GENERAL INTRODUCTION: POXVIRIDAE

Introduction

Buffalopox is an infection of water buffalo (Bubalus bubalis) characterized by the development of vesicles and, subsequently, scabs on the skin of the teats and occasionally other sites.⁴ 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). It has been described in India,^{4, 8} Bangladesh, Pakistan, Indonesia, Russia and Egypt.⁵

Aetiology and epidemiology

Buffalopox virus belongs to the genus Orthopoxvirus and family Poxviridae (see General Introduction: Poxviridae). Its genome is 195 360 base pairs in length and contains 177 protein-coding sequences.¹ Comparisons between the DNA of isolates of buffalopox virus from India and vaccinia virus using restriction endonucleases and  phylogenetic analysis showed that they are very similar.¹

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 was involved 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  milking buffalo populations, indicating that the virus has adapted to and survives in this species.⁸ 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 nodules⁹ 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,⁸ indicating the potential as a zoonosis, now that it is no longer used as a vaccine against smallpox. Human to human transmission of buffalopox virus was demonstrated in 2004-2005  in Karachi, Pakistan involving at least 19 patients as well as a medical staff member who developed lesions on his fingers. The diseased patients recovered in three to four weeks.¹⁶ A laboratory- acquired infection of buffalopox virus in India has also been reported.¹⁰

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

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  sheds. 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.^{4, 8} Decreased immunity to orthopox virus is possibly playing a role in increased  prevalences of buffalopox in both water buffalo and humans in western Maharashtra.⁷

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 (see General Introduction: Poxviridae) over a 14-day period, which may be interrupted by trauma during milking and secondary infections.¹⁴ In diseased cows the milk yield is reduced and mastitis is a frequent complication.¹²

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 with cowpoxvirus, which is also an orthopoxvirus.¹⁵

Diagnosis and differential diagnosis

Scabs or swabs collected from skin lesions are preferred to confirm the diagnosis by detection of the virus  by transmission electron microscopy (TEM), virus isolation, molecular methods or immunohistochemistry.⁶ The virus can be identified as a poxvirus by TEM, but it is morphologically indistinguishable from capripox and other orthopox viruses, although it can be differentiated from parapoxvirus (see General Introduction: Poxviridae).

Although infections with cowpox and vaccinia viruses have not been reported in water buffalo they are likely...