Ectoparasites Flashcards
1
Q
Black Widow
Morphology/Epidemiology
A
- Globular, shiny black abdomen with characteristic orange or red hourglass marking on the ventral surface
- Females are 4 to 14 mm in length
- Common in southern US and found throughout temperate and tropical regions of the world
- Frequent wood piles, brush cellars, logs and privies
- Bites are most common on buttocks, genitalia and extremities
- Bite of the female delivers a potent peripheral neurotoxin
2
Q
Black Widow
Clinical Characteristics
A
- Initial findings include sharp pain @ bite site w/ redness, swelling, and burning
- Systemic sx occur w/in 1 hour and include cramps, nausea, vomiting and intestinal spasms
- Sx start to abate in 48 hours but paralysis and coma may precede cardiac arrest
- Small children and weakened adults are the most susceptible to severe disease
- Mortality estimates at ~ 4%
3
Q
Black Widow
Treatment
A
Specific anti-venom is available and should be administered shortly after the bite
Anti-venom prepared in horses and carries risk associated w/ heterologous serum including serum sickness and anaphylaxis
4
Q
Brown Recluse
Morphology/Epidemiology
A
- Yellow or brown w/ long legs, 5 to 10mm in length
- Distinguishing marks include a dark fiddle or violin shape on the dorsal side of the abdomen
- Both the male and female inject a potent necrotoxin that also has hemolytic activity
- Spider is found in south and western US and in South America
5
Q
Brown Recluse
Clinical Characteristics
A
- Bite is painless
- Followed by itching, burning and swelling after several hours
- Fluid-filled vesicle or bleb frequently forms @ site of the bite
- Bleb sloughs w/in 4 days ⇒ ulcer
- Ulcer may necrotize & necrosis may spread for weeks to months
-
± Intravascular coagulation, cardiac or renal failure
- Hemolytic syndrome more common w/ bite of the spider found in South America
- Dx is not straightforward but usually based on lesion appearance & probability of the bite
6
Q
Brown Recluse
Treatment
A
- Depends on severity
- No treatment → wound cleansing and abx to prevent secondary bacterial infection
- ± Debridement and skin grafting for lesions that have not healed after 6-8 weeks
- Anti-venom is used in South America but not available here
7
Q
Scorpions
Morphology/Epidemiology
A
- Elongated abdomen w/ pincer like claws extending from the anterior area
- Abdomen tapers to a curved, hollow stinger
- Both male and female use the stinger to inject venom when threatened
- Dangerous scorpions are found in southwestern US, Mexico, and parts of South America particularly Venezuela
- Nocturnal and hide under rocks and logs during the day
- Children under 5 most susceptible to severe disease resulting from a sting
8
Q
Scorpions
Clinical Characteristics
A
- Scorpions produce a neurotoxin and a hemolytic toxin
- Hemolytic toxin ⇒ local reactions like pain, burning, tingling, and numbness
- Neurotoxin ⇒ systemic effects such as drooling, sweating, muscle spasm, chills, difficulty speaking, seizures
- Death may result from pulmonary edema or cardiac arrest
9
Q
Scorpions
Treatment
A
- Local sx, mostly supportive for pain
- Systemic sx in young children are serious and treated supportively for shock
- Anti-venom available but only effective if administered shortly after the sting
10
Q
Itch Mite (Scabies)
Morphology/Epidemiology
A
- Adult mites are very small (300-400microns) w/ a sac-like body and 4 pairs of legs
- Obligate parasite of animals and humans
- Can survive about 48 hours when it is not living on a host
- Spread by direct contact or contact w/ contaminated objects (ie, clothing), and sexual transmission
- It frequently causes outbreaks in crowded living conditions such as prisons, barracks, nursing homes
11
Q
Itch Mite (Scabies)
Clinical Characteristics
A
- Adult female mite burrows into the skin where she lays her eggs
- Larval and nymph stages hatch and burrow into the skin
- Preferred sites are interdigital folds, folds in the wrist and elbow and inguinal regions
- Adult female mite is usually located at the terminal portion of the burrow
- Can live up to 1 month on the host
- Mites and their secretions cause intense itching
- Itching ⇒ scratching ⇒ excoriation and secondary bacterial infections
12
Q
Itch Mite (Scabies)
Treatment
A
- Several total body applications of a 5% permethrin cream used
- Thorough cleansing of the environment must be done to prevent a recurrence
- Prevention is by good personal hygiene
13
Q
Chigger Mites
Morphology/Epidemiology
A
- Chiggers are the larvae of specific mite family, Prostigmata
- Very small (05mm) and look like a reddish dot
- Routinely found on grasses and bushes
- Attach to skin at sites where clothing is tight such as wrists, ankles, groin, waistline
- Inject saliva w/ enzyme that breaks down cells, feed on tissue fluid, fall off skin and molt into the nymph form
- In North America, chiggers do not spread disease but in Asia they may carry scrubtyphus
14
Q
Chigger Mites
Clinical Characteristics
A
- Saliva from the chigger injected into skin during feeding causes intense itching and a dermatitis
- Lesions appear as small red marks that progress to a papule that takes weeks to heal
- Usually concentrated to waist, ankles, neck and armpits
- Intense scratching can lead to bacterial infections of the skin
15
Q
Chigger Mites
Treatment
A
Symptomatic including antipruritics, antihistamines, and steroid creams
Use of DEET in insect infested areas may prevent human infestation
16
Q
Head Louse
Morphology/Epidemiology
A
- Elongated, flat, wingless insects w/ three pairs of legs and mouthpieces used to suck blood
- Outbreaks of head lice frequently reported in schools, camps and daycares
- Live on the hair shaft and move to the scalp to take a bloodmeal
- Transmitted by direct contact and sharing contaminated articles such as hairbrushes
- The nit (egg) contains a developing larva
- It may be removed by combing w/ a fine tooth comb
17
Q
Head Louse
Clinical Characteristics
A
- Associated w/ intense itching
- Nits (eggs) are white, round objects found attached to the hair shaft
- Can be easily mistaken for dandruff
- No infectious agents are transmitted by the head louse in contrast to the body louse which may transmit typhus or relapsing fever
18
Q
Head Louse
Treatment
A
- Gamma benzene hexachloride (lindane) applied to hair 2-3x during the course of a week
- Nit combing may be recommended as an adjunct treatment
- Lice may survive on inanimate objects for 2 weeks
- Bedding, clothing, hairbrushes must all be treated w/ the chemical agent or washed and dried using high heat
- Screening for head lice is frequently done in schools
- Prohibiting infected students in schools until treatment is completed is controversial
19
Q
Bed Bugs
Morphology/Epidemiology
A
C. lectularius
- Wingless red/brown insect
- Grows up to 7mm in length
- Lifespan of 4 months to 1 year
- Hide in cracks and crevices of wood and fabric – commonly mattresses and headboards
- Emerge during the night to feed
- Humans are their preferred host
- Common bedbug is found worldwide
- Infestations are common in developing countries particularly under crowded and unsanitary living conditions
- Became rare in the US in the 2nd half of the 20th century but they are becoming increasingly more common in the US, Canada and the UK
20
Q
Bed Bugs
Clinical Characteristics
A
- Bedbug injects saliva into the blood stream of their host to thin the blood and prevent coagulation
- Saliva causes the clinical manifestations of the bed bug bites
- Small clusters of extremely pruritic, erythematous papules or wheals that represent repeated feedings by the same bug
21
Q
Bed Bugs
Treatment
A
Lesions should be managed symptomatically w/ topical corticosteroids and/or oral antihistamines
