Zoonotic Infection Flashcards
Describe Rickettsia, Ehrlichia, and Coxiella
short, obligate intracellular, gram negative rods (note that they express LPS similar to gram negs, but don’t gram stain well)
Describe the pathogenesis of Rickettsia and related microbes
Virulence determinants?
Upon cutaneous infection, vasculitis is typically produced in the endothelial layer of the infected blood vessel wall and progresses to skin rash caused by hemorrhage and edema resulting from damage.
No exotoxins or cytolytic enzymes have been produced but its believed endotoxin production is a main player in fever and petechia characteristic of these infections
What causes Rocky Mountain Spotted Fever?
Rickettsia rickettsii
How is Rickettsia transmitted to humans?
ticks mostly via dogs
When do most cases of RMSF occu?
Pt. pop?
Areas commonly impacted?
Most cases are pediatric with transmission occuring primarily in the spring and summer months and VASTLY in GA, NC, and VA.
How does RMSF present? Mortality?
-acute onset of flu-like symptoms that include fever, myalgias (especially in the calves), HA, and prostration.
Rash then develops within 2-6 days of acute symptoms, starting at the ankles and wrists, and progressing to the trunk, palms, and soles.
delirium and coma can occur, as well as DIC and edema.
Fatal if untreated about 25% of time
How is RMSF diagnosed?
Pt. history of potential exposure and confirmed by serology using the Weil-Felix test or IFA (below)
How is a Weil-Helix test performed?
Slide metho
On a solid surface (glass slide, tile, card), a small amount (50–100 μL) of the patient’s serum is placed. A single drop of the desired antigen is added, and the resulting suspension is mixed and then rotated for one minute. Visible agglutination is indicative of a positive result, and corresponds roughly to a titer of 1:20. Positive results can be further titrated using the tube method, which is more labour-intensive.
Tube method
Using 0.25% phenol saline as a diluent, a series of tubes containing twofold dilutions of patient serum are made with a final volume of 1 mL. A drop of antigen suspension is added to each tube, and the mixture is incubated at 50–55 °C for 4–6 hours. A positive tube would show visible flocculation or granulation, which is accentuated when the tube is gently agitated. The titer corresponds to the most dilute tube in the series that still shows positivity. Generally, a titer of ≥1:320 is considered diagnostic.
How is RMSF treated?
Doxycycline
Describe the epidemiology of Epidemic typhus (Richettsia prowazekii).
transmited to humans via lice (but not actually believed to be zonootic but may be in flying squirrel) and from human to human after being shed from the lice in feces as they feed on the host
How does Epidemic typhus present?
high morbidity/mortality disease that begins with sudden onset of flu-like symptoms lasting for 1-3 weeks and then rash development 5-9 days after that.
Severe cases can have cardiac or CNS involvement and if left untreated, the death rate is from 10-60%
How is the rash of Epidemic typhus different from that of RMSF?
it spreads from the trunk to the extremities and is not observed on the palm or soles.
How does death typically occur in Epidemic typhus?
bacterial pneumonia or vascular collapse
How is Epidemic typhus diagnosed?
IFA and ELISA to visualize bus in infected tissue or to measure increase in anti-R proazekii Abs (4 fold increase)
Weil-Felix not used
How is Epidemic typhus treated?
doxycycline or tetracycline DOC with chloramphenicol being the next choice
What causes Endemic typhus?
Rickettsia typhi
How is rickettsia typhi trasmitted to humans?
rat fleas (small mammals are reservoirs (rats, opossums))
How does endemic typhus present?
Diagnosis?
Treatment?
Similar to epidemic typhus except that the symptoms are significantly less severe and mortality is rare even when untreated
Diagnosis: via serology
Treatment: Doxycycline
What are the bugs of the Ehrlichia species?
Ehrlichia chaffeensis and Anaplasma phagocytophilia (formerly known as Ehrlichia phagocytophilia)
these bugs cause southern tick-borne disease
What tick transmits anaplasmosis? Ehrlichosis?
Anaplasmosis- blacklegged rick or Ixodes ticks
Ehrlichiosis- Lone Star deer tick
What disease does Ehrlichia chaffeensis cause?
human monocytic ehrlichiosis
What happens once Ehrlichia chaffeensis enters the body?
Diagnosis?
The obligate intracellular pathogen infects and replicates within monocytes
Dx: blood smear showing MORULAE (below) in monocytes is diagnostic- which is then confirmed via serology. NOTE: the Weil-Helix test does not work for this organism
Where is Ehrlichiosis common?
How does Ehrlichiosis present?
flu-like symptoms (fever, chills, malaise, and muscle pains) with additional symptoms such as GI problems, cough, and conjuctival injection.
Around 60% of children develop a skin rash, while only abut 30% of adults do.
How is Ehrlichiosis treated?
Doxycycline
Describe anaplasmosis phagocytophilia.
What is it transmitted through?
Mortality rates? What are the main causes?
Disease caused by anaplasma phagocytophilia (aka rocky mountain spotless fever) trasmitted via Ixodes ticks that presents variably with symptoms ranging from fever and HA to muscle pains, cough, confusion, and malaise.
Although it is assoicated with high morbidity, it is very rarely fatal (due to hemorrhage, renal failure or neurological problems).
How is Anaplasmosis diagnosed? Tx?
Diagnosis depends on area of interest and morulae in NEUTROPHILS (below)
Tx- doxy
Describe coxiella burnetii. Main reservoirs?
How does transmission occur?
obligate intracellular gram neg rod (considered one of the rickettsial diseases) that primarily inhabits cattle, sheep, and goat.
Transmission occurs via ingestion or contact with contaminated milk or dairy products or animal viscera (aka during birthing) OR via ticks
Main states for lyme disease?
NY, NJ, Pennsylvania, and Connecticut are responsible for 80% of cases
How does Stage 1 Lyme disease present? Describe the rash
painless, non-pruritic rash (bull’s eye or erythema chronicum migrans) between 3-30 days after transmission that may be accompanied by fever, chills, or arthralgias.
Describe Stage 2 of Lyme disease. When does it start?
begins weeks to months later and is characterized by cardiac (myocarditis and various forms of heart block) and neurological symptoms such as Bell’s palsy (below). Bilateral facial nerve palsy is highly suggestive of Lyme disease.
How is relapsing fever diagnosed? Tx?
visualization of spirochetes on blood smear (serology is of little value)
Tx: tetracycline or doxycycline
What are leptospira and how can they be seen?
tightly-coiled spirochetes
do NOT stain well with dyes, but are sometimes visible via dark field mircoscopy
Describe Bartonella heneslae
- small gram neg rod
- pleomorphic under staining
- has polar flagellum
How does cat scratch fever present? Progression?
usually self-limiting infection primarily seen in children that begins with fever and tender, enlarged lymph nodes (below) near the bite. A papule may be observed prior to the development of nodes.
The disease typically has a long course but resolves without treatment in those who are immunocompetent.
How is SCF different in immunosuppressed patients?
bacillary angiomas can occur in the skin or visceral organs
What is the incubation period of anthrax?
How does anthrax present?
between 2-12 days and sometimes even faster.
At the infection site, a painless lesion develops that includes edema. Subsequently, the lesion becomes blistered and ultimately a painless necrotic center develops (called eschars).
Accompanying symptoms include dizziness, heart palpitations, lymphangitis, and sepsis without treatment
