The old adage that blood is sterile no longer applies.
Bartonella infections have been described as far back as the Inca Dynasty, and bacteria in red blood cells was first described by A. L. Barton in 1909. However, the significance of these bacteria in human and animal disease has only recently come to light.
There has been much research on bartonella in the last two decades. As of 2013, more than 20 species of bartonella have been described and the number of known bartonella species is expected increase.
Bartonella infection has been found in a variety of mammalian species, including cats, dogs, coyotes, ground squirrels, rats and people.
Among these newly discovered bartonella species is bartonella bovis, which infects cattle.
So why are these bartonella bacteria suddenly on our radar?
The bacterium is extremely difficult to culture using traditional laboratory methods because it lives only inside or on the surface of red blood cells and blood vessels. In fact, less than 10 percent of infections can be detected using these traditional techniques.
It wasn’t until advances in molecular testing came along that it could be accurately diagnosed. In this case, it was a matter of not being able to look for it rather than it being a new emerging disease.
Genetic analysis supports the theory that this bacterium has had a long-term co-evolution with cattle.
Because bartonella bovis has infected cattle for a long time, it is thought that the bacteria have evolved to cause minimal effects on its host, settling into a relatively peaceful co-existence.
This survival strategy is quite different from that of another bacteria, bacillus anthracis, which causes the rapidly fatal disease anthrax. Transmission of anthrax depends on the rapid death of the infected animal to release massive numbers of spores into the environment.
The vast majority of bartonella bovis infections cause no signs of disease in cattle. There are rare reports of bartonella bovis causing endocarditis, which is inflammation in the tissue that lines the heart, including the heart valves.
Cases of endocarditis in cattle are usually only diagnosed at slaughter or during autopsy examination.
The interaction between this bacterium and other pathogens such as BVD and bovine herpes virus remains to be investigated. It is plausible that infection with bartonella may have subclinical effects on reproduction and growth.
Blood-sucking insects, such as lice, biting flies and ticks, transmit this bacterium between cattle.
The percentage of infected cattle seems to vary between locations. For example, a 2008 study in North Carolina found that 82 percent of beef cattle were positive for B. bovis. Conversely, only seven percent of dairy cattle tested in a Polish study were infected. Prevalence of B. bovis in Canada is unknown.
Zoonotic potential of bartonella bovis is also unknown, but other bartonella species can cause infections in people. Veterinarians and other people with significant interactions with animals may be at an increased risk of exposure. The most notorious and well studied of these is bartonella henselae, which is carried by cats and causes cat scratch disease in people. Cats infect people through scratches and bites. Children are most often affected and the disease is usually self-limiting.
Humans have their own bartonella species, including one that causes trench fever. Homeless people are most commonly affected.
In immunocompromised people, such as those with HIV/AIDS, many bartonella species are associated with tumour-like growths in blood vessels.
The recent work on bartonella, including bartonella bovis, has made great progress in our understanding of these bacteria, but their impact on animal health remains to be investigated.