Tick Borne Infections Flashcards
Describe Ricketssial pathogens
Small, pleomorphic gram negative coccobacilli that are obligate intracellular bacteria. Arthropod intermediate host. No flagellar motility but have actin-based motility
What are the ricketssial pathogens and what diseases do they cause?
Ricketssia spp.: spotted fevers and typhus
Orientia tsutsugamushi: scrub typhus
Scrub (bush typhus) is a ricketssial diease. What is the causal organism and its vector and reservoir?
Caused by orientia tsutsugamushi. Vector: mites (chiggers). Reservoir: rodents
What are the distinguishing features of scrub typhus?
Morbilliform rash, hemorrhaging and intravascular coagulation, vasculitis
There are 2 types of typhus. What are they and what are the 4 ways in which they differ?
Epidemic and endemic typhus. They differ by: causal pathogen, transmission mode, vector and reservoir
What cause epidemic typhus? How is it transmitted? What is its vector and reservoir?
Ricketssia prowazekii, it is transmitted form person to person
Its vector is lice and its reservoir is humans
What causes endemic typhus? How is it transmitted? What is its vector and reservoir?
Endemic typhus is caused by Ricketssia typhi and felis.
There is no person to person transmission and is transmitted from a rat flea bite or feces only. Its vector is a rate flea and its reservoir is rodents.
What distinguishes epidemic typhus from endemic typhus? How are they similar
Epidemic typhus is much more severe disease: prolonged fever, severe headache and myalgias, morbilliform rash.
Endemic typhus is similar clinically but milder than epidemic typhus.
Both are ricketssial diseases that cause vasculitis throughout the body
How is the rash progression of spotted fevers different from typhus?
Spotted fever rashes have a centripetal progression: they start at the extremities and spread to the trunk
Typhus rashes have centrifugal progression: they start at the trunk and spread to the extremities
How is Ricketssia spread to humans?
Humans are an accidental host of Ricketssia. Ricketssia is spread to humans through ticks during a blood meal
How are ticks infected with Ricketssia?
Ricketssia-free ticks must feed on bacteremic hosts such as mice, rats, rabbits, squirrels
How does Ricketssia cause vasculitis?
After transmission of Ricketssia from a tick to a human during a blood meal, the bacteria infects the endothelial cells of small blood vessels. They multiply intracellularly and spread to other cells by actin-based motility causing vasculitis throughout the process.
What are the 2 arthropod vectors of Rocky mountain spotted fever? What are their geographical distributions?
Dermacentor andersoni: rocky mountain states
Dermacentor variabilis: east of the rocky mountain states
How would you treat someone with suspected rocky mountain spotted fever? Pregnant with suscpected RMSF?
Treatment should be empiric with doxycycline, based on clinical suspicion and epidemiology. Should be empiric because delaying administration of antibiotics can increase risk of mortality.
If pregnant give chloramphenical because doxycycline is contraindicated with pregnancy
How are rickettsial diseases most often diagnosed?
With direct fluorescent antibody or immunoperoxidase of skin biopsy (the bacteria can be found in the endothelium of skin)
Name and describe the pathogen that causes lyme disease. What is the vector for this disease?
Borrelia burgdorferi: gram negative spirochete
Vector: Ixodes ticks
Describe the epidemiology of lyme disease
Humans are accidental hosts of B. burgdorferi. The spirochetes reservoirs are white tailed deer (preferred) and the white-footed mouse. Feeding of an Ixodes tick on an infected animal and subsequent feeding on humans can pass the bacteria on
How long must an Ixodes tick be attached to a host to infect them with Borrelia burgdorferi?
At least 24-36 hours
What is the tell-tale symptom of early lyme disease?
Erythema migrans: bulls’ eye rash
How is lyme disease diagnosed?
Through 2-tiered testing:
1) ELISA screening of IgM and IgG: highly sensitive but not specific
2) Western blotting: highly specific but not sensitive
What is babesiosis? How is it related to lyme disease?
Infection of red blood cells by a parasite called Babesia microti. Babesiosis hase the same epidemiology as lyme disease: same vector and reservoir
What is the spectrum of symptoms of babesiosis? Since the parasite infects red blood cells what 2 types of disease would you expect it to cause? What are 2 antibiotic combinations used to treat babesiosis?
Spectrum of disease can range from asymptomatic to life-threatening.
Complications include: anemia and thrombocytopenia
Treatment: clindamycin/quinine or atovaquone/azithromycin
What disease might babesiosis be confused with when performing a blood smear diagnosis?
Malaria because both parasites can be found inside the red blood cells
