Contagious Footrot

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Also known as: Scald — Footrot — Strip

Introduction

An economically important disease causing lameness in sheep, is associated with under-running of the hoof and a characteristic 'odour'. Footrot is caused by Dichelobacter nodosus together with Fusobacterium necrophorum.

The first stage of the disease (scald) involves moisture and trauma allowing F. necrophorum to enter. If D. nodosus is not present, the superficial damage can heal without any signs of lameness. However, the damage F. necrophorum causes aids bacterial penetration of the epidermis by D. nodosus resulting in necrosis and inflammation and sloughing of the hoof horn (footrot).

Carrier animals are a major source of infection and are difficult to find as they are often sub clinical cases.

Recovery occurs but animals are not immune following an initial infection.

Signalment

Affects sheep, particularly those kept in wet, warm conditions.

Diagnosis

Can be made on a history of lameness and rapid spread amongst the flock in combination with clinical signs. Under-running of horn in combination with separation of the horn on multiple feet of the same animal is characteristic of footrot.

Early cases only affecting the interdigital space may be mistaken for ovine interdital dermatitis and more severe cases may be confused with a foot abscess.

It is possible to identify D.nodosus microscopically via stained smears from the affected foot however many other bacteria will also be present.

Clinical Signs

Lameness is often the first clinical sign to be noted and can vary in severity. In the worst cases sheep become recumbent or on their knees. If rams are affected they may not be able to serve and if ewes are affected they may not be able to take the weight of a ram. Under-running of the horn is present and there is often a necrotic discharge which causes the characteristic foul 'odour'.

Pathology

Grossly: Early lesions are red, moist, swollen and interdigital skin is eroded. This spreads to epidermal matrix of the hoof leading to separation of the horn and a malodorous exudate. Regeneration is attempted as germinal epithelium is not destroyed. Chronic infections can result in a long misshapen hoof. Benign footrot results in only the interdigital skin being affected and a slight separation of heel horn. Mostly this is the type occuring in cattle.

Treatment

A single dose of antibiotics ideally penicillin or oxytetracycline gives rapid resolution for individual animals.

Foot-bathing is also useful zinc sulphate and formalin can be used. There should be a dry area where the sheep can stand post dip to give the chemical time to take affect. This is more useful as a form of control to prevent footrot.

Vaccination is a further form of control. This only gives 12 weeks of protection and hence must be instigated at high risk periods. Two doses are required four weeks apart.

Another way to control disease is to cull repeatedly affected animals and hence carriers of the disease.


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Contagious Footrot in sheep publications since 2000


References

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

http://www.footrotinsheep.org/




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