Exotic and Biohazard Pneumonias II Flashcards
Descirbe Francisella tularensis
a gram-negative rod that has a pleomorphic appearance upon staining. It is also an intracellular pathogen that is well adapted for survival within macrophages
What are the biotypes of Francisella?
A- more severe and found mostly in the US
B- less severe in Europe
Virulence factors of Fancisella?
Ft produces an LPS that cannot be recognized by TLR-4 and may produce a capsule
How is Ft transmitted?
Ft can be transmitted via mites, lice, and ticks, with ticks being the most common
vector. These vectors acquire the bacterium from infected animals in the wild, and it should be noted that Ft is endemic in animals and has been isolated from >100 different animal species.
Acquired via contact of contaminated blood or water with skin abrasions.
Ingestion of contaminated food or water.
Inhalation of aerosolized Ft (results in the most severe form of disease)
What is the reservoir of Ft?
The actual reservoir of Ft has not been determined. It can survive in animals, in insects, in water, and in amoebas (maybe how it survives in water).
Where are most Ft cases clustered in the U.S.?
Arkansas and Missouri and Martha’s vineyard, MA
How are the majority of infections in the Midsouth transmitted?
Of the ulceroglandular type
and are typically contracted through contact with blood from infected animals via skin abrasions (e.g. hunters)
What is the LD50 of Ft?
less than 10 when inhaled (extremely pathogenic)
What is the most common form of Ft?
The ulceroglandular form (75%) that occurs when the infection is acquired through a skin lesion.
This form of disease is characterized by the presence of a skin lesion or ulcer at the infection site that is accompanied by pronounced bubo-like LAD of local nodes. This form of disease carries a 1-3% mortality rate BUT can disseminate to the lungs resulting in a much more serious disease.
Other forms of Ft?
- GI (via food)
- Oculoglandular
- Pneumonic
- Typhoidal
How does Ft present?
rapid-onset flu-like symptoms.
Many patients also present with prolonged low-grade fever and LAD. Most cases (75%) are of the ulceroglandular type and include a lesion at the inoculation site as well as bubo-like swollen regional
lymph nodes.
T or F. Patients are typically left with lifelong immunity to Ft if they survive the initial tularemic disease.
T.
How is diagnosis of Ft made?
agglutination testing that involves both acute-phase (if a sample was collected) and convalescent phase serum.
Fluorescent antibody staining of infected tissue can also be
performed.
Culture of Ft from patients is very rare due to both the lack of available media that will support growth of the bacterium and the inherent dangers to medical personnel.
Vaccine for Ft
An unlicensed vaccine, known as the live vaccine strain (an attenuated type B strain of Ft), is available to military personnel (but not to the general public) and an individual that has received the vaccine would test positive in agglutination testing, even in the absence of Ft infection. Luckily, only military personnel
and a select few other people have received this vaccine.
How is FT treated?
Streptomycin. No significant
development of antibiotic resistance has been noted for Ft
Hantavirus belongs to what family?
Bunyaviridae
Describe the structure of Hantavirus
enveloped, trisegmented, single stranded, negative sense RNA virus found mostly in the Middle East and Asia
How is hantavirus transmitted? Treatment?
aerosolized rodent excreta
Treatment: Ribavirin
What type of Hantavirus causes Hantavirus pulmonary syndrome?
Sin Nombre virus
How does HPS present?
mostly in healthy young adults and shows prodrome of ever and muscle aches, rapidly progressing to pulmonary edema and respiratory failure. Death usually occurs within 2-5 days
What is the primary carrier of Sin Nombre?
deer mouse (and some white-footed mice, cotton rats, and rice rats)
Note that guinea pigs, hamsters, and gerbils are not known to carry it
What is the incubation period of HPS before symptoms?
14-17 days
Initial signs of HPS?
fatigue, fever, myalgia of the large muscle groups (thighs, hips, back, shoulders), and headache lasting 3
to 5 days.
Later signs of HPS?
- coughing and SOB
- pulmonary edema and hypotension
How is HPS treated?
Requires early and aggressive
intensive care, focusing on electrolyte balance, oxygenation of the blood, and maintaining blood pressure.
Describe Yersinia pestis (plague)
gram-negative encapsulated rod that is well-adapted for survival and growth in
macrophages, and is classified as an intracellular bacterial pathogen.
What is the LD50 of Yp?
between 1 and 10 CFU when it enters via the respiratory route.
How does Yp look upon staining?
Bipolar staining pattern that makes it resemble a safety pin with a clear area in the center.
What is the main reservoir for Yp?
rats (In the U.S., prairie dogs). Almost all cases occur in Southeast Asia.
How is Yp transmitted from rats to humans?
via fleas. However, person-to-person transmission is possible via inhalation of aerosolized droplets containing Yp.
Aerosol transmission results in the most serious and always fatal (without early
antibiotic treatment) pneumonic form of plague.
What happens when Yp is introduced by fleas?
it spreads to the regional lymph nodes. Soon after this dissemination occurs, the lymph node becomes painful and very swollen.
What is the name of the initial affected nodes?
Buboes, and their appearance lead to the designation for the most common form of plague, the bubonic plague.
The infection typically becomes bacteremic, reaching high conc. in the bloodstream and
then disseminating to many organs.
Virulence determinants of Yp?
1) The polysaccharide-protein capsule protects against phagocytosis, allowing for dissemination via the bloodstream.
2) The LPS is an endotoxin that interferes with normal cytokine production by the various immune cell types that respond to the infection. This prevents the immune system from responding in an efficient manner to the infection.
3) Two proteins (the V and W antigens) that allow intra-macrophage survival and growth
4) A series of Yersinia outer proteins (Yops), that are injected by a type III secretion system into host cells, that inhibit phagocytosis and host cytokine production by phagocytes.
5) exotoxin
What are the forms of plague?
1) bubonic plague that typically results from vector-transmitted infection. This
forms begins with bubo formation.
2) The pneumonic plague, and always results when the bacterium is transmitted via the aerosol route, and it can sometimes result from dissemination of Yp to the lungs during bubonic plague.
The bubonic form of disease is 50% fatal, while the pneumonic form of disease is
essentially 100% fatal without early antibiotic intervention.
How does Yp present?
high fever, myalgias, and collapse due to extreme fatigue (prostration). Septic shock can occur and along with pneumonic disease is the primary life-threatening consequence of plague.
What are the symptoms of pneumonic plague?
- fever, headache
- cough, hemoptysis, dyspnea, chest pain
- muscle weakness
How is Yp diagnosed?
Geimsa or Wayson stains can reveal the typical “safety-pin” appearance of Yp, and both are superior to gram staining for this purpose.
Fluorescent antibody staining, using antibodies specific for Yp determinants can be performed using tissues collected from the patient.
Treatment of plague
ideally involves both streptomycin and tetracycline, but streptomycin can be used alone if necessary.
Because plague progresses very quickly, suspected cases should be treated ASAP instead of waiting for the results of staining and antibody titering.
Vaccine for Yp
A partially effective vaccine that consists of a formalin-killed whole Yp formulation.
Which forms of Yp is the vaccine effective against?
Bubonic but not pneumonic plague.
