Ticking off ticks
Dr. Deepa Katyal briefly reviews the pathogenesis, clinical signs, diagnostic approach, and treatment of two tick-transmitted diseases in dogs. Two of the most prevalent tick-transmitted diseases in dogs are Babesiosis and Ehrlichiosis, which are also a fairly common cause of morbidity and mortality in South Asia.
While Babesiosis is caused by either of the protozoal parasites Babesia gibsoni or Babesia canis, Ehrlichiosis is caused by infection with a rickettsial organism, Ehrlichia canis. Both diseases have a common vector, the brown dog tick Rhipicephalus sanguineus, which thrives in warm and humid environments. It is not uncommon for a dog to be infected with both organisms at the same time.
But the greatest challenge in battling tick-borne diseases lies in detecting and accurately assessing the signs. In most cases, the early signs are very subtle, and very often mimic those caused by other diseases.
It is an infectious blood disease, and progressive (haemolytic) anaemia, or destruction of the red blood cells, is the primary factor in the development of its symptoms. Also known as ‘Biliary fever’, this ailment in dogs has a lot in common with malaria in man. The process of transmission of parasites (Babesia canis) takes place 2-3 days after the tick attaches itself to the dog. The parasites migrate from the tick’s salivary glands into the host’s circulatory system, causing the tick bite fever. The parasite then enters and destroys red blood cells.
Clinical signs: Most dogs usually suffer from the acute or sub-acute forms of the fever, which can be recognised by the dog being listless or lethargic, losing his appetite, and running a temperature. However, when the fever reaches the per-acute (sudden and severe) form, it causes death within a few hours, since treatment at that stage is of little avail.
As the disease progresses, it may affect the spleen, liver, muscles, and circulatory, lymphatic, gastrointestinal, and respiratory systems. It also interferes with the replication of life sustaining cells in the bone marrow, as a result of which the immune system of the dog is severely reduced. Depending on which system has been most severely affected by the Babesia organism, infected dogs display a variety of symptoms such as?destruction of red blood cells, protein in urine, oxygen deficiency in the tissues, free haemoglobin in the urine, laboratory finding indicative of jaundice, reduction in the blood platelet count (which predisposes the dog to prolonged or spontaneous bleeding episodes), abnormalities in lymph system, kidney failure and liver disease.
Treatment and balanced diet?:?However, treatment should be given only after a positive diagnosis has been made by means of a blood test. Severely anaemic dogs should be given oxygen therapy and whole blood transfusions in addition to specific anti-babesial drug therapy. Imidocarb dipropionate at 5mg/kg of body weight by intramuscular injection is the drug that works in such cases. The treatment must be repeated after 14 days. Though the drug is generally tolerated well, sometimes there are side effects, which include transient vomiting, salivation, muscle tremors, and restlessness. If they occur, these signs can be controlled. However, the judicious use of glucocorticoids along with liver and vitamin supplements helps in speedy recovery. And while the treatment is on, it is important to avoid fatty foods, and the balanced diet should be imperatively supplemented with a tonic. A follow-up treatment may also be required if the dog does not appear to be responding to the initial treatment.
Canine Ehrlichiosis is also an infectious blood disease in dogs caused by a tiny rickettsial parasite (Ehrlichia Canis), which is injected into the dog’s bloodstream through tick bites. These parasites not only destroy red blood cells but also suppress the bone marrow functions. Additionally, the severe depression of the immune system caused by the disease, opens the door to secondary bacterial infections and other complications. Clinical signs?: In the acute phase of infection, Ehrlichiosis appears much like any other viral infection, with a reduction in cellular blood elements being its primary characteristic. Although the organism lives and reproduces in the white blood cells (leucocytes), it has a particularly devastating effect on the lymphatic system. And it ultimately affects the respiratory, circulatory, and central nervous systems, as well as the kidney, brain, liver and spleen. When affected, the dog often runs a temperature, may lose his appetite, and/or act depressed. Even the eyes may begin to have a glassy appearance.
Right diagnosis?:?However, the biggest failure has been to recognise and test for the disease. If the dog shows any of the above-mentioned symptoms, it is most advisable to take blood for a routine Complete Blood Count as well as Platelet Count. Blood smear testing will also give a clear picture in some cases. Serological tests such as the Indirect Fluorescent Antibody or IFA test, which looks for the presence of antibodies produced by the dog’s immune system, is also a good diagnostic aid.
Timely treatment?:?Even the vets should be cautioned against the use of steroids in a dog that may have Ehrlichiosis. Although some chronically infected dogs may need treatment with steroids, this should always be administered in conjunction with doxycycline and only as a last resort. In cases where the vet feels that the dog may have more than one disease, then Ehrlichiosis should be given first priority.
Most cases respond well to the treatment with the tetracycline family of antibiotics. Doxycycline is the preferred drug as it has less potential side effects. Inoculation as well as injectable antibiotics should not be administered to a dog suspected of having Ehrlichial infection, as there have been reports of reactions after this.
Another drug, Imizol, has also proved very effective in treating Ehrlichiosis. Due to the high dosage, it is advisable to administer vitamin B and K supplements since the dog’s ability to synthesise those vitamins in the large intestine is greatly reduced.
However, since there is no vaccine available against Ehrlichiosis, we should rely on reducing the dog’s tick population. This can only be done by regular use of approved tick control measures that may be recommended by your veterinarian.
(Dr. Deepa Katyal, MVSc (Mumbai), MVSt (Australia) is a vet from Chembur, Mumbai. She is the CEO of K-9 Klub for dog lovers. She can be contacted at 9819742557.)