SUBCUTANEOUS FILARIARIS Flashcards
What is the common name of loa loa?
African eye worm
Where is loasis endemic?
Central and West Africa
What is the habitat of loa loa?
Adult worms: subcutaneous tissues & often subconjunctival tissue.
Microfilaria: peripheral blood during the day (diurnal periodicity).
*Occasionally M.f have been demonstrated in urine, sputum & even CSF.
Describe the Morphology of loa loa
Adult Worm
*Is thin & transparent, measuring about 30–70 mm in length.
*They have a life span of 4–17 years
Microfilaria
Mf are sheathed
Briefly describe the life cycle of loa loa
*Is completed in 2 hosts.
*Definitive host: Man
*Intermediate host: Day biting flies of the genus Chrysops (mango flies) such as C. dimidiata, C. silacea & other species) .
①In the vector M.f develop into the infective third-stage larvae.
➁Transmitted to man through the bite of infected Chrysops during their blood meal.
③Infective larvae enter the skin then molt to develop into adult worms which migrate to subcut tissues.
④The female worm after being fertilized by males produce sheathed M.f that circulate in the peripheral blood
⑤The M.f are ingested by Chrysops during its blood meal.
⑥They cast off their sheaths, penetrate the stomach wall to reach thoracic muscles where they develop into infective larvae.
⊛Devt in chrysops is completed in about 10 days
How does loa loa manifest clinically？
Disease is produced by the adult worm in humans. loa filariasis is asymptomatic in many cases. The incubation period is on an average 3-4 years.
①Skin lesions
・Consists of calabar or fugitive swelling
Swellings are non erythematous & usually one develops at a time.
・Migrating adult worms cause oedema of subcutaneous tissues which disappear in 2-3 days.
・Wrist joints or knee joints are most frequently affected. Worms not usually present in the swellings
⓶Ocular lesions
・Conjunctival granuloma: present as solitary or multiple small nodules (2mm)caused by migrating adult worms in the sub-conjunctival tissues.
・Oedema of the eyelid:painless condition frequently accompanied by itching.
・Proptosis or ‘bulge eye’ caused by the edema of the orbital cellular tissue.
It is painless & of rapid onset frequently associated with itching
③Other complications:
・Include recurrence of swellings, endomyocardial fibrosis, retinopathy, encephalopathy, neuropathy & arthritis.
Meningoencephalopathy is a severe & often fatal complications of infection
Treatment of loasis
①Diethylcarbamazine(DEC) is the drug of choice & effective against both the adult and the microfilarial forms.
⓶Simultaneous administration of corticosteroids reduces allergic reactions.
③Ivermectin or albendazole are effective in reducing microfilarial loads.
④Surgical removal of the adult worms is rarely done
What about Onchocerca vovulus?
Causesonchocerciasisor ‘River blindness’
It also causescutaneous filariasis.
It also shares an endosymbiotic relationship with bacteriaWolbachia which in its absence ,larval devt is disrupted.
Onchocerca volvulus habitat:
Adult worms: subcutaneous connective tissue of infected persons.
Microfilaria: Are found typically in the skin & subcutaneous lymphatics in the vicinity of parent worms.
May also be found in the conjunctiva & rarely in peripheral blood.
Onchocerca volvulus morphology:
①Adult worm
⊛Are whitish, opalescent & transparent with transverse striations on the cuticle.
⊛The posterior end is curved hence the name Onchocerca meaning ‘curved tail’.
⊛Male worm is smaller than the female with posterior end coiled ventrally & also has 2 spicules of unequal length.
⊛The worms usually live 10 or more years in their host
⓶Microfilaria
⊛Anterior end is slightly enlarged, & tail is pointed.
⊛Both the anterior and posterior ends are nucleus free
Summarize the life cycle of Onchocerca volvulus:
*life cycle is completed in 2 hosts.
*Definitive host: Humans(only definitive host).
*Intermediate hosts: Day-biting female black flies of the genus Simulium (black flies). The vector species breed in fast-flowing rivers
①Humans get infected via injection of infective larva into the skin by the bite of female black fly.
⓶Larvae enter the skin through the punctured wound, migrate to the subcut tissue where they molt & develop into adult worms.
