Research Looks at Tick Diseases as Cause of Immune-Medicated Disorders
Tick populations are at an all-time high this year, experts say. Dogs are particularly susceptible to ticks — and thus tick-borne diseases — because they spend a lot of time outdoors and are low to the ground where ticks live. Since ticks do not usually transmit disease until 24 to 48 hours after attachment, owners can help prevent illness by promptly removing ticks.
A one-year study, funded by the AKC Canine Health Foundation, is investigating how undetected infections that are transmitted by tick and flea vectors may contribute to immune-mediated conditions, such as hemolytic anemia, thrombocytopenia (low blood platelets) and/or joint pain.
Lead investigator Linda Kidd, D.V.M., Ph.D., DACVIM, associate professor of small-animal internal medicine at Western University of Health Sciences College of Veterinary Medicine in Pomona, Calif., says, “I believe this study will contribute to other studies that help define the prevalence of tick-borne disease and help clinicians determine the best ways to test for underlying infections in dogs with signs that are similar to those signaling immune-mediated disease.”
Undiagnosed tick-borne infections in dogs with suspected immune-mediated disease may lead to treatment failure and the exacerbation of disease. In immune-mediated diseases, the immune system attacks the body inappropriately.
“It is thought that a trigger, such as an infection, drugs or cancer, may turn on immune responses that can be directed against self,” Kidd explains. “Genetic predispositions to immune-mediated disease also may contribute to disease development. Although a precipitating factor often is not found, these diseases can be managed better if you can find and treat the underlying causes. With tick-borne diseases that isn’t always easy.”
Kidd’s study will determine if comprehensive testing for tick-borne diseases using serology and polymerase chain reaction (PCR) screening, and testing more than one sample, makes it possible to detect infection in dogs that otherwise would be overlooked. Veterinary clinicians usually test one sample from a dog using serology or PCR, but not both tests. Serology detects the presence of antibody, which is one product of the body’s immune response against a pathogen, and PCR detects the nucleic acid, the DNA, of the organism itself.
“Although these tests are excellent, they can’t determine if infection is present or responsible for the clinical signs 100 percent of the time,” says Kidd. “For some diseases, the presence of antibody may mean the dog was exposed to an infectious agent but is not actively infected or the organism isn’t causing illness.”
For example, 50 percent or more of dogs living in Lyme disease endemic regions have positive titers when tested. Because exposure is common in healthy dogs, the test often is positive in these regions. Thus, it can be difficult to determine if clinical signs are due to Lyme or another disease.
A recently completed study at North Carolina State University College of Veterinary Medicine showed that using both serology and PCR together can help determine whether infection is present. Adam Birkenheuer, D.V.M., Ph.D., DACVIM, associate professor of internal medicine and director of the Vector Borne Disease Diagnostic Laboratory, says, “There is no perfect test for tick-borne diseases. A veterinarian should use a combination of historical information, physical examination findings, laboratory tests, and how well a dog responds to treatment to support or refute tick-borne infections.”
Diagnosis also can be tricky because the most common indicators of vector-borne disease in dogs are nonspecific, such as lethargy, decreased appetite and gastrointestinal signs. To further complicate matters, ticks often transmit multiple diseases simultaneously. Many infections are treatable but not with the same drugs. Dogs that are co-infected can become sicker longer, have more severe clinical signs and require a longer treatment regimen.
The bottom line is that diagnosing tick-borne disease is complicated. Dog owners should work closely with their veterinarians to determine which infections are most likely and which testing should be performed.
Owners also should be aware that dogs are sentinels for some vector-borne diseases in people, becoming sick before their human companions. People who feel ill should contact their doctor immediately. Preventing tick and flea infestations is extremely important for your health and that of your dogs.
Common Tick-Borne Diseases in Dogs
|Lyme Disease||Black-legged tick (deer tick)||Borrelia burgdorferi||Lameness, hot or swollen joints, fever, fatigue, and lack of appetite. Heart, neurological or kidney damage may occur.|
|Anaplasmosis||Black-legged tick (A. phagocytophilum). The vector for A. platys is not known but is thought to be tick transmitted.||Anaplasma phagocytophilum and Anaplasma platys||Low blood platelets and fever (A. platys and A. phagocytophilum). Anemia, lethargy, lack of appetite, enlarged lymph nodes, and stiff joints (A. phagocytophilum).|
|Ehrlichiosis||Brown dog tick||Ehrlichia canis||Anemia, low blood platelets, ocular and neurological signs, fever, swollen lymph nodes, runny eyes and nose, nosebleeds, lethargy, lack of appetite, and exercise intolerance.|
|Rocky Mountain Spotted Fever||American dog, lone star and wood ticks, and in some areas the brown dog tick||Rickettsia rickettsii||Fever, swollen lymph nodes and joints, vomiting, stiffness, skin lesions, vision problems, nosebleeds, anemia, and neurological signs (behavioral changes, head tremors, difficulty standing or walking).|
|Babesiosis||Brown dog tick (B. canis). B. gibsoni is thought to be transmitted when an infected dog bites an uninfected one.||Babesia canis and Babesia gibsoni||Anemia, pale gums, weakness, anorexia, vomiting, and low blood platelets.|
|Bartonellosis||Ticks and fleas may be vectors in dogs||Bartonella vinsonii, Bartonella henselae and other species||Intermittent fever and lameness. May cause anemia, heart or liver disease among other signs.|
|Hepatozoonosis||Brown dog and Gulf Coast ticks (transmitted when dogs eat infected ticks or animals)||Hepatozoon canis and Hepatozoon americanum||Back pain, fever, runny eyes and nose, bloody diarrhea, muscle pain, muscle wasting, and other signs may occur due to infection of spleen, bone marrow and muscles. Signs vary with species.|
* Note that the listing of signs is not comprehensive. Additional signs may occur with each disease.