Ehrlichiosis is a serious parasitic infection of dogs, transmitted by ticks in warm or tropical regions and occasionally elsewhere. The most serious form of the disease has a long course of many months to years and usually proves fatal. Ehrlichiosis may be seen in dogs in non-tropical countries if the animals have travelled from areas where the parasite is common.
Ehrlichiosis is a serious disease of dogs most often caused by a microscopic parasite called Ehrlichia canis which is transmitted by ticks. The tiny parasites, belong to a group of organisms known as Rickettsiae. The disease is seen mainly in the Americas, Asia, Africa and southern Europe, i.e. warm temperate and tropical climates (but not Australia), and also Finland. Some other species of Ehrlichia can also cause related conditions, with reports of these diseases in northern Europe, including Sweden and Scotland.
The disease is known by a number of different names, e.g. canine rickettsiosis, canine haemorrhagic fever, Lahore canine fever and Nairobi bleeding disease. When the disease becomes chronic and severe it is called tropical canine pancytopenia (pancytopenia means abnormally low numbers of all blood cells).
The juvenile parasite is found in ticks. When a tick attaches to a dog to feed, the parasite can enter the dog in the tick’s saliva. Once in the body the parasites enter the blood cells where they can hide from attack by the immune system.
Often, dogs may be simultaneously infected with Ehrlichia and two other parasites: Babesia and Leishmania. Although closely related to a species of Ehrlichia which infects people, Ehrlichia canis is not considered a threat to human health itself.
Common signs are:
- Lack of energy
- High temperature
- Poor appetite
- Prolonged bleeding after injuries
- Tendency to develop infections
Other signs include vomiting, discharges from the nose and eyes, lameness, breathing problems and problems with coordination.
Dogs imported into areas where infection is common from parts of the world normally free of ehrlichiosis, are more likely to show signs than those born in areas where disease is common (although these may still be infected). German Shepherd dogs may be particularly prone to the disease.
After infection there is a period of 1-3 weeks when the dog appears normal. Signs of illness then develop. If untreated the signs of illness may last for several weeks after which the dog sometimes makes a complete recovery on its own. However, even after recovering from illness, a dog can be a carrier and may succumb to the condition again when stressed, e.g. by another disease or pregnancy.
Some animals develop a more chronic and serious form of the condition (tropical canine pancytopenia) which can eventually prove fatal after a variably long period (months to years).
In parts of the world where this disease is common, characteristic signs often lead to a suspicion of ehrlichiosis. If ticks have been found on the dog, then the suspicion is further increased.
Infection can be confirmed by examining the blood of the dog to look for the parasites inside blood cells. Often the number of blood cells is also reduced. Measurement of protein levels within the blood is helpful. Detection of antibodies to the parasite (made by the dog’s immune system) confirms that an infection has occurred.
The parasite can be killed by some antibiotics. Usually the drugs tetracycline or doxycycline are used. Treatment must be given for several weeks. Additionally, injection of a drug called imidocarb dipriopionate may be given to help prevent development of the severe chronic form of the disease.
Other treatments may be needed to support the affected animal, e.g. blood transfusions for severely anaemic dogs, vitamin supplementation etc. whilst they recover from the infection.
With proper treatment in the early stages, the outlook for the dog is good. If ehrlichiosis becomes chronic, however, the outlook is poor. The chronic form of the disease, tropical canine pancytopenia, cannot be cured.
Controlling ticks will prevent transmission of the disease. Various veterinary preparations are available to kill ticks or prevent their attachment to the dog. As the disease can be passed in infected blood, blood donors should be screened for ehrlichiosis before donating.
Dogs travelling in regions where ehrlichiosis is common need careful monitoring as they are very susceptible to contracting the disease.