Ectoparasites

Question 1

Black Widow

Morphology/Epidemiology

Answer 1

• 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

Question 2

Black Widow

Clinical Characteristics

Answer 2

• 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%

Question 3

Black Widow

Treatment

Answer 3

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

Question 4

Brown Recluse

Morphology/Epidemiology

Answer 4

• 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

Question 5

Brown Recluse

Clinical Characteristics

Answer 5

• 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

Question 6

Brown Recluse

Treatment

Answer 6

• 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

Question 7

Scorpions

Morphology/Epidemiology

Answer 7

• 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

Question 8

Scorpions

Clinical Characteristics

Answer 8

• 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

Question 9

Scorpions

Treatment

Answer 9

• 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

Question 10

Itch Mite (Scabies)

Morphology/Epidemiology

Answer 10

• 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

Question 11

Itch Mite (Scabies)

Clinical Characteristics

Answer 11

• 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

Question 12

Itch Mite (Scabies)

Treatment

Answer 12

• 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

Question 13

Chigger Mites

Morphology/Epidemiology

Answer 13

• 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

Question 14

Chigger Mites

Clinical Characteristics

Answer 14

• 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

Question 15

Chigger Mites

Treatment

Answer 15

Symptomatic including antipruritics, antihistamines, and steroid creams

Use of DEET in insect infested areas may prevent human infestation

Question 16

Head Louse

Morphology/Epidemiology

Answer 16

• 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

Question 17

Head Louse

Clinical Characteristics

Answer 17

• 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

Question 18

Head Louse

Treatment

Answer 18

• 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

Question 19

Bed Bugs

Morphology/Epidemiology

Answer 19

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 2^nd half of the 20th century but they are becoming increasingly more common in the US, Canada and the UK

Question 20

Bed Bugs

Clinical Characteristics

Answer 20

• 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

Question 21

Bed Bugs

Treatment

Answer 21

Lesions should be managed symptomatically w/ topical corticosteroids and/or oral antihistamines