Exam #8: Parasitic/ Arthropod Skin, Soft Tissue, & Muscle Infections Flashcards
What is Leshmaniasis?
Protozoa that is transmitted by the bite of an infected female sand fly
- Canines & rodents are important reservoirs
Describe the lifecycle of Leishmaniasis.
- Infected female sand flies deliver extracellular flagellated promastigote forms of the parasite
- Parasite is rapidly phagocytosed by macrophages & monocytes
- In macrophages & monocytes, Leshmania differentiate into non-motile amastigote forms
- Amastigote form replicates & persists in the host
What are the three major Leishmaniasis-associated diseases in man, what specific species cause them?
1) Cutaneous leishmaniasis= L. major, tropica, & mexicana
2) Mucocutaneous leishmaniasis= L. braziliensis
3) Visceral leishmaniasis= L. donovani, infantum, and chagasi
What are the symptoms of cutaneous Leishmaniasis?
- Raised , dry, crusty lesion at site where parasites were inoculated.
- Lesion slowly enlarges and then ulcerates.
- Self limiting infection.
What are the symptoms of mucocutaneous Leishmaniasis? How is it treated?
- Infection initially presents as a typical cutaneous lesion.
- Months to years after resolution of the initial infection, ulcerative lesions develop, typically in the nasal mucosa and septum
*Note that within infected individuals, only intracellular (found EXCLUSIVELY in mononuclear phagocytes) forms are found; thus, antibodies offer little or no protection. Cell-mediated immunity is important. Treatment is with heavy metal compounds that are considerably toxic.
What is Onchocerciasis?
River Blindness
What causes Onchocerciasis?
Onchocerca volvulus, which is a filarial nematode
Describe the lifecycle of Onchocerca volvulus.
- Infected black fly bites human
- Microfilariae are introduced via the open wound & mate
- Adult worms exist knotted together in subcutaneous nodules
- Microfilariae escape from the nodules & migrate through subuctaneous tissue
- The inflammatory reaction to these migrating microfilariae leads to an intense pruritic rash
- In the eye, this leads to sclerosing keratitis resulting in a hardening inflammation of the cornea and blindeness
*Note that transmission is through INFECTED BLACK FLIES
What is Onchocerciasis most endemic?
1) Africa
2) Central & South America
What are the symptoms of Onchocerciasis?
- Intense pruritic rash (itching) from immune response to microfilariae
- Blindness may take years to develop & occurs in 5-10% of infected individuals
*Note that the itching accompanied by this rash is so bad that suicide is NOT uncommon
How is Onchocerciasis diagnosed?
Visualizing microfilariae from skin snips
How is Onchocerciasis treated?
Ivermectin, which appears to interfere with the release of microfilariae
What is Filariasis? What causes Filariasis?
Filariasis is caused by Mansonella sp., a filarial nematode
Where is mansonella endemic?
M. streptocerca- Central Africa
M. perstans- Africa, Caribbean, South America
M. ozzardi- Central & South America + Caribbean
What is the lifecycle of mansonella?
Microfilaria are transmitted by the bite of infected midges
What are the symptoms of mansonella infection?
- Cutaneous itching
- Joint pain
What is Dracunculiasis?
- A nematode infestation of the skin that is endemic to Africa
- The causative organism is Dracunculus medinensis, which is a tissue dwelling nematode that grows to be 50-100cm in length
Describe the lifecycle of Dracunculus medinesis.
- Larvae are released from ingested copepods in the small intestine
- Larvae penetrate the intestinal & abdominal wall, entering the connective & subcutaneous tissue
- Larvae develop into adults
- Gravid females migrate to the extremities & trunk
- It is the presence of these gravid females that leads to the development of indurated papules the eventually ulcerate
How do humans acquire Dracunculus medinesis?
- Swallowing microscopic freshwater copepods (crustaceans) that are infected with larval forms of the worm
- I.e. contaminated drinking water
How has Dracunculosis been prevented?
Preventing water contamination
What is the treatment for Dracunculosis?
Wind the worm out on a stick
*Note that it is important NOT to break to he worm during removal; severe anaphylactic reactions have been reported in response to disintegrating adult worms
What is cutaneous larva migrans?
Hookworms of dogs and cats infecting humans
How is cutaneous larva migrans transmitted?
- Penetration skin of humans
- Fail to get into circulation; rather, migrate in subcutaneous tissue and die, causing an inflammatory reaction
*Happens in the caribbean with wild dogs and cats
What are the symptoms of cutaneous larva migrans?
Erythematous, pruritic lesions usually on the feet & legs
“Creeping eruption” is pathognomonic for cutaneous larval migrans
What is Scabies?
