A study conducted by the University of Wisconsin-Madison School of Veterinary Medicine Clinical Assistant Professor Erin Lashnits provides new information on how best to diagnose Bartonella infection in dogs, a common disease transmitted by fleas that is linked to heart infection, organ inflammation and other conditions.
The researchers assessed the clinical accuracy of six different diagnostic tests for Bartonella infection in dogs. They found that the most commonly used tests had very low sensitivity, which can lead to false negative results. At the same time, a less common test method was very accurate.
The results, published in June in the journal Pathogens, could help improve diagnostic techniques applicable to both companion animals and humans, since the definitive diagnosis Bartonella infection in veterinary and human patients remains difficult. Lashnits says the findings address “a big open question in veterinary medicine.”
There is currently no benchmark test for Bartonella in dogs, and there was also no precise estimate of the clinical sensitivity and specificity of many of these tests. These limitations have made it difficult for veterinary clinicians to critically interpret test results, for epidemiologists to draw appropriate conclusions about population-wide trends around. Bartonella infection in dogs, or for scientists to explain the modes and routes of transmission.
“A clear understanding of the accuracy of commonly used tests for Bartonella was a big gap in the diagnosis, ”says Lashnits, a board-certified veterinarian in internal medicine for small animals. “The lack of a benchmark test limits our ability in the veterinary field to accurately estimate the incidence or prevalence of Bartonella infection in dogs.
Bartonella bacteria are historically associated with cat scratch disease, although it is only one of many acute or chronic conditions caused by many species of Bartonella. Bacteria are found all over the world, both in humans and animals. Animals can be infected with Bartonella by exposure to fleas and potentially ticks, which are natural vectors of the bacteria, or by exposure to cats or wild animals in the wild and to the fleas these animals can carry.
For this retrospective study, the research team compared the results of Bartonella diagnostic tests on clinical samples banked from 90 dogs with naturally occurring hemangiosarcoma, a cancer of the blood vessels. They used two different methods to analyze the performance of different tests on two key parameters: sensitivity and specificity.
Sensitivity is the ability of a test to correctly identify patients with disease, so high sensitivity means there are few false negative results, and therefore fewer cases of disease are missed. Specificity is the ability of a test to correctly identify people who are free from the disease.
The findings could help improve diagnostic techniques applicable to both companion animals and humans, addressing “a big open question in veterinary medicine.”
Researchers have found that performing a quantitative polymerase chain reaction (qPCR) – a lab technique that detects specific DNA molecules, in this case Bartonella genes – on freshly frozen tissue biopsy samples, provided the highest diagnostic accuracy, with high sensitivity and specificity. This is an important finding, Lashnits notes, because it is not a type of sample that clinicians would otherwise submit routinely.
Conversely, blood qPCR and indirect fluorescent antibody (IFA) tests, which are commonly used by veterinarians to diagnose Bartonella infection, had extremely low sensitivity with moderate specificity. Low sensitivity means that the tests are more likely to give false negative results, even when dogs are actually infected.
“IFA and blood PCR are the two most common tests used to diagnose Bartonella in dogs, it is therefore important for clinicians to remember that negative results from these tests do not preclude Bartonella infection, ”says Lashnits. “In fact, in this study, all but two of the 56 dogs classified as infected with Bartonella had negative results on both IFA and blood PCR.
The team would like to conduct a similar analysis of the diagnostic accuracy of Bartonella tests used in human medicine. While some diagnostic tests are well studied in some manifestations of bartonellosis in humans, uncertainties remain about the accuracy of other tests, particularly in patients with chronic symptoms and atypical presentations of the disease.
Researchers hope the information from this most recent study will help vets diagnose Bartonella in patients and help veterinary epidemiology researchers to better characterize the frequency, pattern and causes or risk factors of Bartonella infection in dogs.
The clinical manifestations and sequelae of Bartonella infection in dogs are still under investigation. The first case of Bartonella infection in a dog was documented in the 1990s, “so there is still a lot of work to be done,” according to Lashnits.
The best described presentation in dogs is endocarditis, an infection of a heart valve. Bartonella is estimated to account for 15 to 30 percent of all cases of endocarditis in dogs. Bartonella Infection in dogs can also lead to inflammation of 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 hemangiosarcoma, the disease affecting dogs in the new study, which Lashnits is currently studying in collaboration with researchers at North Carolina State University.
“Ultimately, if we can use these diagnostic techniques to diagnose and treat Bartonella early infection, we may be able to prevent the poorly understood consequences of chronic infection in dogs and humans, ”says Lashnits.
Earlier this year, Lashnits also published research showing evidence of Bartonella infection in the blood of people with schizophrenia and schizoaffective disorders. The researchers plan to conduct a larger study to see if these preliminary results are confirmed.
This work was supported in part by the American Kennel Club Canine Health Foundation (CHF Grant No. 2550).