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Tick Fever Babesia

Babesia is a blood parasite that infects and destroys red blood cells causing life-threatening anaemia. It is spread by ticks and is common in Hong Kong.

Currently Babesia canis and Babesia gibsoni are the only two species known to infect dogs.

Infection occurs when an infected tick bites a dog and releases the infection into the dog's bloodstream. New ticks pick up the infection by biting an infected dog.

Pregnant dogs can spread the infection to unborn pups.

The dog’s immune system recognizes the infected cells and destroys them leading to anaemia.

Severe inflammation may also develop in other body systems such as the liver, kidneys, eyes, brain and lungs.

Clinical Signs

The infection typically incubates for 2 to 3 weeks before clinical signs show and most dogs will clear the infection and never become ill, but may become carriers. When stressed at a later date they may come down with clinical illness.

Babesiosis can be classified as uncomplicated or complicated

-       In uncomplicated cases dogs are acutely ill with fever, depression, anorexia, pale gums and dark urine. Some dogs will become jaundiced with yellow gums and eyes, and some may collapse suddenly.

-       In complicated cases signs may include acute kidney failure, neurological disorders, swelling of the legs or breathing problems. Shock, vomiting and death may also occur.

Diagnostic Tests

Hong Kong laboratories currently offer PCR testing for Babesia, identifying the parasite DNA. A further test can also differentiate between Babesia canis and the more aggressive Babesia gibsoni.

The parasite may also be identified on a blood smear, but a large percentage of infected dogs may not display this, so a negative smear does not rule out infection.

Treatment

Treatments are aimed at clearing the infection and reversing the anaemia.

No known treatment clears all babesial infections.

Current treatment protocols include

-       Atovaquone and azithromycin combination for 2 weeks

-       Diminazene (“Berenil”) injection

-       Imidocarb (“Immizol”) injection

The current most recommended protocol is atovaquone/ azithromycin. Unfortunately some dogs may vomit these drugs and at Acorn we use a liquid variant of atovaquone which is far less likely to cause nausea.

It is highly important to understand that at present none of these drugs are currently licenced for the treatment of babesiosis in dogs in Hong Kong, but their use is well documented and dose rates well established.

Some dogs may require blood typing and blood transfusion if their anaemia becomes too severe during treatment. At Acorn we have blood typing kits and routinely keep blood available for transfusion.

Follow-up Care and Prognosis

Dogs that clear the initial infection but become carriers may have relapses when subjected to stress and females that test positive should not be used for breeding.

Prognosis is most favourable when the dog is caught before the anemia becomes too severe, and is also determined by the dogs response to drugs used.

Some animals may develop a secondary immune-mediated haemolytic anaemia after the original infection has cleared, where the body’s over-active immune response continues to attack red blood cells after the original cause has been removed.

Effective tick prevention is VITAL in any dog potentially exposed to ticks to reduce the risk of contracting this and other tick-borne diseases. We recommend monthly Frontline and an effective tick collar. Dogs with babesiosis may also have concurrent ehrlichiosis as ticks may carry both!