Diagnosis, treatment of tick-borne diseases - DVM
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Diagnosis, treatment of tick-borne diseases
Some cases difficult to detect or fail to respond to therapies



Bartonella vinsonii and B. henselae appear to be the primary causes of bartonellosis in dogs. The full spectrum of canine diseases caused by Bartonella species has yet to be elucidated. Bartonella species have been shown to be a cause of endocarditis and have been associated with granulomatous inflammation and hepatic disease in dogs.

Although polyarthritis has been confirmed only in a handful of cases of canine bartonellosis, lameness and stiffness are the most common presenting signs for dogs with confirmed Bartonella endocarditis, suggesting that it may be a more common finding.

Anemia and thrombocytopenia have been detected in nearly half of the dogs diagnosed with Bartonella vinsonii.

The pathogenicity of Bartonella infection in cats is unclear, and it has not consistently been found to have any specific or characteristic hematologic or biochemical effects. Some studies have detected an association between stomatitis and lymphadenopathy in cats co-infected with Bartonella and FIV, while other studies have not detected associations between Bartonella and clinical diseases in cats.

Serology is suggestive of exposure or infection. And positive PCR test results are indicative of current infection. PCR tests should help identify and differentiate which species of Bartonella are present. A combination of culture (BAPGM) and PCR appears to be an excellent method for the detection of Bartonella species. For unknown reasons, there are frequently discordant results between serological and molecular/bacteriologic assays, so a combination of these techniques is recommended.

The optimal treatment for bartonellosis is unknown. Currently animals are being treated with azithromycin (5-10 mg/kg PO Q24 for five days, then every other day for 45 days). Some cases have had additional clinical responses when rifampin was used in combination with the azithromycin.

Since the full spectrum of disease is unknown and a large percentage of normal animals can test positive for Bartonella, cautious interpretation of test results is warranted and consideration of alternative diagnoses when animal signs fail to resolve with treatment. Humans, especially immune-compromised people, have been infected with Bartonella.

Rocky Mountain Spotted Fever)

RMSF caused by Rickettsia rickettsii is an acute systemic disease of dogs and humans. It generally is seasonal (April to September) correlating with the tick Dermacentor species life cycle.

Thrombocytopenia is the most common hematologic abnormality (>85 percent). The degree of thrombocytopenia ranges from moderate (about 75,000 plt/ul) to severe (< 5,000 plt/ul).

The primary mechanism is consumption secondary to vasculitis, but there is some evidence for immune-mediated destruction. Leukocytosis is the second most common hematologic finding. The degree of leukocytosis can be severe (> 50,000 WBC/ul), and tends to increase along with the duration of the disease. RMSF commonly is not known to cause immune-mediated hemolytic anemia. The anemia associated with RMSF often is mild (PCV 25-30 percent). The hematologic effects rarely are seen without accompanying clinical signs, such as fever, lethargy, anorexia, pain, petechia, jaundice and neurologic signs. Common serum chemistry abnormalities identified in dogs with RMSF included hypoalbuminemia, hyponatremia and hyperbilirubinemia.

Serology helps in diagnosing RMSF. If signs are acute, then paired acute and convalescent (two to four weeks after the acute) titers should be submitted to the lab. A four-fold change is diagnostic for an active infection.

If the dog is sick > 10-14 days, then a single high titer (> 1:1024) is consistent with an active infection. Positive Immunofluorescence of skin biopsies or positive nested PCR results also indicate active infection. Response to therapy (doxycycline, tetracycline, enrofloxacin or chloramphenicol) is suggestive but not diagnostic.

Doxycycline (5 mg/kg BID or 10 mg/kg Q24), chloramphenicol (15-30 mg/kg TID), and enrofloxacin (5 mg/kg BID) for two weeks are effective treatments. Resistance has not been reported, so if signs persist after treatment an alternative diagnosis should be considered.

An accurate diagnosis is important, because the dog can serve as a sentinel for human infections. A convalescent titer is indicated even if the animal has responded to treatment. Resistant RMSF has not been reported. RMSF has not been reported in cats. Casual contact should not pose a major risk, but direct exposure is a potential. Also, common vector transmission is possible (sentinel).


Source: DVM360 MAGAZINE,
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