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2014-12-16 04:50:22
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  1. What are the filarial worms and the disease they cause? (elephantiasis)
    • Wucheria bancrofti (elephantiasis / Bancroftian filariasis)
    • Brugia malayi (Brugian filariasis)
    • Loa loa (Loa filariasis)
    • Onchocerca volvulus (Onchocerciasis, river blindness)
    • ***Dracunculus medinensis (not a filarial worm)
  2. What is another name for blood/tissue dwelling nematodes
    Filarial worms
  3. general filarial worms - morphology, hosts, life cycle
    • morphology: long and threadlike morphology
    • reduced lips and buccal capsule
    • females are viviparous (produce microfilariae larvae - no eggs)
    • microfilariae are important diagnostic tools
    • sheathed worms: inhabit the blood
    • unsheathed worms inhabit the tissues
    • hosts: parasitize all classes of vertebrates (except fish)
    • life cycle: indirect (2+ hosts)
    • microfilariae survive in blood, but cannot develop
    • upon ingestion by arthropod, microfilariae -> rhabditiform larvae -> filariform larvae (infective)
    • filariform (L3) injected during bloodmeal, transforms into adult in human
  4. W. bancrofti and B. malayi- general morphology, size, location, offspring info
    • Adults are long, slender w/ smooth cuticle and rounded
    • male is 40mm long, tail is curved
    • female is 60-100mm long
    • adults live in major lymphatic ducts (tightly coiled)
    • females produce thousands of sheathed microfilariae (240-300um) - nuclei absent in tail
  5. W. bancrofti and B. malayi- life cycle (detail)
    • Microfilariae released into surrounding lymph (most end up in blood)
    • marked periodicity of microfilariae in blood (maximum # bwn 10p-2a)
    • vectors include Culex, Anopheles, Aedes, and Mansonia
    • after ingestion by vector microfilariae lose their sheath
    • become L1 (sausage stage) -> -> L3 (filariform larvae)
    • filariform larvae enter host during blood meal
    • worms settle in larger lymph vessels and mature
  6. define periodicity - why might it occur?
    • tendency for microfilariae to appear in blood during certain times of the day (as in Wuchereria bancrofti)
    • makes microfilariae available to vector 
    • sleep is associated with physiological factors (decreased temp, O2 tension, increased CO2, lower adrenal activity, etc)
    • *NOTE - dependent on circadian rhythm, not light/dark (AKA it can be reversed)
  7. W. bancrofti and B. malayi - pathogenesis
    • Individuals may have symptoms for 16 years
    • Filariasis depends greatly on immune system and inflammatory response of hosts
    • female can release microfilariae for up to 10 years!!
    • incubation phase: time between infection and appearance of microfilarie in blood
    • largely symptomless, may have mild fever
    • acute inflammatory phase: female worms start releasing microfilariae
    • adult females block lymph vessels and glands, resulting in edema
    • intense lymphatic inflammation most affects lower half of body
    • chills, fever, and toxemia
    • affected areas become swollen and painful
    • obstructive phase: 
    • lymph varcies, chyluria (lymph in urine), hydrocele (fluid accumulation around testicles), and elephantiasis
  8. describe the hydrocele in detail
    • Result of W. bancrofti obstructive phase
    • plugging of inguinal lymphatic canals leads to fluid filled front sides of testicle and epididymis in scrotum
    • not usually painful, but uncomfortable due to increased size
  9. W. bancrofti and B. malayi- symptoms of elephantiasis
    • skin becomes thickened and cracked, invasive bacteria and fungi complicate the matter!
