A study by University of Wisconsin-Madison College of Veterinary Medicine, Clinical Associate Professor Irene Lachnites, provides new insights into how best to diagnose Bartonella infection in dogs, a common flea-borne disease associated with heart infection, organ inflammation, and other diseases. .
The researchers evaluated the clinical accuracy of six different diagnostic tests for Bartonella infection in dogs. They found that the most commonly used tests have very low sensitivity, which can lead to false negatives. At the same time, the less common test method was very accurate.
The results were published in June in the journal Pathogens, could help improve diagnostic techniques applicable to both companion animals and people, as definitive diagnosis of Bartonella infection in veterinary and human patients remains a challenge. Lachnitz says the findings touch on a “big open question in veterinary medicine.”
There is currently no gold standard test for Bartonella in dogs, and there has not previously been an accurate estimation of the clinical sensitivity and specificity of many of these tests. These limitations have made it difficult for veterinarians to critically interpret test results, for epidemiologists to draw appropriate conclusions about population-level trends about Bartonella infection in dogs, or for scientists to explain the routes and modes of transmission.
“The clear understanding of the accuracy of the commonly used tests for Bartonella was such a huge diagnostic gap,” says Lachnits, who is a board-certified veterinarian in small animal internal medicine. “The lack of a gold standard test limits our ability in the veterinary field to accurately estimate the incidence or prevalence of Bartonella infection in dogs.”
Bartonella bacteria is historically associated with cat scratch disease, although this is only one of many acute or chronic conditions caused by many types of Bartonella. Bacteria are found worldwide in both humans and animals. Animals can become infected with Bartonella through exposure to possible fleas and ticks, which are natural carriers of the bacteria, or through exposure to cats or wildlife and the fleas that those animals may carry.
In this retrospective study, the research team compared the results of diagnostic tests for Bartonella in stored clinical samples from 90 dogs with a naturally occurring vascular cancer, a blood vessel cancer. They used two different methods to analyze how different tests performed on two main scales: sensitivity and specificity.
Sensitivity is the ability of a test to correctly identify patients with a disease, so a higher sensitivity means there are fewer false negatives, and therefore fewer cases of the disease are missed. Specificity is the ability of the test to correctly identify people who do not have the disease.
The researchers found that performing quantitative polymerase chain reaction (qPCR) — a laboratory technique that detects specific DNA molecules, in this case the Bartonella genes — on freshly frozen tissue biopsy samples provides the highest diagnostic accuracy, with high sensitivity and specificity. This is an important finding, Laschnits points out, because this is not the type of sample doctors would routinely send out otherwise.
Conversely, serum qPCR and indirect fluorescent antibody (IFA) tests, which are commonly used by veterinarians to diagnose Bartonella infection, had very low sensitivity with only moderate specificity. Low sensitivity means that the tests are more likely to give false negative results, even when dogs are already infected.
“IFA and PCR blood are the two most commonly used tests to diagnose Bartonella in dogs, so it’s important for clinicians to remember that negative results in these tests do not rule out Bartonella infection,” Laschnits explains. “In fact, in this study, all but two of the 56 dogs classified as having Bartonella had negative results on both IFA and serum PCR.”
The team would like to perform a similar analysis of the diagnostic accuracy of the Bartonella tests used in human medicine. While some diagnostic tests have been well studied in some manifestations of Bartonella disease in people, there remains uncertainty about the accuracy of other tests, particularly in patients with chronic symptoms and atypical disease presentations.
The researchers hope that the information from this latest study will help veterinarians diagnose Bartonella infection in patients and help veterinary epidemiologists determine the frequency, pattern, causes or risk factors for Bartonella infection in dogs.
The clinical manifestations and subsequent effects of Bartonella infection in dogs are still under investigation. The first case of Bartonella virus infection was documented in a dog in the 1990s, “so there is still a lot of work to be done,” according to Lachnitz.
The most commonly described symptom in dogs is endocarditis, an infection of the heart valve. It is estimated that Bartonella is responsible for 15 to 30 percent of all cases of endocarditis in dogs. Bartonella infection in dogs can also lead to inflammation in various organs, especially the liver and lymph nodes, and more rare diseases of the blood vessels. There is also some evidence that the infection is linked to angiosarcoma, the disease that affects dogs in the new study, which Lachnets is currently investigating in collaboration with North Carolina State University researchers.
“Ultimately, if we can use these diagnostic methods to diagnose and treat Bartonella infection early, we may be able to prevent the poorly understood consequences of chronic infection in both dogs and humans,” says Lachnitz.
Earlier this year, Lachnets also published research showing evidence of Bartonella infection in the blood of people with schizophrenia and schizoaffective disorder. The researchers plan to move forward with a larger study to see if these preliminary results are substantiated.
A pilot study finds evidence of Bartonella infection in patients with schizophrenia
Irene Lachnitz et al, Comparison of serological and molecular assays for Bartonella species in dogs with hematosarcoma, Pathogens (2021). DOI: 10.3390 / Pathogens 10070794
Erin Lashnits et al, Schizophrenia and Bartonella spp. Infection: a case-control pilot study. Vector-borne and zoonotic diseases (2021). DOI: 10.1089/vbz.2020.2729
Provided by University of Wisconsin-Madison
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