Ectromelia

Also known as: Mouse Pox

Introduction

Ectromelia is a severe, highly contagious pathogen of mice worldwide. It also affects rats, and the mortaliy rate in both species is very high and can reach 100%. The virus is of the Poxviridae family and causes cell proliferation followed by central necrosis, forming the typical pock lesion. The virus can be carried by tumour cell lines in liquid nitrogen e.g. hybridomas in laboratory mice. Outbreaks in laboratory mouse colonies have often been reported and have caused serious disruptions in biomedical research.

Close contact among mice and rats can spread the virus easily by direct contact. Indirect contact, such as via the fecal-oral route and urine contamination are also common ways of transmission. Newly infected mice may develop pustules in approximately 10 days which often resemble bite marks. Resulting necrosis may lead to the loss of digits and limbs and destruction of liver and lymphoid tissue. Many infected animals, however, may develop latent infections with no clinical symptoms which can be reactivated by stressors such as irradiation and transport.

Clinical Signs

Depending on the severity of the virus there may be very few clinical signs or there may be many signs and the animal may die. In severe cases the characteristic pock like rash will occur over the entire body and the mice will be lethargic, inappetant and depressed. as mentioned above in severe cases, liver failure may occur and limbs and digits may be so severely affected that they fall off. Mice should be culled before any disease reaches such a severe state though.

Diagnosis

Diagnosis of the disease has often been based on its distinctive lesions, but this approach is not reliable because some latently-infected mice and rats may not have symptoms.

Serological detection may indicate prior exposure but cannot confirm the current presence of virus in those latently-infected rodents.

Molecular detection is a rapid, sensitive and specific method to detect and confirm the presence of mousepox virus and this can be done by electron microscopy, PCR or immunofluorescence on faecal pellets, samples of flesh, skin scrapings or blood.

Control

This disease has now largely been eradicated due to the use of specific pathogen free mice and rats worldwide.

References

Blood, D.C. and Studdert, V. P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition), Elsevier Science

Bridger, J and Russell, P (2007) Virology Study Guide, Royal Veterinary College

Paterson, S (2006) Skin Diseases of Exotic Pets, Blackwell Publishing

Roberts, W.A. and Carter, G.A.(1976) Essentials of Veterinary Virology, p. 171, Michigan State University Press, East Lansing, Michigan