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Canine Trauma




Just What Are "Tick Titers," Anyway?
An Overview of Select Tick-Borne Diseases

by Celeste A. Clements, DVM, Diplomate ACVIM - VetCentric.com

With the advent of warm weather, our animal companions are at higher risk for exposure to ticks, arachnids that carry a wide array of diseases’some of which are serious. For that reason, you may hear your veterinarian throwing around the term "tick titers" quite a bit this season. He or she is referring to tests performed on your pet’s blood serum that measure their body’s production of antibodies against disease-causing organisms transmitted by the parasites.

These titers will help the veterinarian determine whether your pet has been exposed to a tick-borne disease’and if so, which one. This is important, as there are many different types of organisms that ticks carry.

Canine ehrlichiosis, Rocky Mountain spotted fever, and Lyme disease are commonly grouped as the "tick-borne diseases," but there are others. Canine babesiosis, canine hemobartonellosis, canine heptozoonosis, tularemia, and feline cytauxzoonosis are important diseases that may be caused by infections associated with tick bites, but they have a more limited impact on companion animals.

There is also the unique problem of tick paralysis: females of certain tick species produce a potent salivary neurotoxin that may cause your pet to become immobile.

Why are ticks so good at spreading bad diseases? The tick is well-suited to transmit infectious organisms from one host to another, because all of the parasite’s feeding stages subsist on blood. The hard ticks within the Ixodid family that spend three of four life phases’larva, nymph, and adult’on different wildlife and domestic animals are most efficient at spreading blood-borne infection. They attach to the host for days to months. During this time, the animal’s blood is re-circulated with the infected saliva of the tick, and this process maximizes the potential transmission of infectious particles.

When the titer tells you it’s canine ehrlichiosis

The term canine ehrlichiosis describes a group of related rickettsial diseases that infect dogs, producing inflammation within the blood vessels of different body systems. The parasite Ehrlichia canis is found worldwide, but exists in especially heavy populations in the Gulf Coast states and in the southwest, where Rhipicephalus sanguineus, the brown dog tick is concentrated.

There are three stages to canine ehrlichiosis: acute, subacute, and chronic. The acute phase of illness begins one to three weeks after infection, producing signs of fever, lymph node enlargement and pinpoint or paintbrush bruises on the skin and mucus membranes such as the gums. Lasting two to four weeks in most canine patients, this phase is the most easily recognized. Often, the immune system will be able to fight off infection during this stage.

However, if the immune system isn’t successful in its battle, the dog will enter the subacute phase’in which clinical signs will be less obvious, but not necessarily less harmful. Canine ehrlichiosis in this stage can produce important changes in the bone marrow and immune system of infected dogs. If not conquered by the immune system, the chronic phase of ehrlichiosis can progress to irreversibly damage the kidneys and bone marrow. Lameness, pale gums, and spontaneous hemorrhage may be most evident.

Fortunately, the prognosis for dog patients with ehrlichiosis is good if treatment is initiated during the acute or subacute phases. Doxycycline, a longer-acting tetracycline, is most frequently chosen to treat infected canine patients, and is administered for several weeks continuously. Supportive care may be indicated; blood transfusions and anti-inflammatory treatments may be necessary to stabilize some patients that are severely ill.

When the diagnosis is Rocky Mountain spotted fever

Affecting both dogs and people, Rocky Mountain spotted fever is caused by another rickettsial organism, Rickettsia rickettsii. The illness is seasonal, with occurrences through spring and early fall. The main tick vector species are Dermacentor andersoni and D. variabilis, also known as the Rocky Mountain wood tick and American dog tick, respectively, but other tick species may carry the organism. Human and canine disease is most prevalent in the central and southeastern United States.

The multiplication of the Rickettsia organisms in small vessels leads to profound inflammation, with leakage of tissue fluids, swelling, and severe organ damage. Small hemorrhages may appear as reddish-purple blotches under the skin.

If the disease is suspected, your veterinarian will act promptly to try to save your dog’s life; death is not uncommon. Usually, tetracyclines or fluoroquinolone antibiotics are used as treatment.

Eliminating Lyme disease

Tick titers are a good tool for diagnosing tick-borne diseases, but they certainly aren’t definitive when it comes to Lyme disease, which is caused by infection with Borrelia burgdorferi. Because of cross reactivity with other infectious organisms and elevated antibody titers in healthy dogs living in endemic areas, pinpointing Lyme disease is quite a challenge. Vaccination against the disease also may produce falsely positive results on screening tests.

A presumptive diagnosis of canine Lyme borreliosis may be based on combining positive antibody results with the presence of polyarthritis, exclusion of other causes of arthritis, and positive response to treatment. A Western blot immunoassay can discriminate between natural and vaccinal exposure. Improved criteria for diagnosis are being investigated, as are improved vaccines.

Lyme disease affects multiple mammalian species, including dogs, cats and horses, as well as human, but it may be more rare among pets than is commonly assumed. Ticks of the Ixodes genus residing along the Northeast coast, the upper Midwest and in northern California harbor the spirochete bacteria. Small mammals, lizards, and deer support the different life stages of the tick.

In documented cases of canine lyme borreliosis, mild fever, stiff gait and lameness from polyarthritis or joint inflammation are most common. The illness is likely to be self-limiting, but the organisms are rarely cleared from the body. Persistence of the bacteria can lead to chronic effects; rarely, chronic arthritis, cardiac and neurologic signs may mimic syndromes recognized in affected people.

With Labrador retrievers and golden retrievers, rapidly progressive kidney failure can occur as a result of Lyme disease. Doxycycline is considered the drug of choice for dog patients that require treatment for Lyme disease, but amoxicillin may be substituted for patients that fail to tolerate the drug or fail to respond to treatment.

Of the common tick-borne diseases only canine Lyme disease has a specific vaccine. Most experts advise that vaccination be reserved for dogs that reside or travel in endemic areas, and that emphasis be redirected toward tick prevention and control.

Protecting your pet against ticks

Successful transmission of some tick-borne pathogens requires sustained contact with infected ticks: Borrelia rarely produces important disease unless ticks are attached for one to two days, and Rocky Mountain spotted fever organisms are transmitted only after several hours of tick attachment.

To prevent ticks from doing their damage, pet owners should remove isolated ticks as soon as they observe them. Note that coming into contact with ticks can be risky for humans; bodily fluids from infected ticks may pose a health hazard. For safe tick removal, your best bet is to wear gloves. At a minimum, use a curved forceps or other tool to apply steady traction to the tick’s mouth parts. The engorged tick’s torso should be covered with a facial tissue to prevent contamination by the bodily fluids.

Burning the tick is to be discouraged: it may actually delay release, allowing more time for organism transmission to the pet. Veterinary professionals can assist with difficult situations or severe tick infestations, which may be best handled by dipping or shaving the pet.

The best way to avoid ticks altogether is to stay away from regions where they are prevalent. Of course, not everyone has the means to pick up and move to a tick-free state’so fitting your cat or dog with collar labeled for tick control may be your best bet. There also are topical products that protect against ticks.

Rarely, veterinarians may prescribe tetracycline antibiotics to be used prophylactically for prevention of infection when patients are exposed repeatedly to ticks. Unfortunately, the offending tick may never be seen, so exposure must always be considered a possibility.

For now, tick titers remain a useful screening tool for the veterinarian or to verify a clinical diagnosis.

Article republished here with permission from VetCentric.com
Copyright(c) 2000 by VetCentric.com

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