Sweating sickness is a tick-borne, toxic condition that affects the skin and visible mucous membranes of cattle. The cause is a toxin attracted to skin, which is secreted by females of certain strains of the tick Hyalomma truncatum. Thus, it is not an infection. It is mainly a disease of young calves, although adults are also susceptible. It occurs in Eastern, Central and Southern Africa, and in Sri Lanka and India.
Mode of spread
The toxin develops in the tick, not in the calf. The potential to produce toxin is retained by ticks for up to 20 generations. The disease cannot be transmitted from an infected animal to a susceptible animal by contact or by inoculation of blood.
The severity of the disease depends on the length of time toxin-producing ticks spend on a susceptible animal. A very short period of time has no effect - the animal remains susceptible. A period just long enough to produce a reaction may confer immunity. But, if the exposure is longer than 5 days, severe clinical signs and death may result.
Recovery confers immunity which lasts for up to, and perhaps longer than 4 years.
Signs of Sweating Sickness
The severity of the disease ranges from the peracute (quick onset in the duration of a few hours only) to the inapparent, depending on how long the toxin-bearing tick has been attached. Clinical signs do not usually appear before ticks have been attached for about a week.
- Initial symptoms are fever, salivation, and reddening of the skin and visible mucous membranes.
- There is loss of appetite, watering of the eyes and nose, salivation, and tenderness of the skin.
- The skin feels hot and sometimes the eyelids stick together.
- A few days after the onset of fever a moist eczema appears. Sometimes this is generalised but more often it is localised to patches on the head, the neck, flank, axilla or groin.
- The hair is matted and sticks together with beads of watery fluid on the hair tips. Tufts of hair with skin attached can easily be pulled from these areas, exposing raw, red wounds.
- The skin is extremely sensitive and painful and has an unpleasant smell. The tips of the ears and the tail may slough.
- The coronets of the hooves sometimes become congested and very painful.
- The animal is distressed by bright sunlight and seeks shade. It resents being handled.
- It may have diarrhoea, nasal and oral erosions and a frothy nasal discharge. At this stage death may occur. If the animal does not die then the skin may become hard and cracked and predisposed to secondary infection or to fly maggot infestation.
Recovery is signalled by a resumption of appetite, but affected areas of skin remain thickened and corrugated. The hair is often shed from these areas- sometimes from the whole body- but regrows within 3-4 weeks.
Death in affected calves ranges from 30-70% and 100% of calves in areas where the disease is prevalent may be affected. This all depends on the numbers of ticks, the length of time they are on the host and the immune status of the herd.
In its usual form, Sweating Sickness disease is easily recognized. Very severe cases may on the surface be confused with other acute conditions such as Anthrax, Redwater, Heartwater, and mineral and plant poisoning. But an acute moist dermatitis in calves in conjunction with the presence of Hyalomma ticks should aid diagnosis. The disease is not widespread and is localised to areas where Hyalomma ticks are present. The finding of these ticks is crucial to diagnosis.
Prevention - Control - Treatment
Prevention and control
A tick infestation of at least 3 days produces immunity. Eradication of the tick is rarely possible due to the fact that the larvae and nymphs can feed on alternative hosts. Dipping or spraying are the means of control.
Using an acaricide with a 2-3 day residual action at 7 day intervals will allow the ticks to feed for about 4 days, and so produce a mild or inapparent reaction with subsequent immunity. If the ticks are attached for less than 3 days, no immunity is developed and, if attached for more than 5 days there is the possibility of severe reactions and heavy mortality.
There is no specific treatment, as this is not an infection.
The best course is to remove the ticks, treat symptoms by good nursing, provide appetising foods, and administer antibiotics and sulphonamides to suppress secondary infections of the skin, respiratory and alimentary tracts.