Foot rot is a highly contagious and painful hoof disease in small ruminants. It is characterised by inflammatory changes in the hoof area and lameness of the supporting legs. Foot rot is associated with considerable economic damage in sheep farming. The primary causative agent is the gram-negative anaerobic bacterium Dichelobacter nodosus (D. nodosus), which occurs in benign or virulent variants. Only the virulent variant of the bacterium leads to the full symptom spectrum.
Foot rot is highly contagious and thus leads to a particularly rapid spread within the herd. On contaminated pastures, the pathogen spreads to more and more animals through indirect transmission via the soil. Even apparently healthy animals can transmit D. nodosus. Infection can also occur via contaminated transport vehicles or animal drive paths. Apart from the virulence of the pathogenic strains involved, humidity, temperatures above 10 °C, inadequate hoof care, hoof lesions and the secondary infections mentioned above are decisive for the infection and the resulting clinical manifestation. It is possible for the pathogen to spread to uninfected farms. Dichelobacter nodosus has a limited life span of about 14 days on pastures and in the soil. It survives only for a short time in dry environments, so that a risk of infection can be ruled out after only a few days. On moist soils, however, the bacterium can survive up to 42 days, and even up to 6 months under favourable conditions. In hoof horn and in diseased hooves, the pathogen can be detected for up to 3.5 years.
Symptoms
There are different stages of the disease. The extent of the lesions is divided into the grades 1-5 by the definition of the stages of foot rot. In principle, all forms of the disease can occur simultaneously in one foci:
| Grade | Characteristics | Duration |
|---|
| 0 | Claw gap without changes, hairy | |
| 1 | Inflammation of the skin in the claw gap, redness | |
| 2 | Greasy, smelly deposits in the claw gap | 3-4 days |
| 3 | Detachment of bale horn and inner wall | |
| 4 | Expansion to entire sole and outer wall | 7-14 days |
| 5 | Extension to the tip, shoeing out | >21 days |
Definition of the foot rot disease stages according to H. Strobel, 2018.
The initial stages are indistinguishable from simple claw inflammation without involvement of D. nodosus. Beginning with inflammation in the interclaw cleft, dermatitis interdigitalis, there is progressive inflammation and damage to the claw horn. The horn is detached from the claw corium to varying degrees; there is often a foul-smelling, grayish-white greasy mass in the claw gap as a product of pus production. Severe cases are characterized by sole perforations and shoeing.
Typical symptoms are lameness and feeding while kneeling on the fore extremities to relieve the painful claws. Affected animals lie down more, as a result there is reduced feed intake, emaciation, wool damage and performance depression.
Therapy
Foot rot is a painful disease and must be treated with regard to animal welfare. Measures are necessary both when benign infection and virulent infection of D. nodosus are detected, as acute pain associated with reduced performance also occurs in the benign form. With regard to therapy, decisive changes have occurred, among other things, due to the new approval of drugs.
- Separation of healthy and diseased animals
- Surgical treatments such as the complete removal of the affected altered hoof horn and the purulent mass by cutting are problematic due to the lengthy recovery process and the painfulness. In principle, bleeding injuries should be avoided during hoof trimming. Bandaging should be changed daily because of the ideal warm, moist, anaerobic microclimate (promotes bacterial growth!). Safe disposal of necrotic waste after surgical treatments is necessary due to the risk of infection from waste contaminated with bacteria!
- Treatment of the affected hooves with antiseptic wound spray and/or hoof baths (e.g. with zinc sulphate).
- General antibiotic treatment of severely diseased animals
- Follow-up control and treatment at regular intervals until cured
- Vaccination works both prophylactically and therapeutically. Vaccination alone is not sufficient for herd rehabilitation.
Foot rot is a herd disease. The exclusive treatment of individual animals is not sufficient. In order to achieve herd rehabilitation, the following criteria must be met:
- All animals must be included in the treatment
- All acute hoof infections must be treated within the first few days
- All treated animals must be followed up until completely cured
- All healthy animals must be protected as soon as acute cases occur
In individual animals, there should be an improvement in lameness symptoms within a few days after treatment. Complete healing usually takes as much time as the course of the disease before therapy.
Within the herd, it is necessary to examine and treat all animals at the same time: Infected animals are systematically treated with antibiotics; healthy animals are protected by precautionary measures (hoof baths).
It is possible to observe the further course of the disease in the herd by using different colour markings and/or local separation of healthy and diseased animals. Regular herd treatments can lead to freedom from the disease if the number of latently infected animals can be continuously reduced over a period of years. After recovery, animals must be moved to pasture that has not been used for at least six months to prevent reinfection of irritated hooves. However, if animals in a herd are in contact with the wild animal population, this is difficult to achieve.
AGES - Austrian Agency for Health and Food Safety
