What is Bartonella
Introduction
Bartonella, a genus of bacteria, has long intrigued scientists due to its zoonotic potential—its ability to transfer from animals to humans. This blog post delves into the world of Bartonella, particularly focusing on Bartonella henselae, a noteworthy species with global impact. With its primary vector being the cat flea, this bacteria is known for causing Cat Scratch Disease (CSD), a condition that poses unique challenges for diagnosis and prevention.
The Spread of Cat Scratch Disease
Bartonella henselae, the causative agent behind Cat Scratch Disease (CSD), maintains cats as its primary reservoir and the cat flea (Ctenocephalides felis) as its main vector. Notably, direct transmission between infected and uninfected cats is rare, underscoring the significance of an arthropod vector in the transmission cycle. In humans, scratches and bites from bacteremic cats can lead to infection. The highest incidence of CSD in the United States occurs in the southern states, and is more common among children aged 5-9, peaking from July to January.
Ticks and the Bartonella henselae Debate
The potential involvement of ticks in Bartonella henselae transmission has stirred controversy. While ticks have been established as vectors for various zoonotic pathogens, including Borrelia burgdorferi, the causative agent of Lyme disease, their role in transmitting Bartonella henselae has been a subject of ongoing research. Although studies have been conducted both in and outside the United States, questions remain about the true extent of tick-borne Bartonella transmission. Limitations such as small sample sizes in these experiments, lack of distinction between Bartonella species, and potential false positives raise doubts about the statistical relevance of these findings.
Tick Transmission
Is it possible?
Efforts to demonstrate tick transmission of Bartonella henselae have yielded mixed results. A study conducted in western Europe in 2009, demonstrated that under ideal conditions ticks can acquire Bartonella bacteria through a blood meal and the bacterium can survive in the ticks body. Ixodes ricinus ticks were allowed to feed on an artificial membrane filled with sheep blood that had been heavily spiked with Bartonella henselae. Salivary glands from the potentially infected ticks were incubated on sheep's blood agar, and Bartonella bacteria grew from them. In addition to this, salivary glands were injected into 2 healthy cats, which both became bacteremic after several days. What this study does not reproduce is natural tick encounters with real hosts, the bacterial load at which naturally infected ticks carry, and whether this bacterium can be transmitted during actual tick feeding as opposed to an artificial membrane.
How are these ticks being tested?
While several articles claim to have positive Bartonella spp. results from tick samples, it has recently come to the attention of the scientific community that the primers and probes that have long been used for Bartonella PCR testing may not be specific enough to just Bartonella species. Three nitrogen-fixing bacteria found in soil and leaf litter, Phyllobacterium spp., Ensifer spp. and Mesorhizobium, may be responsible for false positive Bartonella results. It is also known that Mesorhizobium may be in commercially bought molecular grade water, which is used during the DNA extractions in most laboratories. Realizing this problem, Tokarz (2019) targeted a region of the 16s rRNA gene, mitigating any non-specific amplification from the common soil bacteria. Further research is essential to confirm that positive Bartonella results are in fact Bartonella spp. and not just bacterial contamination.
Implications and Future Directions
While progress has been made, there's much left to explore regarding Bartonella henselae transmission. MedZu's extensive tick testing in the USA and adjacent countries offers insight into the prevalence of this bacterium in ticks. However, much of the research that has already been done focuses on Ixodes ricinus ticks, which are the main human biting tick in western Europe. The scarcity of European tick samples submitted to MedZu warrants additional investigation into potential European vectors.
For the general public, responsible cat ownership and hygiene practices are key to reducing the spread of Cat Scratch Disease. Regular hand washing after handling cats and maintaining feline flea and tick preventatives are effective strategies. Additionally, medical professionals should consider CSD in cases of prolonged fever of unknown origin, ensuring timely diagnosis and treatment.
Conclusion
Bartonella henselae, the bacterium behind Cat Scratch Disease, continues to pose intriguing questions about its transmission dynamics. While the debate about tick vectors persists, ongoing research and comprehensive studies are imperative to unravel the mysteries of Bartonella transmission and its implications for human health. As we strive for a deeper understanding, responsible pet care and vigilant medical consideration remain vital tools in preventing the spread of Cat Scratch Disease.