Unit 1: Gram Negative Bacteria
Bartonella henselae (Cat Scratch Fever)
Overview- Bartonella henselae is a gram-negative bacterium that causes cat scratch fever. There is no vaccine for this pathogen.
Transmission & Epidemiology- Transmission chain: a flea bites a cat, transferring the bacterium to the cat; the cat then scratches or bites a human, transferring the bacterium to the person.
Flea control in cats reduces risk; outdoor/feral cats are more likely to carry fleas than well-controlled indoor pets.
Human-to-human transmission is not the usual route for this pathogen.
Clinical Presentation- Primary signs at the site: redness of the skin around the scratch, possible pustules.
Systemic signs: low-grade fever is common; most cases are self-limiting and resolve without antibiotics.
Rare but serious complications can occur in extreme cases, especially in immunocompromised individuals (e.g., pericarditis, endocarditis).
Population & Risk Factors- Most commonly affects children.
Immunocompromised individuals can have a worse presentation.
There are not widely used population-level numeric surveillance figures for this pathogen.
Diagnosis & Management- Diagnosis is typically clinical (cat scratch fever) and based on history of cat exposure and lesion appearance.
Antibiotics are not routinely required; some clinicians may treat in selected cases, but the disease is usually self-limiting.
If antibiotics are used, they are reserved for complicated cases or immunocompromised patients.
Prevention & Public Health Implications- Prevention focuses on flea control and reducing flea exposure for cats; avoid rough play with animals that could lead to scratches.
No vaccine available; standard clinical education emphasizes recognizing exposure and symptom patterns.
Miscellaneous notes from the lecture- The instructor reinforces that exact spelling on exams is not strictly required as long as genus and species are identifiable.
The class aligns with nursing school emphasis: vaccines, transmission, and infection control are emphasized; exams heavily rely on content rather than slide memorization.
Some slide content shown by the instructor is not essential to memorize for exams.
Real-World Relevance- Recognizing cat scratch fever helps differentiate from other causes of skin lesions and fever after animal exposure.
Understanding transmission chains aids in advising patients on reducing risk (flea control, safe pet handling).
Bartonella quintana (Trench Fever)
Overview- Bartonella quintana is the agent implicated in trench fever; historically associated with warfare and poor living conditions; current relevance includes homeless populations.
Transmission & Epidemiology- Vector: body lice (Pediculus humanus corporis) transmit the bacterium between individuals.
Not transmitted human-to-human directly in the sense of respiratory or contact spread; instead, the vector (lice) facilitates transmission.
Associated with crowded, unsanitary conditions (historically in trenches; in modern times in homeless communities and shelters).
Clinical Presentation- Core symptoms: fever, headache, body aches, joint pains, and bone pain.
Duration of fever can vary; typical ranges discussed for exam purposes include:
> \text{1 month}
The disease is usually debilitating but not typically fatal; death can occur in rare cases or in immunocompromised individuals.
Endocarditis and splenomegaly are possible extreme manifestations.
Population & Risk Factors- High prevalence in homeless populations and settings where body lice infestation is common.
Exposed individuals (e.g., social workers or caregivers) can be at risk via contact with infested individuals or environments.
Diagnosis & Management- Serological testing can reveal antibodies indicating prior exposure; active infection can be more challenging to confirm clinically.
A few thousand diagnosed cases occur annually in the United States, with clustering in the South/Central regions and among homeless populations; numbers are often reported collectively with other rickettsial diseases.
Treatment, Vaccines & Prevention- No vaccine exists for Bartonella quintana.
Antibiotics can be used, particularly in more severe cases, but the disease is often managed supportively due to its typical self-limiting nature.
Prevention focuses on reducing body lice infestation: personal hygiene, access to laundry facilities, proper clothing, and lice control in the environment.
Because lice can spread among people in close contact, transmission risk extends to caregivers and social service workers.
Real-World Relevance- The discussion highlights the link between infectious disease and social determinants (homelessness, shelter conditions).
Emphasizes the importance of considering vector-borne transmission in differential diagnoses in appropriate epidemiologic contexts.
Rickettsia (Rickettsiae) — RMSF and Spotted Fever Group
Overview- Rickettsiae are vector-borne bacteria that include RMSF (Rickettsia rickettsii) and other spotted fever group pathogens.
No vaccines exist for these pathogens; doxycycline is a common and effective treatment when started early.
Pathophysiology- The bacteria primarily target endothelial cells of blood vessels, causing vasculitis and vascular occlusion.
