From a microbiological perspective, the ideal stealth organism would have very specialized growth requirements and a very long dividing time (slow bacterial replication), which would greatly contribute to a historical inability to isolate these bacteria in microbiology laboratories throughout the world, especially when using well-established and standardized diagnostic isolation techniques. Finally, these stealth bacteria would not induce a consistent or predictable pattern of illness in animals or human patients, thereby avoiding discovery because doctors would not appreciate a defined disease pattern indicative of infection with a specific disease-causing agent. By the very nature and derivation of the word, epidemics are generally recognized when a substantial number of individuals within a defined population develop a similar disease pattern.
In many instances, the onset of illness occurs within a relatively short period after acquiring the infectious agent (for example, influenza), thereby facilitating rapid recognition of a definable disease pattern. One way to miss an epidemic is to have the offending infectious agent induce variable disease symptomatology months to years after transmission, which would interfere with a clinician’s ability to use pattern recognition (as is typically done by infectious disease physicians and veterinarians) in an effort to correlate disease symptoms with a specific infectious agent.
Most pathogenic organisms (estimates include 60-75% of all known or emerging pathogens) are zoonotic, meaning the same organism can infect or induce disease in an animal and a human being. In some instances, the animal serves as a reservoir (a healthy animal that carries the organism in the blood, intestinal tract, skin, or urinary system, often for extended periods of time) for human infection, but, in many instances, the pathogen is opportunistic (i.e., takes advantage of low immune defenses) and induces disease of similar severity in animals and people. As a reservoir host for vector-borne organisms, animals maintain organisms primarily within the blood and the dermis (skin), and in most instances these organisms, which can be very prevalent in nature, do not induce disease in the animal reservoir host.
These same organisms (bacteria, protozoa, rickettsiae, viruses) can be mildly to highly pathogenic when introduced into a non-reservoir host.
Examples include children whose immune systems have not completely developed, the elderly who experience immune senescence (a natural progressive deterioration of immune function with advanced age), or other individuals within modern-day society who are immunocompromised due to HIV, alcoholism, or therapeutically to treat an immune-mediated disease (e.g., systemic lupus erythematosus, multiple sclerosis, rheumatoid arthritis). Thus, stealth organisms of low pathogenicity (low disease-causing potential) can induce chronic and insidious, or acute, serious and potentially fatal illnesses.
Because of improved science and diagnostic testing modalities, bartonellosis is now being documented in transplant recipients and in people and animals historically treated for autoimmune conditions with immunosuppressive drugs. Previously, these conditions were not accurately diagnosed as an infectious disease, as bacterial members of the genus Bartonella were not known to exist throughout North America and much of the world prior to the AIDS epidemic in 1990, another epidemic that was also not initially recognized or acknowledged as such. In conclusion, Bartonella species have evolved a stealth pathogen strategy over thousands of years, which may well have given rise to a hidden epidemic.
To learn more about Bartonella:
- Understanding Bartonella medical webinar
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- Bartonellosis, One Health Perspectives for an Emerging Infectious Disease
- Wolf, L.A., Cherry, N.A., Maggi, R.G., and Breitschwerdt, E.B., 2014. In pursuit of a stealth pathogen: Laboratory diagnosis of Bartonellosis. Clinical Microbiology Newsletter, 36(5), pp.33-39.
Dr. Breitschwerdt is an internist and professor of medicine and infectious diseases at North Carolina State University’s College of Veterinary Medicine. He is a co-director of the Vector Borne Disease Diagnostic Laboratory which has been testing animals for vector borne infections, including Bartonella since 1984 and Chief Scientific Officer at Galaxy Diagnostics.
Editor’s note: Any medical information included is based on a personal experience. For questions or concerns regarding health, please consult a doctor or medical professional.