Footrot

Sheep and Goats: Footrot is a contagious bacterial infection of sheep and goats caused by Dichelobacter nodosus, often in association with other bacteria. Initial infection involves the skin between the claws and may extend to cause separation of the horny hoof from the underlying soft tissue (corium). Footrot may be classified as benign, intermediate or virulent depending on the mix of bacteria involved, their virulence and the amount and location of tissue damage. In benign footrot, dermatitis (scalding) is confined to the interdigital skin and cannot be distinguished clinically from interdigital dermatitis. In virulent footrot, if conditions are suitable, the infection extends to under-run and detach the hoof. In sheep, the term footrot is usually only used to describe virulent footrot. 

Note that in goats the clinical signs are not necessarily indicative of whether the bacteria are benign or virulent, unlike in sheep. 

New infection can only establish in conditions that provide moisture and microtrauma to macerate the interdigital skin. Cases are more common in warm wet conditions. 

Symptoms are more severe in Merino than British breed sheep. Goats vary in susceptibility. 

Infection can persist for months in small pockets in the foot. Cases of mild or sub-clinical infection may slip through on-farm screening and enter assembly points. If prolonged wet conditions underfoot are then encountered at any point in the export process, the disease may flare up and outbreaks of lameness will occur. 

Virulent footrot is a notifiable disease in some Australian states and is subject to control and eradication programs. 

Cattle: Footrot in cattle is a painful bacterial cellulitis of the foot extending from the interdigital cleft, associated with infection with Fusobacterium necrophorum and other bacteria. Wet, boggy conditions macerate interdigital skin allowing entry of bacteria. Interdigital trauma from foreign bodies such as stones or straw also predisposes the area to infection. Footrot usually occurs sporadically but sometimes outbreaks are seen in poorly drained, muddy conditions. Suitable boggy conditions exist in assembly depots after rain. Occurrence is rare at sea despite pen floors being deep in slurry. This may be because gravel or other sharp material is not present to traumatise interdigital skin. 

Dichelobacter nodosus infection can occur in cattle with foot lesions but in all cases investigated to date, it has been associated with strains of the organism that are benign in sheep.

Clinical diagnosis should be sufficient for diagnosis. If laboratory confirmation is required, submit smears and swabs of interdigital exudate and necrotic tissue from multiple animals for bacteriology. 

Differential diagnoses include foot abscess (typically restricted to one foot), toe abscess and founder (laminitis) resulting from an excessively carbohydrate-rich diet. 

In cattle, footrot will present as sudden lameness in one or more animals, and one or more feet, with swelling of the interdigital space and coronet. Close examination of the foot will reveal a foul smelling, necrotic ulcer occupying the interdigital cleft. 

If left untreated, the infection may spread to the interphalangeal joints and deeper structures of the foot, causing severe and chronic lameness. Differential diagnoses include a foreign body stuck between the claws, and solar abscess or other septic inflammatory process affecting the claw.

Systemic administration of antibiotics (procaine penicillin or oxytetracycline) and dry underfoot conditions usually resolve even severe lameness after a few days without the need to pare away dead horn. If antibiotics are injected, topical application of aerosol sprays of cetrimide or oxytetracycline is unnecessary. 

Benign footrot may resolve if underfoot conditions are kept dry. Lameness in intermediate footrot may resolve just with paring to expose the affected area. 

Foot bathing in formalin or zinc sulphate (with surfactant) is an option. However, the cost, chemical hazards and unpredictable results mean that injectable antibiotics are likely to be preferred. Affected cattle should be examined as part of the initial workup to confirm the diagnosis and any foreign bodies removed from the interdigital cleft.

Topical treatment and bandaging are unnecessary. Instead, treat with systemic antibiotics (procaine penicillin, florfenicol, or oxytetracycline) for three to five days. If treated early, recovery is usually rapid. If lameness does not resolve in a few days, check for extension of infection into deeper structures, interdigital foreign body, a solar abscess, or other lesion. In severe cases where joint or other deep structures of one claw are affected, amputation of the claw may be required. Note that this procedure may require prolonged time for recovery.

Spelling contaminated areas for two weeks removes Dichelobacter organisms from soil, mud or pasture. There is a short-acting vaccine for footrot in sheep, however it does not cover all strains of D. nodosus. In addition, it needs to be used in conjunction with other control strategies, and reaction to the vaccine is common, often resulting in granulomas or abscesses.