③They induce the formation of fibrous nodule in which they remain encapsulated
④Female worms after being fertilized by males produce unsheathed microfilariae.
⑤M.f migrate out of the fibrous nodule to enter the dermis of the skin and the connective tissue
⊛They also migrate to the eye and other organs of the body but rarely to the circulation.
⑥M.f from the skin and lymphatics are ingested, develop within the vector to become the infective larvae.
⑦In the stomach of black fly, M.f penetrate the gut wall, migrate to the thoracic muscles and moult twice over a week.
⑧The infective third stage larva then migrate to its mouth parts.
Infection is transmitted when an infected vector bites a person.
⊛The adult worm can live upto 15 years in human host
⊛M.f can live for about 1 year
What are the clinical features of Onchocerciasis？
The pathological lesions in the skin and eye result from a hyper sensitivity reaction to the dead or dying microfilaria.
1. Lesions:
The pathological lesions can be divided into two groups.
①Skin lesions
*Skin involvement typically consists of intense itching, swelling & inflammation.
*Acute pruritic rashes
*Lichenified onchodermatitis spotted depigmentation of the skin leads to “Leopard skin appearance, usually an anterior lower leg.
*Skin atrophy and loss of elasticity resulting in “Lizard skin “ appearance
⓶Onchocercoma (subcutaneous nodules)
⊛Are the typical lesions occurring on anatomical sites where the bones are superficial e.g. scalp, scapulae, ribs, knees
*They are visible or palpable & contains the adult worm.
*A granulomatous inflammatory reaction occur around the worms leading to granuloma formation, then fibrosis or calcification.
*They appear 3-4 month after the infection.
*The lesions are freely mobile, firm, smooth and rubbery in consistency
- Other manifestations
①Lymphadenopathy:
*M.f can cause inflammation of lymph nodes especially the inguinal & femoral areas. The enlarged lymph nodes along with loss of tissue elasticity can lead to a condition known as ‘Hanging groin - Ocular lesions and blindness
*It is particularly seen in persons with nodules on the head or face.
*Results from presence of M.f in the substantia propria of the cornea & anterior chamber leading to inflammation.
*Repeated inflammation in the cornea cause a chronickeratitis& sclerosis affecting the clarity of the cornea
*Clinical manifestation include conjunctivitis with photophobia, sclerosing keratitis, iridocyclitis, 2°glaucoma,optic atrophy & blindness - Secondary bacterial infection of the skin lesions
- Mazzoki reaction
*It is a symptom complex seen in patients after treatment with Diethylcarbamazine (DEC).
*Generally occurs within 7 days of treatment.
*Characterized by fever, urticaria, lymph node swelling, tachycardia, hypertension, arthralgias, oedema & abdominal pain. - Neurological disease such as epilepsy do occur esp in children
Diagnosis of Onchocerciasis?
①Microscopy
⊛M.f can be demonstrated by examination of skin snip placed in saline @ room temp during which M.f emerge
This method is specific & most accurate.
Adult worms can be detected in the
biopsies of subcutaneous nodule.
⓶Serology
⊛Useful in cases in which M.f are not demonstrated in the skin. Detects antibodies against specific onchocercal antigen.
⊛ELISA is more sensitive than skin snip tests
③Other Tests
⊛USG
Ultrasound is useful for detecting deep onchocercomas & vitreous changes in the eye.
⊛DEC patch test
Also known as Mazzoki patch test.
When the drug patch is placed on the skin, the infected persons show localized pruritus and urticaria as a reaction to dead M.f within 24 hours.
⊛Microfilariae may be directly observed during slit lamp examination of the eye.
Treatment of Onchocerca volvulus
①IVERMECTIN:
It is a drug of choice for Onchocerca infection.
Dose: single oral dose of 150 mg per kg weight
⓶HETRAZAN(DEC) and SURAMIN
DEC destroys M.f but usually causes an intense reaction (Mazzotti reaction)
③Doxycycline is macrofilariastatic & makes the female worm sterile as it targets the wolbachia endosymbiont spp of filarial parasites.
④Nodulectormy: Surgical removal of detectable nodules wherever possible
