is possibly related to previous infection withcowpoxvirus which is also an orthopoxvirus.

Buffalopox virus grows well on chorioallantoic membrane (CAM) of embryonated chicken eggs at 35 °C but, unlike vaccinia virus, not all strains grow at 39,5 °C. The pocks produced on CAM are approximately 3mm in diameter, flat and grey, with a central ulceration. It will also grow in a large variety of cell cultures of different animal origin.

Epidemiology

Little is known of the epidemiology of buffalopox, but it is assumed that the virus is sustained by transmission between milking water buffalo by humans or milking equipment, and to calves by direct contact with their dams or from feeding infected milk. The virus can probably survive in scab material in the damp and cool environment of a cattle shed. In the Indian state of Maharashtra dissemination of the virus has been associated with mixing of buffalo in the large cattle market at Dhulia, and the subsequent movement of infected animals.1, 3

Pathogenesis and clinical signs

Lesions usually occur on the teats of milking buffalo, but may also be present on the perineum, between the hind legs and around the eyes and pinnae of the ears, particularly of suckling calves. There is the typical progression of a poxvirus infection through vesicular, pustular and scab stages over a 14-day period, which may be interrupted by trauma during milking and secondary infection. Mastitis is a frequent complication.

Diagnosis and differential diagnosis

A diagnosis is made on clinical signs, isolation of the virus on CAM or in tissue cell culture and specific neutralization of it with anti-vaccinia virus serum, although the titre may be 40 times lower than against the homologous vaccinia virus. The virus can be identified as a poxvirus by electron microscopy, but it is morphologically indistinguishable from capripoxvirus although different from parapoxvirus. Cowpox virus has not been reported in water buffalo, but it does probably infect this species and, because it is also an orthopoxvirus, is difficult to differentiate. It can be definitively identified only by restriction endonuclease digestion of the purified DNA, using enzymes such as HindIII or PstI. The skin lesions of buffalopox may be confused with those caused by bovine herpesvirus 2 infection, urticaria and insect bites.

Treatment and control

There are no vaccines available against buffalopox, and treatment is supportive to prevent secondary infection or spread to other buffalo or humans. The virus is very susceptible to mild detergents and most disinfectants such as those containing hypochlorite, quaternary ammonium compounds or phenolics.

References

  1. dumbell, k. & richardson, m., 1993. Virological investigations of specimens from buffaloes affected by buffalopox in Maharashtra State, India, between 1985 and 1987. Archives of Virology, 128, 257–267.
  2. fenner, f., wittek, r. & dumbell, k.r. (eds), 1989. Buffalopox. Orthopoxviruses. San Diego: Academic Press Inc. pp. 162–165.

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