Also known as
Sweating sickness is an acute tick-borne toxicosis (condition caused by poisoning) characterized mainly by fever and a profuse, moist eczema (itchy rash) and hyperemia--excess blood supply to the skin and mucous membranes. This is primarily a disease of young calves, although adult cattle are also susceptible.
Sweating sickness is widespread in eastern, central and southern Africa, Sri Lanka and Southern India, and most common during spring and rainy seasons when ticks are abundant. It often affects very young calves that become sick after being bitten by ticks.
After an incubation period of 4–11 days, signs appear suddenly and include fever, loss of appetite, listlessness, watering of eyes and nose, redness of mucous membranes (gums, eyes, vulva), excess salivation, sloughing of membranes lining the mouth, and extreme sensitivity to touch. Later, the eyelids stick together. Affected calves look scruffy, depressed and weak.
Their skin feels hot, and a moist dermatitis develops, starting from the base of the ears, armpits, groin, and perineum (area between the anus and vulva or scrotum) and soon extends over the entire body. Hair becomes matted, and beads of moisture may appear on the hair.
Often the most noticeable sign in a sick calf is head-to-toe wetness, as if water has been poured over the animal. If you pull a strand of hair off the animal’s body, it pulls easily, exposing a red, raw wound, which leaves the skin open for infections.
Skin becomes extremely sensitive and has a sour odor. Later, the hair and outer layers of skin can be readily pulled off, leaving raw areas. Tips of ears and the tail may slough off. Eventually, the skin becomes hard and cracked and at risk for secondary infection or screwworm infestation. Affected animals show pain when moving, and seek shade.
Often, the disease course is rapid, and death may occur within a few days. In less acute cases, the course is more prolonged and the animal may recover. Mortality in affected calves is 30% to 70% under natural conditions. Morbidity (number of animals in the herd affected) in endemic areas is about 10%.
Severity of infection is influenced by number of ticks on the host animal as well as the length of time they remain on the host. The animal may become emaciated and dehydrated.
Although this disease does not kill calves in high numbers, the disease course is often rapid--and death may occur after a few days. If left untreated, about 30 to 40% of affected calves would die after 2 to 7 days of illness.
- Head-to-toe wetness
- Loss of appetite
- Watering of eyes and nose
- Redness of visible mucous membranes
- Excess salivation
- Sloughing away of tissues inside the mouth
- Weight loss
- Increased sensitivity to touch
The cause of sweating sickness is an epitheliotropic toxin (a toxin that affects epithelial tissues such as skin and mucous membranes) produced by females of certain strains of a specific tick, Hyalomma truncatum. The toxin develops in the tick, not in the host animal.
This tick’s saliva produces a toxin that some animals react to when bitten—somewhat similar to a person who is sensitive to bee stings. That’s why only a few calves get sick, even though the rest of the herd might have been bitten by the same kind of ticks. This disease is not an infection; it is a reaction to the toxin in the tick saliva.
Four tick salivary gland proteins are thought to be associated with sweating sickness. The potential to produce toxin is retained by the ticks for as long as 20 generations, and possibly longer. Attempted experimental transmissions between affected and healthy animals by contact or inoculations of blood have been unsuccessful. A tick bite seems to be the only route of transmission.
Different lengths of time of tick infestation of a susceptible host by “infected” ticks have different effects on the host. A very short period has no effect, and the animal remains susceptible to future tick bites. A period just long enough to produce a reaction may confer immunity, but if the exposure is more than 5 days, severe clinical signs and death may result. Recovered animals have an immunity, which may last about 4 years.
Other closely related forms of H. truncatum toxicoses have been reported. For diagnosis, it is essential to determine the presence of the tick vector.
Prevention of sweating sickness is based on elimination of these ticks. The only effective way to destroy them is regular, systematic dipping or spraying with a product to kill ticks.
It won’t help to separate a sick animal from the rest of the group in an effort to prevent further cases. For an animal to develop sweating sickness, there must be a tick bite. The only way this sickness can be controlled is by controlling the ticks.
Adult ticks often attach in the tail switch. Removal of these ticks, symptomatic treatment to try to alleviate pain, and good nursing care are important. Use of antibiotics that are nontoxic to the kidneys, and anti-inflammatory preparations are useful for treating any secondary infection.
Immune serum can be an effective specific treatment, although these serums are often associated with problems of donor availability, possible serum contamination, and the necessity for IV administration of a relatively large volume.
For treatment, broad-spectrum antibiotics, especially tetracyclines, can help control secondary bacterial infections so the animal can recover faster. Anti-inflammatory medications can reduce fever and discomfort. Some veterinarians also recommend mineral and vitamin injections to boost the immune system.
It also helps to keep affected animals away from sunlight, since sunburn can cause sloughing of the wet hair. Medications to soothe the skin and prevent sloughing of hair may also be beneficial.
Supportive care is crucial for young calves; milk should not be withhold from a calf suffering from this disease. It may be necessary to force-feed a calf by tube if it won’t nurse or drink milk.