6 Ectoparasitic Infections

Question 1

Burrowing mite that is the most serious of the mites

Answer 1

Sarcoptes scabiei

Close relatives of ticks

Question 2

Ectoparasite that leads to scabies, crusted scabies, mange, seven-year-itch, etc

Answer 2

Sarcoptes scabiei

Question 3

Morphology of Sarcoptes scabiei

Answer 3

Small mite with SHORT legs

Question 4

What does the female sarcoptes scabiei life cycle look like?

Answer 4

Fertilized on the skin surface

Burrows into the epidermis

Female completes the life cycle in 5 weeks, dies in the burrow

Question 5

What does the male sarcoptes scabiei life cycle look like?

Answer 5

Shorter life span

Remains on the skin surface or produces a shallow burrow

Question 6

Where does the sarcoptes scabiei mite lay its eggs?

Answer 6

Under the skin

Larva emerges from the egg after 4 days incubation

Adult mite develops 2 weeks after hatching

Question 7

Main clinical manifestation of scabies is …

Answer 7

PRURITIS

The first time someone is infested with S. scabiei, sensitization (allergic response) takes weeks to develop

In reinfections, pruritis can develop within 24 hours

Question 8

_______ causes the majority of clinical issues with scabies

Answer 8

Burrowing

Causes an intensely pruritic eruption that is worse at night

Question 9

What is Crusted (Norwegian) Scabies?

Answer 9

Incubation period of ~1 month

Crusted scaling lesions that are intensely pruritic

Observed readily in HIV patients

Lesions are teeming with hundreds of thousands of mites

Question 10

What is pediatric scabies?

Answer 10

Similar to norwegian scabies but lesions may be blood filled

Question 11

Scabies is usually transmitted by…

Answer 11

Direct person to person contact

In adults, it is likely an STI

Can be zoonotic (rarely)

Found in crowded living conditions

Question 12

How to identify scabies

Answer 12

Apply mineral oil, scrape lesion and visualize microscopically

Looking for whole mite or mite parts, eggs, or fecal pellets in burrows

Question 13

What is the treatment for scabies?

Answer 13

5% permethrin cream (single application) applied over all body below neck, washed off only after 8-14 hours

Can also use Ivermectin but it does not kill eggs

Clinical findings should subside within 2 weeks (if not, retreat)

Question 14

Besides the medical treatments, what else should you tell scabies patients to do?

Answer 14

Warn of issues with absorption of topicals

Thoroughly wash all bedding and clothes in hot water

Examine all sexual partners for signs of infestation

Question 15

What is the organism responsible for “crabs”

Answer 15

Phthirus pubis - pubic lice

Dwells on pubic hair

Nit (eggs) cemented to hair, adults bite and feed in pubic area

Question 16

Transmission of phthirus pubis is via…

Answer 16

Sexual contact or contaminated bedding

ID by visualizing louse or nit

Question 17

How do you treat phthirus pubis?

Answer 17

Permethrin

Question 18

How is Pediculus humanus different from Phthirus pubis?

Answer 18

Longer, shorter legs

Two different species
• P. humanus capitis = head louse
•P. humanus humanus = body louse

Question 19

Vector for epidemic typhus

Answer 19

Pediculus humanus

Question 20

What does the life cycle for Pediculus humanus look like?

Answer 20

Nit is cemented to a fiber in clothing or in human hair

Egg-to-egg cycle takes about 3 weeks

Question 21

What is the pathogenicity of pediculosis?

Answer 21

Bite irritation (blood sucking parasites)

“vagabond’s disease” as a result of years of infestation

Darkened, thickened skin

Question 22

How is P. humanus spread?

Answer 22

Easily

Especially in crowded conditions, conditions where clothing cannot be changed often

Question 23

Treatment for P. humanus

Answer 23

Permethrin

Many OTC treatments available

Question 24

What is the scientific name for the human flea?

Answer 24

Pulex irritans

Question 25

What does Pulex irritans look like?

Answer 25

1-4 mm in length Laterally compressed Short spikes on legs that allow attachment to host Parasites that absolutely need blood to survive

Question 26

Main manifestation of flea infestation is...

Answer 26

Rash During a blood meal, flea injects saliva, known to posses at least 15 substances which initiate allergic responses

Question 27

Treatment for pulex irritans

Answer 27

Cessation of scratching 1% hydrocortisone Antihistamines

Question 28

Rocky Mountain Spotted Fever is caused by what organism

Answer 28

Rickettsia rickettsii Gram negative obligate intracellular non-motile pleomorphic bacterium spread by ticks

Question 29

Rocky Mount Spotted Fever is a ______ borne disease

Answer 29

Tick-borne American dog tick Rocky Mountain wood tick BROWN DOG TICK**** - common species for spread in AZ

Question 30

When does RMSF most frequently occur?

Answer 30

April to October, with peak in June and July Varies based on vector species and climate

Question 31

First symptoms of RMSF begin _____ days after tick bite

Answer 31

2-14 days Bite is usually painless, organism invades endothelial cells that line blood vessels

Question 32

Early symptoms of RMSF are...

Answer 32

Non-specific: ``` Fever HA N/V Abdominal/muscle pain Lack of appetite Conjunctival infection ```

Question 33

What does the RMSF rash look like?

Answer 33

Two types: 1) small, flat pink non itchy spots on wrists, forearms, and ankles —> spreads to trunk, palms, and soles If present, 2-5 days post infection 2) RED to purple spotted petechial rash with pinpoint hemorrhages in up to 60%, usually after 6 days post infection

Question 34

The 2nd type of RMSF rash is a sign of

Answer 34

Late infection and severe disease Every attempt should be made to begin treatment before petechiae develop

Question 35

Diagnosis of RMSF is based on...

Answer 35

Clinical signs and symptoms and patient history Do NOT delay treatment while waiting for lab confirmation, as most successful if treatment is initiated within 5 days Gold standard is indirect immunofluorescence with a R. rickettsii antigen but organism is difficult to detect until the disease is in late stages

Question 36

Treatment for RMSF

Answer 36

Doxycycline If pregnant, chloramphenicol (but watch out for aplastic anemia)