Bovine Alphaherpesvirus 2
Also known as
BoHV2, Allerton virus infection, Bovine herpesvirus 2, Bovine herpesvirus type 2, Bovine mammillitis virus, bovine ulcerative mammillitis virus
Bovine alphaherpesvirus 2 (BoHV2) is a virus (of the family Herpesviridae) that causes two different diseases in cattle: bovine mammillitis (infection of the skin and teats of cows’ udders, primarily in dairy cattle) and pseudo-lumpy skin disease.
Pseudo-lumpy skin disease was first seen in South Africa where a similar but more serious disease called lumpy skin disease (caused by a poxvirus), is also prevalent. Pseudo-lumpy skin disease occurs primarily in southern Africa, but is also occasionally seen in the U.S., Australia, and the UK.
Pseudo-lumpy skin disease has an incubation period of 5 to 9 days and is characterized by mild fever, followed in a few days by sudden appearance of skin nodules that are circular or oval-shaped. There may be only a few, or many nodules--on the face, neck, back, and perineum of the infected animal.
The nodules are hard and firm, about ½ to ¾ inch in diameter upon first appearance, then enlarging to about 1 to 2 inch diameter. They sometimes are on a small stalk, but have a flat surface with a slightly depressed center, and involve only the superficial layers of the skin. These nodules tend to weep and ooze, and form brown crusts.
The skin beneath the crusts dies. Within 7 or 8 days, the local swelling subsides and the skin heals without any scarring; the crusts fall off, to reveal new skin underneath, and healing is complete within a few weeks. New hair grows back within a couple months.
Bovine mammillitis is characterized by lesions on just the teats and udder. The virus is probably transmitted to the udder area by an arthropod vector (such as biting flies), but has also been thought to be spread by people milking the cows, and milking machines. Indirect transmission may occur via contaminated utensils and semen. Incubation period is 5 to 10 days before the skin lesions appear.
These lesions may be aggravated by low skin temperature (such as in swollen or hairless areas) causing reduced blood circulation.
Bovine ulcerative mammillitis is often associated with cold weather and tends to occur most often in early winter and in first lactation heifers. Young cattle are more susceptible.
Mammillitis may appear sporadically in a few individual animals or in outbreaks with multiple cows in the group affected, sometimes up to 30% of the milking herd.
- Lesions on teats and udders
- Reddish blisters that may run together and ooze
- Skin nodules
- Extensive weeping
- Sloughing of skin
BoHV2 is similar in structure to the human herpes simplex virus.
In many countries, bovine herpesvirus 2 is recognized only as a cause of mammillitis, but this virus can also cause generalized skin disease including pseudo-lumpy skin disease. Lesions usually occur only on the teats, but in severe cases most of the skin of the udder may be affected.
Occasionally, heifers may develop fever, coinciding with the appearance of lesions. Milk yield may be reduced by as much as 10% due to difficulty in milking the affected cows, and concurrent mastitis.
Pseudo-lumpy skin disease (Allerton virus) occurs most commonly in southern Africa, in moist low-lying areas, especially along rivers, and with highest incidence in summer and early fall. Susceptible cattle don’t seem to become infected by placing them in contact with diseased cattle--if they are all housed in insect-proof facilities.
It is therefore assumed that mechanical transmission of the virus occurs via insects such as biting flies, but the specific vector is still unknown. Buffalo, giraffe, and other African wildlife may be naturally infected.
Although milking machines were initially believed to be responsible for transmission of mammillitis in dairy herds, there is evidence that this is rarely the case. The infection may spread rapidly through a herd, but in some outbreaks the disease is confined to newly calved heifers or pregnant cattle in late gestation.
Diagnosis depends on clinical appearance and finding the virus in skin scrapings or biopsy.
Pseudo-lumpy skin disease causes generalized superficial skin lesions over the body and is less common than mammillitis. The difference in clinical manifestations between the two diseases may be due to the strain of the virus or the method of infection.
Control of biting flies is helpful, but often difficult. In dairy herds, recommendations are to milk affected cows last, and use udder wash and teat disinfection to reduce spread of infection.
Disinfect milking machine and hands between cows and after milking. Check affected udders regularly to make sure skin damage does not proceed to mastitis.
Treatment is aimed at medicating the skin and reducing the spread of infection to other animals. Teat dips with iodine-based solution or crystal violet lotion are often used.
Ointment and udder cream applied before milking can soften the scabs and speed healing of skin.