    • *NOTE - microfilariae are not usually present
    • Elephantiasis is a result of complex immune responses (long duration) and repeated infection
    • <10% of infected population have elephantiasis
    • 1-time infection will likely result in localized edema, and painful inflammation, NOT elephantiasis
  10. W. bancrofti and B. malayi- diagnosis, treatment, prevention/control
    • diagnosis: demonstration of microfilariae in blood (take periodicity into account)
    • ultrasonography used to detect movement and noises caused by adult worm movement
    • X-Ray exams can reveal calcified worms
    • treatment: hetrazan kills microfilariae and adults
    • metronidazole may also be effective
    • swollen limbs treated with pressure bandages
    • surgical removal of elephantoid tissue
    • prevention: protection against mosquito bites (repellent, netting, etc)
  11. Differences between B. malayi and W. bancrofti
    • tail of B. malayi contain two terminal nuclei (absent in W. bancrofti)
    • Brugian filariasis is not as widely distributed as bancrofitan filariasis
  12. L. loa - geography, disease name, AKA, location, vector, size
    • geography: rain forests of Central and West Africa
    • disease: Loa filariasis
    • AKA: eye worm
    • Location: subcutaneous tissue in ANY part of the body
    • vector: Chrysops flies ("deer", "horse")
    • size: males 3.2cm, females 5.5cm 
    • *NOTE - known to be highly visible during development
  13. L. loa - life cycle/infection
    • Adults mate, produce sheathed microfilariae w/ blunt tail and nuclei extending to the tip of the tail
    • periodicity bewteen 10a and 2p
    • after vector (Chrysops) ingests microfilariae, L1 develops into L3 filariform (infective)
    • migrating adult worms near skin surface cause most pathological problems
  14. L. loa - pathology
    • migrating adult worms near skin surface cause most pathological problems
    • worms often appear around eye where they can be easily seen and extracted before they damage the conjunctiva
    • calabar swelling: immune rxn to migrating worms, cause enlargements of chest, groin and eye (very itchy and painful)
    • *NOTE - swelling caused by worm aggregation
  15. L. loa - diagnosis, treatment, control/prevention
    • diagnosis: usually doesn't occur until a year after infection
    • calabar swellings occurs when adults are stationary
    • adults visible in conjunctiva
    • demonstration of microfilariae in blood
    • treatment: surgical removal of swellings is recommeded
    • chemotherapy similar to bancroftian filariasis
    • control: control of deer flies is difficult, they breed in swampy forests
    • prevention: avoid bites of deerflies (wearing long pants, sleeping in well-screened areas)
  16. define prepatent period
    the period of time between infection and diagnosis
  17. O. volvulus - disease, geography, infection rates, size, vector
    • River blindness (Onchocerciasis)
    • distributed in much of the world (mostly Africa, not Asia)
    • >30 million infected in Africa alone
    • adults up to 50cm long, become surrounded by fibrotic tissue (appears as nodule)
    • vector: Simulium (black fly)
  18. O. volvulus - life cycle/infection
    • Female worms produce microfilariae that remain in the skin
    • Similium infected when it feeds on human (L1 -> L3)
    • L3 larvae enter body during Similium bite, move to subcutaneous tissues
    • larvae become encapsulated in nodules and mature into adults (~1 year)
  19. What is the big difference between O. volvulus and other filarial infections?
    • O. volvulus microfilariae cause most of the problems, not adults!
    • microfilariae enter the eye and die, causing blindness
  20. Describe symptoms of O. volvulus
    • *NOTE - microfilariae cause the problems!
    • blindness caused by death of microfilariae in eyes (up to 40% of population in endemic areas)
    • ocular lesions, keratitis, glaucoma, cataract, blindness
    • death of microfilariae in skin results in severe dermatitis and depigmentation
    • disfigurment caused by depigmentation + adult worm nodules
    • severe itchiness of nodules can lead to suicide!
    • light infections can be asymptomatic or have mild pruritis (itching)
    • reactions to dead microfilariae (long term) results in destruction of elastic tissues, hanging groin (folds around scrotum)
  21. Why is O. volvulus disease called "river blindness"?
    • Microfilariae die in eyes, causing blindness
    • Simulium flies (vector) breed in fast flowing rivers (high oxygen levels)
    • hense - river blindness
  22. O. volvulus - diagnosis, treatment, prevention/control
    • diagnosis: skin snip in drop of saline (microfilariae will leave skin within seconds)
    • treatment: DEC kills microfilariae, but causes Mazzotti reaction (strong allergic rxn) and can result in anaphylactic shock
    • Ivermecten does not appear to induce this rxn
    • *NOTE - neither drug kills adults
    • Only way to treat adult is nodulectomy (prevents microfilariae production)
    • Prevention/control: vector control (spraying breading grounds of black fly, clearing vegetation around village areas)
  23. D. medinensis - AKA, disease name, history, geography, size, location
    • AKA: guinea worm, fiery serpent
    • disease: dracunculiasis
    • history: mentioned in ancient writings
    • geography: Asia, Middle Easy, Northern Africa
    • *NOTE - D. insignis (similar) found in carnivores of NA (not humans)
    • size: females - 1m in length, only 2mm in diameter
    • location: found just under skin of human host (legs, ankles, feet, are common)
  24. D. medinensis - life cycle
    • *NOTE - unusual
    • female worms found in skin of host
    • as she becomes gravid her body fills with embryos
    • female's body wall ruptures and worms are released into host skin
    • causes intense allergic rxn, extreme discomfort, and nodule (papule) on skin
    • Papule eventually ulcerates, providing escape for juvenile worms and visible adult female
    • *NOTE - hosts usually seek out water to alleviate symptoms, which liberates juveniles into water
    • juveniles are eaten by copepod
    • humans are infected when the drink water containing infected copepod
    • juveniles migrate from intestinal tract through abdomen into subcutaneous tissues (become adults)
    • males die after copulating with females
    • females migrate to the skin and produce juveniles
  25. D. medinensis - symptoms, treatment
    • symptoms: sores produced by female worms can be infected with bacteria
    • some worms become encapsulated in tissues, arthritis may result (based on location)
    • no immunity results in constant reinfection
    • treatment: several drugs
    • mostly treated by removal of female worm once blister breaks (match stick removal)