Herpesvirus I causes an invariably fatal disease in cattle transmitted by sheep and wildebeest (predominantly the blue wildebeest).
Most free-living adult wildebeest are persistently infected but only excrete the virus under conditions of severe stress.
Blue wildebeest calves contract the virus either in the uterus or shortly after birth. Up to 4 months of age they secrete large amounts of virus in their nasal and ocular secretions and form an important role in disease transmission. Older calves also secrete virus but not in such high numbers.
The natural calving of wildebeest makes the predictability of the disease occurrence easier. In South Africa peaks occur from January to May and from September to November. Generally it is assumed that close contact is needed for transmission to cattle but wind can carry the virus for up to several hundred meters. It is possible that a vector may be involved especially where the disease is transmitted over a distance.
The sheep form of snotsiekte is spread in a similar fashion to the above but the occurrence is lower than that of the wildebeest type.
The time lapse from the time of infection to the time the first symptoms are seen is usually 3 – 7 weeks but may be as long as 6 months.
Fever, typical bilateral nasal discharge which eventually becomes purulent (pussy) and thick. The nose becomes inflamed and erosions occur; the longer the disease, the worse the symptoms. Typically the eyes develop a thick discharge and the cornea becomes develops an opaque white colour.
Other symptoms also occasionally occur. Once clinical signs set in animals usually die within a few days but it may take up to 21 days to die. Mortality rates are high although occurrence is usually sporadic rather than epidemic. High stress and transporting infected cattle during their incubation period can cause ‘mini-outbreaks’ in so-called clean areas.
A diagnosis is made from the history, clinical signs, post mortem and blood tests. Blood tests can distinguish between the wildebeest and sheep varieties. There are other diseases with similar symptoms that can confuse the picture. It is, therefore, wise to have snotsiekte confirmed (at least when the first animal dies).
In both the sheep and wildebeest types it was previously thought that avoiding close contact with cattle was sufficient to prevent transmission but now it is generally accepted that 1000m distance between them is needed; this is unfortunately not always practicable. Until 1993 the movement of wildebeest was restricted and regulated by the Directorate of Animal Health but these restrictions have now been lifted.
Attempts at making a vaccine have so far also failed. This makes the control of snotsiekte very difficult.