Ehrlichia canis is an intracellular gram-negative bacterial blood parasite transmitted by ticks. It belongs to the order Rickettsiales, which also includes Lyme's disease and Rocky Mountain Spotted Fever. It is a particularly difficult parasite to deal with because most dogs do not build immunity. They can get infected, be treated and cleared, and be reinfected shortly thereafter. Repeatedly. Many dogs do not even produce antibodies. The purpose of this article is to try to educate the dog owners so that they may better understand and recognize this disease and learn to deal with it. The area we live in is an endemic zone for canine ehrlichiosis; most all dogs are going to be exposed sooner or later.
A dog becomes infected with ehrlichia when bitten by an infected tick. Before talking about the transmission of this disease, it is important to understand the tick's life cycle. The brown dog tick is the most common carrier, although other species of ticks can also transmit it. Most ticks have a life cycle consisting of three life stages although some have only two.
A gravid female tick lays up to 10000 eggs, depending on the species. Within a few weeks, these eggs hatch and the larva are released (1st phase). These are very tiny, about the size of a pin head, and have six legs. They usually stay together in a clump, and then grab on to the first animal that walks by (you may find your dog covered with hundreds). The larva attach, fill up with blood and fall off. They then crawl to a dry place (or up a wall) and molt into the next phase (nymphs).
The nymphs (2nd phase) emerge flat, medium sized and have eight legs. These find a new host and fill up with blood again, then fall off and wait to change into the 3rd phase (adult). The adult emerges flat, bigger, and sexually mature. The adult female tick engorges with blood on her third host. She will be found with several male adult ticks stuck all around her, to fertilize her eggs. After she is full of blood, she drops off and crawls to a safe place. Within several weeks, she will lay her eggs and then shrivel up and die.
There are different species of ticks, but many times the ones you find on your dog may just be different stages of the same type of tick. They can live up to 500 days before finding a new host and feeding again during any stage of their life cycle. It is important to note, where there are ticks there are many tickborne diseases. It is not surprising for a given patient living in a tick area to be cross infected with multiple blood parasites.
The way dogs get infected with Ehrlichia is fairly simple. All current research indicates thus far that there is no transovarial transmission of the parasite (from mother to offspring).
Basically, newly emerged 1st phase ticks are “clean”. If they feed on an infected host (a dog infected with Ehrlichia), they become infected with the parasite. Later, in another stage, if these infected ticks bite a “clean” dog, this dog can be infected. Phase two and three ticks are the potentially dangerous ones. Therefore, the only way to prevent your dog from getting Ehrlichia is by preventing ticks, which needless to say is almost impossible.
Once infected, the dog enters into the acute phase of the illness. In the most common presentacion of the acute phase, the dog will manifest fever, anorexia, enlarged lymph nodes, lethargy, and glassy, runny, eyes. There may be hemorragic tendencies due to platelet destruction such as subcutaneous petechial bleeds, bleeding of the gums or nose, bleeding in the sclera (white part of the eye), blood in urine, feces or vomit, corneal edema (they look slightly blue), ataxia, and rarely paralysis. A few dogs will die in this phase without immediate medical attencion. Contrarily, a particularly stoic dog will simply appear to be “off”.
The most common laboratory findings at this time are a moderate to severe drop in the platelet count, mild to moderate anemia and a mild white count decrease. Many times an ELISA snap test (a quick test that detects antibodies) will be negative; either because it is a recent infection and the animal has not yet produced antibodies, or because the dog is not capable of producing antibodies.
When a dog is in the acute phase
and presenting fever, it is the BEST time to treat. During the acute phase the parasite is circulating in the blood stream and easier to kill. Most dogs clear the organism if they are treated in this stage but those that do not receive adequate treatment will go on to the next phase (subclinical). When not treated, the dog will generally appear to get better on his own within
2 to 4 weeks which can be very deceptive. Very
rarely a dog with a competent immune system can successfully eliminate the bacteria and therefore not enter into the subclinical stage.
A dog in the subclinical stage of ehrlichiosis will seem
to be recovered. Usually they are not 100%, but they
will start eating and be up and about again. In the days/months following a lot of little seemingly unrelated problems may occur. They may develop mange or skin infections. They usually become anemic. The blood parasite continues working at an unseen level and weakens the immune system. It hides in organs like the liver, spleen and bone marrow. Many dogs develop an enlarged spleen. Other dogs seem pretty much normal, especially to a dog owner that has never been through it before.
Unfortunately it is more difficult to treat at this time. Laboratory findings at this point may be a low to low-normal platelet count, mild to more severe anemia and a low white count. Dogs can pass several months to years in the subclinical phase before entering into the cronic stage of the disease. Symptoms include weight loss, bone marrow suppression, hemorraging, arthritis, kidney failure,
blindness (due to detached retina) and a high mortality rate.
There is treatment for ehrlichiosis, but it is most effective when treated in the acute phase. It consists of a long antibiotic cycle
with doxicycline, accompanied by imidiocarb, vitamins, and good nutrition to help regenerate blood. It is very important to complete the schedule as recommended or the treatment is NOT effective.
If you notice any of the above symptoms in your dog or that he just doesn't seem right, it is best to bring him in as soon as possible for a checkup and basic bloodwork. Most acute cases are curable. If not treated adequately at this time or simply not treated, it is can be very difficult to manage later on!
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