Tick Borne Infections

Question 1

Describe Ricketssial pathogens

Answer 1

Small, pleomorphic gram negative coccobacilli that are obligate intracellular bacteria. Arthropod intermediate host. No flagellar motility but have actin-based motility

Question 2

What are the ricketssial pathogens and what diseases do they cause?

Answer 2

Ricketssia spp.: spotted fevers and typhus

Orientia tsutsugamushi: scrub typhus

Question 3

Scrub (bush typhus) is a ricketssial diease. What is the causal organism and its vector and reservoir?

Answer 3

Caused by orientia tsutsugamushi. Vector: mites (chiggers). Reservoir: rodents

Question 4

What are the distinguishing features of scrub typhus?

Answer 4

Morbilliform rash, hemorrhaging and intravascular coagulation, vasculitis

Question 5

There are 2 types of typhus. What are they and what are the 4 ways in which they differ?

Answer 5

Epidemic and endemic typhus. They differ by: causal pathogen, transmission mode, vector and reservoir

Question 6

What cause epidemic typhus? How is it transmitted? What is its vector and reservoir?

Answer 6

Ricketssia prowazekii, it is transmitted form person to person
Its vector is lice and its reservoir is humans

Question 7

What causes endemic typhus? How is it transmitted? What is its vector and reservoir?

Answer 7

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.

Question 8

What distinguishes epidemic typhus from endemic typhus? How are they similar

Answer 8

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

Question 9

How is the rash progression of spotted fevers different from typhus?

Answer 9

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

Question 10

How is Ricketssia spread to humans?

Answer 10

Humans are an accidental host of Ricketssia. Ricketssia is spread to humans through ticks during a blood meal

Question 11

How are ticks infected with Ricketssia?

Answer 11

Ricketssia-free ticks must feed on bacteremic hosts such as mice, rats, rabbits, squirrels

Question 12

How does Ricketssia cause vasculitis?

Answer 12

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.

Question 13

What are the 2 arthropod vectors of Rocky mountain spotted fever? What are their geographical distributions?

Answer 13

Dermacentor andersoni: rocky mountain states

Dermacentor variabilis: east of the rocky mountain states

Question 14

How would you treat someone with suspected rocky mountain spotted fever? Pregnant with suscpected RMSF?

Answer 14

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

Question 15

How are rickettsial diseases most often diagnosed?

Answer 15

With direct fluorescent antibody or immunoperoxidase of skin biopsy (the bacteria can be found in the endothelium of skin)

Question 16

Name and describe the pathogen that causes lyme disease. What is the vector for this disease?

Answer 16

Borrelia burgdorferi: gram negative spirochete

Vector: Ixodes ticks

Question 17

Describe the epidemiology of lyme disease

Answer 17

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

Question 18

How long must an Ixodes tick be attached to a host to infect them with Borrelia burgdorferi?

Answer 18

At least 24-36 hours

Question 19

What is the tell-tale symptom of early lyme disease?

Answer 19

Erythema migrans: bulls’ eye rash

Question 20

How is lyme disease diagnosed?

Answer 20

Through 2-tiered testing:

1) ELISA screening of IgM and IgG: highly sensitive but not specific
2) Western blotting: highly specific but not sensitive

Question 21

What is babesiosis? How is it related to lyme disease?

Answer 21

Infection of red blood cells by a parasite called Babesia microti. Babesiosis hase the same epidemiology as lyme disease: same vector and reservoir

Question 22

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?

Answer 22

Spectrum of disease can range from asymptomatic to life-threatening.
Complications include: anemia and thrombocytopenia
Treatment: clindamycin/quinine or atovaquone/azithromycin

Question 23

What disease might babesiosis be confused with when performing a blood smear diagnosis?

Answer 23

Malaria because both parasites can be found inside the red blood cells