Consequence: impaired blood flow leads to tissue hypoxia and necrosis in affected areas.
This mechanism underpins potential severe complications if treatment is delayed.
Clinical Presentation- Early symptoms are non-specific and can be easily mistaken for other febrile illnesses: fever, headache, fatigue.
Rash patterns are a key differentiator:
Early stage rash occurs in about 0.90 \text{ (90%)} of patients.
Of those with an early rash, about 0.50 \text{ (50%)} develop a late-stage rash, which presents as darker spots.
The appearance of a late-stage rash indicates more extensive physiological damage.
Transmission & Epidemiology- Transmission is via ticks; there is no human-to-human transmission for RMSF (vector involvement is required).
Geography and seasonality: most cases occur in the South and Central United States, especially in summer months due to outdoor exposure and higher tick activity.
Lyme disease, a different tick-borne illness caused by Borrelia burgdorferi, is more prevalent in the Northern United States; the epidemiology of tick-borne diseases varies by pathogen.
Population & Risk Factors- Older individuals are more likely to present with symptoms; exposure does not always produce symptoms, particularly in younger individuals with stronger immune systems.
Diagnosis & Management- Early symptoms are not highly specific; a high index of suspicion is needed when patients have outdoor exposure in endemic areas and present with fever and rash.
Patient assessment should include questions about outdoor activity, tick exposure, and recent travel or hiking, to differentiate tick-borne illness from other causes.
Case counts are difficult to pin down precisely because CDC groups all rickettsial diseases together for surveillance; estimates indicate a few thousand diagnosed cases per year in the United States. Rocky Mountain spotted fever serves as a reference point for discussing spotted fever group diseases and their clinical presentation.
Treatment, Vaccines & Prevention- Antibiotics, notably doxycycline, are effective, especially when started early.
Early treatment improves outcomes and reduces risk of severe vasculitis and complications.
No vaccine; prevention relies on avoiding tick bites and performing prompt tick checks after outdoor activity.
General tick avoidance strategies: wear long sleeves, long pants, hats, and perform thorough tick checks after outdoor activities (especially in summer months and southern regions).
Tick checks should be comprehensive (including hair and exposed skin), and clothing should be treated or changed after outdoor exposure.
Public health emphasis is on prevention, prompt recognition, and early antibiotic treatment.
Real-World Relevance- In clinical settings, particularly in urban or suburban areas in the South, clinicians should consider RMSF and other spotted fever group diseases in the differential diagnosis during summer.
The lecture points out the importance of recognizing non-specific early signs to prevent progression to severe disease.
Diagnostic, educational, and exam-oriented takeaways
Key concepts to remember- Transmission vectors:
Bartonella henselae: fleas for cats; cat scratches initiate human infection; no human-to-human spread.
Bartonella quintana: body lice as vector; no direct human-to-human transmission; associated with crowded living conditions.
Rickettsia (RMSF and spotted fever group): ticks as vectors; potential for severe vascular damage; no vaccine.
Common clinical patterns:
Cat scratch fever: local scratch site with redness; low-grade fever; usually self-limited.
Trench fever: fever with systemic symptoms; variable fever duration; potential endocarditis in rare cases.
RMSF/spotted fever: fever, headache, fatigue; early and late rash stages; rash progression indicates worsening vascular involvement.
Diagnostic approaches and prognosis:
Many of these diseases rely on clinical history and exposure patterns; serology can indicate past exposure (not always current infection).
Early antibiotic treatment improves outcomes in tick-borne diseases; no vaccines exist for these pathogens.
Public health and preventive strategies:
Flea control for cats, lice control for humans in overcrowded settings, and strict tick avoidance in endemic areas.
Study and exam strategy notes (lecture-specific guidance)
Exam culture and preparation- Exams emphasize content and clinical patterns over slide-by-slide details; expect synthesis from history, exposure, and symptom patterns.
Do not rely on old exam questions or Quizlet alone; expect new question banks each semester.
The instructor records lectures; if you miss class, you can request a recording to stay up to speed.
Practical clinical skills emphasized- Use patient assessment techniques (travel history, outdoor activity, exposure history) to differentiate between pathogens with similar presentations.
Understand the concept of transmission chains (vector-borne vs direct person-to-person) and how they influence prevention strategies.
Real-world relevance- The content connects clinical microbiology to nursing practice, including vaccine knowledge, symptom recognition, and public health implications.