Sheep pox (Qrf) is a pustular inflammation that develops on the skin of sheep after infection with a virus, which can then spread to humans, causing sheep pox in people.

bubble_chart Etiology

This disease is caused by the sheep pox virus, an ether-sensitive DNA virus that primarily affects sheep. Humans become infected through contact with materials contaminated by sick sheep. Therefore, it is more common among shepherds, veterinarians, and slaughterhouse workers. There are currently no reports of human-to-human transmission of the pestilence. Infection confers lifelong immunity, and the virus has been successfully inoculated in humans. Viral growth has been observed in tissue cultures of lesions from both humans and animals.

bubble_chart Clinical Manifestations

The incubation period is 5-6 days. Initially, it presents as small red or purplish-red papules that are firm in texture. These later enlarge into flat-topped blisters, which can develop into hemorrhagic bullae or pustules, sometimes with central umbilication, measuring 3-5 cm in size. Within 24-48 hours, the blisters rupture and become covered with a thick, light brown eschar, surrounded by a distinctive grayish-white or purplish-red halo, which is further encircled by a red halo. The lesion then transforms into a papilloma-like nodule. Eventually, it flattens, dries, forms a scab, and heals spontaneously. The course of the disease typically lasts about 3 weeks but can extend to 5-6 weeks, resulting in permanent immunity. The number of skin lesions is usually limited, appearing as single or a few lesions, predominantly on exposed areas such as the fingers, forearms, and face. Apart from mild local swelling and pain, there are no systemic symptoms or only mild fever, with possible local lymph node enlargement. Some individuals may develop transient maculopapular eruptions on the trunk or erythema multiforme-like rashes on the extensor surfaces of the limbs about 2 weeks after onset.

Histopathology: There is prominent intracellular and intercellular edema within the epidermis, with vacuolization and ballooning degeneration. The dermis shows dense cellular infiltration, primarily composed of histiocytes and macrophages in the center, surrounded by lymphocytes and plasma cells, with rare polymorphonuclear leukocyte infiltration. Throughout the lesion, there are numerous small blood vessels with endothelial cell proliferation and swelling. Eosinophilic inclusions can be observed within the cytoplasm of endothelial cells in the dermal blood vessels.

bubble_chart Diagnosis

Based on contact history, typical rash, and self-healing process, a diagnosis can generally be made. If there is doubt, the scab from the lesion or a biopsy tissue can be examined under an electron microscope. If viral inclusion bodies are found, the diagnosis is certain.

bubble_chart Treatment Measures

1. Avoid contact with sheep and goats infected with sheep pox.

2. Vaccination of lambs aged 2-3 weeks with live sheep pox virus vaccine provides lifelong immunity.

3. Patients generally receive symptomatic treatment.