Orf / Vuilbek

‘Orf’ ‘Vuilbek’or ‘scabby mouth’ is an infectious viral disease of the pox virus family. The virus affects goats of all ages but kids are most susceptible. Orf is one of the most important viral diseases because of the economic losses.

The virus is spread by direct and indirect contact and enters through any abrasion in the skin. The virus is very resistant to heat and drying out and so can survive from one kidding season to the next. Ewes can transmit the virus to the kid during parturition. Permanently infected goats can develop, resulting in an endemic situation on the farm. (Picture left: Orf lesions around lips and nose) 

The lesions start as reddish papules which change to yellowish pustules after a few days. By about 11 days they become covered with dark brown scabs. The scabs come off within 2-4 weeks without leaving a scar. When the lesions become severe (cauliflower- like appearance) the goats will show signs of pain, poor appetite (or reluctance to suckle) and lose weight. Ewes with lesions on their udders or teats often will not allow the kids to suckle.

Lesions can develop where there is any damage to the skin and start to appear 2-6 days after the virus is introduced. Abrasions to the lips and muzzle while browsing makes this area the most common site for the lesions to occur. Spread to the gums and inside the mouth and nose can then take place. Bites from midges can be a site of entry for the virus, typically causing lesions on the eyelids, ears and genitals. Suckling kids causing micro trauma to the teats of ewes makes this a potential site for infection and transmission from the kids. Wet conditions can cause softening of the skin around the hooves resulting in abrasions and therefore infection typically between the claws.

In severe cases the spread of the virus becomes more generalised. The generalised form is often fatal with extensive lesions of the mouth, pharynx, oesophagus and even the rumen. Secondary bacterial infection of the lesions can cause mortality which can be greater than 20% depending on the secondary complications. Pneumonia is the most common cause of mortality.Vitamin A deficiency, poor hygiene and stress may predispose animals to severe forms and complications.

Prevention

Vaccination against Orf is available and is recommended, but its limitations should be understood. NB:! DO NOT VACCINATE if you have never had the problem on your farm as you will just be introducing the virus

 If an animal is vaccinate or exposed to a natural infection, further exposure to the virus is still likely to cause disease, but the scabs which form will be less severe and will drop off more quickly (10-14 days instead two to four weeks). This means animals are contagious for a shorter period and will have a knock-on effect in reducing the overall contamination level of the environment and infection level of the herd. Vaccination of already infected animals also helps scabs to fall off quicker.

The best time to vaccinate ewes is 8 weeks before kidding so any lesions which develop in response to the vaccine will have healed before the kid is born. Kids from contaminated ewes can also be vaccinated a couple of days after birth to try and prevent the virus from spreading to other areas of the body. Kids should then be given a second vaccination 8 weeks after the first. Kids from vaccinated ewes will have some immunity via the colostrum, but may become infected, showing fewer clinical signs.

Vaccines are available only from Onderstepoort Biological Products (OBP) at present. The manufacture of vaccine by Grootfontein from farmers’ own virus-rich material has recently been halted  due to legislation. However, this situation is under appeal and will be reviewed.  The vaccine is not administered by injection in the usual manner but by using a thick needle on clean area. Make 2 scrapes about 2.5cm long. The scrapes must be deep enough to make a red mark but not bleed. The vaccine is rubbed into scraped region. A brush can be used for this. It is recommended that this is done in the axilla (armpit) NOT the inner thigh as infection could potentially spread to the udder and genitals.

A lesion develops within 7 days at this site. Always wear gloves as people can get the disease by being infected through abrasions of the skin when treating or vaccinating animals.

(see photo H. De Groot)

Vitamin A supplementation, good hygiene practices, making every effort to manage susceptible animals with as little stress as possible, and minimizing overcrowding will reduce the severity of outbreaks. 

Treatment

No definitive treatment for Orf exists. Treatment is purely supportive i.e. to maintain health in affected animals in the expectation that this will enable them to come through the viral infection without mortality and minimum loss in condition. Blowfly strike is always a risk so must be closely monitored.

Attention should be directed at containing secondary bacterial infection. Crusty or scaly material must be removed in order for antibiotic sprays to penetrate the infected tissues. Vigorous cleaning the lesions which causes then to bleed is thought to stimulate the immune response in the effected animal. Various topical preparations help keep the lesions moist and anti-inflammatory injections can reduce pain in animals which are reluctant to eat. In animals which are badly affected, the use of antibiotics to prevent secondary infections, can be justified. Of the injectable antibiotics, long-acting penicillins seem to be the most effective at controlling secondary bacterial infections. Valuable animals with severe oral lesions can be stomach tubed to be fed.

With the intensification of Angora goat breeding and grazing systems the disease is becoming more prevalent on karoo farms and having greater economic effects.

Dr Mackie Hobson

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