Just a case of ticks?” Have you heard about tick fever? Maybe you have ignored your pet dog for quite some time and then noticed that it had ‘bumps’ attached to its skin— some as big as raisins, while others look like ants.
What is ehrlichiosis in dogs? It’s a disease associated with infection by Ehrlichia canis and E. chaffeensis. These organisms infect almost all blood cell types and are seen with non-specific signs (fever, lethargy, and inappetence or lack of appetite).
While any given case of tick infestation may be viewed as a form of external parasite problem only, there exists a large body of clinical experience that indicates it goes beyond that. As a practitioner of small animal medicine, I have personally handled dogs with cases of canine ehrlichiosis that started as a harmless tick infestations with mild anemia as the only clinically perceptible consequence.
However, there were other dogs that I treated that had to be given transfusions as a result of intravascular hemolysis or the breakage of RBC (red blood cells) inside the blood vessel as a consequence of the consumption of RBC and therefore, anemia. Subsequent consultations reveal an increase in BUN (blood urea nitrogen) as well as elevated creatinine levels in the blood.
This dramatic change in blood chemistry should not be misconstrued as a radical or abrupt pathophysiology but rather, one of a slow, progressive, and an insidious consequence of chronic parasitism that was developing while the disease was undiagnosed. Since Ehrlichia destroys all forms of blood cells, RBC, and WBC (white blood cells) with platelets included, anemia becomes an obvious consequence.
However, how does one go about in explaining progressive kidney disease?
These parasites are very good in hiding in the WBC, therefore avoiding detection. This continual presence is greeted with hostility by the host (dog). The immune system is often prompted to manufacture antibodies as a response to the presence of the parasite as well as dead, dying cellular debris. WBC are infected by Ehrlichia and are then turned against RBC and platelets, causing the numbers of the latter two to decrease. The infection causes a widespread inflammation that further destroys other WBC; this process can be pictured as a house on fire doused with gasoline.
Meanwhile, the bloodstream is filled with dead, dying blood components as a result of the presence of Ehrlichia that the dog’s Immune system is desperately trying to eliminate. Since blood is ultimately filtered in the kidneys, all the debris find their way to the kidneys. The battle is swiftly followed by more inflammation.
This time, it’s not confined to just some obscure area in the body but is localized in the kidneys. The ensuing “fire” induces more inflammation that causes injury to surrounding kidney tissues.
All of the blood pumped by the heart reaches the kidneys. Since urine is simply a byproduct of blood filtration, it is not hard to imagine how the inflammation reaches the kidneys.
Picture a fire that is spread to neighboring buildings due to the use of accelerants. It won’t be hard to imagine the effect in the kidneys of a dog. Now, that is not all.
A hormone known as Erythropoietin, which is responsible for the production of RBC, is drastically reduced due to the damage inflicted on kidney cells. Anemia is worsened, and the potential for shock suddenly becomes imminent.
Thus, what started as a so-called “ordinary tick infestation” ends up as a life-threatening condition.
Moral of the story: Vigilance against tick infestation is key to an Ehrlichiafree dog. Prevention is better than cure. In instances such as these, always consult a veterinarian.
Source: Breitschwerdt EB: The rickettioses. In Ettinger St. Fleman EC (eds): Textbook of Veterinary Internal Medicine. Philadelphia, WB Saunders 2000, pp. 402-404.
This story appeared in Animal Scene’s July 2016 issue.