The most common superficial dermatitis seen in the US, caused by “Sarcoptes scabiei”
Describe the lifecycle of Scabies.
- Infection begins when a female mites is transferred from an infected individual via direct contact
- Mite burrows into the skin, laying eggs all the while
- Larvae hatch, leave the burrow, & establish new burrows
- Males & females mate & produce more eggs
Where are Scabies mites most commonly found?
Webbing & sides of fingers, later spreading to the wrists, elbows, and the trunk
What are the symptoms of Scabies?
- Itching in the webbing & sides of fingers, later spreading to the wrists, elbows, and the trunk
- Lesions appear as short, serpentine, slightly raised cutaneous tracts
*Note that typical infection only involve s 1/2-12 female mites
What is Norwegian or crusted Scabies?
Scabies hyperinfection that presents as crusted scabies; this is caused by infestation with thousands of mites
How is Scabies diagnosed?
- Direct visualization of mites
- Microscopic evaluation of skin scrapings
*Mites or eggs confirms diagnosis
How is Scabies treated?
- Topical formula
- Recommended that all members of a household are treated
- Aggressive cleaning of clothing & linens
Describe the characeristics of lice.
Lice or “Pediculosis” is an obligate blood-feeding ectoparasites
- Wingless
- Six-legged
- Flattened insects
What are the three species of lice that infect humans?
Body louse= Pediculus humans
Head louse= P. humanus capitis
Crab louse= Phthirus pubis
*Note that the crab louse has 2nd & 3rd sets of legs that are clawed, resembling crabs
What is the presentation of lice?
The usual characteristics of all infestation types is intense itching with pruritic reddened papules
What two species of lice are “sedentary?”
Head
Crab
*Thus, the body louse is mobile; it remains on clothing and moves from clothes to body for a meal–then goes back to the clothing
Describe the lifecycle of lice.
- Female lice lay eggs (nits) that attach to hair shafts
- Eggs hatch
*The body louse is different; it resides in clothing & is mobile. Eggs around found in the seams of infested garments
How is lice diagnosed?
Identification of lice or eggs in hair or in seams of clothing
What are nits?
Louse eggs that attach to hair
How is lice treated?
Low dose insecticides in dusts, shampoos, lotions, and creams
- Aggressive washing of bedding and clothing (hot water)
- Nit combs
What is Myiasis?
Myiasis is the term used to describe the infestation of tissue by the larvae i.e. maggots of flies
Describe the lifecycle of the Human Botfly.
- Adult flies capture blood sucking athropods, lay their fly eggs on the abdomens of the arthropod, and then release the arthropod
- When the arthropod with fly eggs lands on the mammal, eggs hatch, releasing larvae onto the skin & into the wound created by the bite
- Eggs grow into maggots
What species of Botfly infects humans?
Dermatobia hominis
What is Trichinosis?
Trichinosis or Trichinellosis is a nematode infection caused by the ingestion of infected meat, mainly pork
- Larvae from infected females encysts in muscle causing tissue specific symptoms
- GI symptoms include diarrhea, abdominal pain, and vomiting
What organism causes Trichinosis?
Trichinella spiralis, a nematode associated with eating under prepared meat (esp. pork)
Describe the lifecycle & transmission of Trichinella spiralis.
- Infection begins following the ingestion of infected meat (pork)
- Within the small intestine, larvae excyst and develop into adults
- Fertilized females release infectious larvae that penetrate the mucosa, enter the bloodstream, and encyst with muscles
What is a nurse cell?
Encysted larvae in muscle cells
How is Trichinosis diagnosed?
- Eosinophilia
- Elevated muscle enzymes
- Antibody testing
- Observation of encysted larvae in muscle biopsy= definitive diagnosis
What is Loiasis?
- Colloquially, the “eye worm”
- Filarial nematode infestation seen in Africa that can be found in subcutaneous tissues & peripheral blood
- Has a tendency to travel to the eye
What causes Loiasis?
Loa Loa
How is Loa Loa transmitted?
Bite of infected Mango flies
What are the symptoms of Loiasis?
Calabar swellings= inflammatory response to subcutaneous adults that is characterized by 10-20cm non-erythematous angioedematous swellings that last for a few days
*Note that findings worms in the conjunctiva is common; these must be surgically removed
What is Paragonimus westermani?
Lung Fluke
Where is the Lung Fluke endemic?
Asia & South America
Describe the presentation of the Lung Fluke.
- Masquerades as TB
- Patient presents with “Rust colored sputum”
*Note that “rust colored” sputum is also associated with S. pneumoniae–>pneumonia
