Filariasis Flashcards
What are some filarial infections?
Lymphatic filariasis
- Caused by parasite Wuchereria bancrofti - typical of this is a sheath around larva
- Brugia timori/Brugia malayi
Loaiasis (eye worm)
- Caused by loa loa
Onchocerciasis (blinding worm)
- Onchocerca volvulus – causes river blindness
Others
- Mansonelliasis
- Mansonella perstans/M. streptocerca/M. Ozzardi
Life cycle
Transmitted by mosquito vector
Bites and in saliva the L3 Larvae are transmitted into the skin
Larvae will migrate and develop into adults, live in lymphatics
Populate and the female produces sheath like filaria into circulation, found in lymphatics and blood
Mosquito takes up the filaria in the blood and undergoes further development
What are parasites?
White, slender, roundworms
Three types: Wuchereria bancrofti, Brugia malayi, Brugio timori
Live for 5-7 years in lymphatics, female adult produce millions of offspring
Adults block the lymphatic system
- Network of channels and lymph nodes that help maintain fluid levels in the body
- Blockage leads to edema (collection of fluid in tissues)
Epidemiology of lymphatic filariasis
Human lymphatic filariasis is caused mainly by Wuchereria bancrofti, but also brugia malayi and brugia timori
Estimated 90-120 million people infected in 72 countries, >90% have bancroftian and <10% have brugian filariasis
Vectors
- Culex in urban and semi-urban areas
- Anopheles in rural areas of Africa and elsewhere
- Aedes in islands of pacific
Clinical disease
- 25 million men have genital disease, most commonly hydrocoele
- 15 million mostly women have lymphoedema or elephantiasis of the leg
- LF accounts for 2.8 million DALYs
South american continent, mainly brazil
Guyanas as well
Equatorial africa
Southeast asia
Clinical presentation of filiariasis
Adults live in lymphatics
- Dysfunction of lymphatics
- Filarial fever when adults die in lymphatics
- Recurrent
- Fever
- Acute lymphangitis
Acute dermatolyphangioadenitis – inflammation of lymph node, lymphatics and overlying skin
Lymphoedema
Chronic damage to lymphatic leads to progressive lymphoedema
men get scrotal hydrocele, fluid accumulates in membrane surrounding scotum
tropical pulmonary eosinophilia
What is acute filarial lymphangitis (filarial fever)?
Adult worms have died in lymphatics causing acute inflammatory response.
cumulative damage to lymphatics causes accumulation of fluid (particularly in lower limbs) causes lymphoedema.
acute dermatolymphangioadenitis related to secondary bacterial infection that defers damage to lymphatics.
How does hydrocele occur?
Results from accumulation of fluid
Get damage to lymphatics around it that drain scrotum
Accumulation of fluid around scrotum, scrotum enlarges, over time get elephantiasis
Elephantiasis of breast, key to prevent further progression of elephantiasis and secondary infections is cleaning the swollen legs twice a day with soap and water
Major impact in rural communities for agriculture productivity
Tropical pulmonary eosinophilia
W.bancrofti microfilariae (mf) sequestered in lungs during the day
During day microfilariae stay in lungs, at night they go into blood
In the lungs they can cause an allergic type response.
Hypersensitivity reaction to mf in pulmonary blood vessels <1% of patients
- Absent mf on blood films because you have strong immune response to mf
- So you have to do blood sampling at night because that’s when you find mf in blood, but you may not find them because there are v few mf with a strong immune response
Typically men in 20-40s
Presents as chronic, non-productive cough which is more severe at night, wheezing, fever
Weight loss, malaise, adenopathy
On chest x-ray you see diffuse nodular infiltrate
Eosinophilia, elevated IgE and anti-filarial antibodies
Untreated may progress to interstitial fibrosis of lungs
Social impact of the disease
Sexual disability
Communities frequently shun those disfigured
Inability to work
Women with visible signs may never marry or spouses and families will reject them
Diagnosis
Thick smears using capillary blood at night for W.bancrofti 10pm to 2am
Knotts technique using 1mL blood
Rapid tests to detect circulating antigen
Anti-filarial IgG antibodies
PCR to detect parasite DNA in blood
Ultrasound – filarial dance sign
Management of filariasis
Treating the infection: DEC (6mg/kg per day) for 12 days in bancroftian filariasis and for 6 days in brugian filariasis, repeated at 1-6 monthly intervals if necessary
Ivermectin
Albendazole
Side effects: headaches, fever, myalgia, lymphadenopathy and occasionally rash, itching
Managing LF, lymphoedema and hydrocele
Acute dermatolymphangioadenitis managed with antibiotics, antipyretics, analgesics
Lymphoedema and elephantiasis managed with hygiene, antibacterial creams, antifungal creams
Hydrocoele managed with surgery
treatment and management of elephantiasis
Prevention
- Mosquito nets, insect repellents
Voodoo healing techniques
Elevate and exercise affected body part
Skin treatment
- Wash area twice daily
- Antibacterial cream
CDP (complex decongestive physiotherapy)
- Lymph drainage, massage, compressive bandages
What is the current reigmen to eliminate LF transmission?
Once yearly single dose two or three drug regimen as community-based MDA
Ivermectin + DEC + albendazole
Where onchocerciasis is co-endemic, ivermectin+albendazole
Where loiasis is co-endemic, albendazole alone
What is onchoceriasis/ river blindness?
Geographic distribution?
Major blinding disease
Caused by filarial parasite Onchocerca volvulus
Transmitted by blackflies
Formerly in parts of latin america, in most of these areas it is now eliminated
Still endemic in venezuela and brazil and countries in africa
Transmission of onchoceriasis?
Infection transmitted by simulium black flies, transmit microfilaria
Microfilaria will develop either into males or females
Females live under skin in fibrous nodules, males migrate from nodule to nodule, fertilising females.
Females release thousands of microfilaria which are found in the skin
In a blood meal the blackfly will take up microfilaria to keep up the life cycle.
Pathology of onchoceriasis?
Repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring in skin and eyes
Adults within subcutaneous nodules do not cause pathology except where they interfere with movement e.g at joints
Cllinical disease onchoceriasis
Onchocercal nodules under skin
Skin disease
- Acute papular onchodermatitis
- Chronic onchodermatitis
- Sowda
Eye disease
Anterior segment
- Punctuate keratitis
- Acute iridocyclitis
- Sclerosing keratitis
Posterior segment
- Optic neuritis/atrophy
- Chorioretinopathy
Subcutaneous nodules, acute papular onchodermatitis, sowda, chronic onchodermatitis, hanging groin in onchocerciasis
On the head, females release microfilaria which can invade the eyes
If you cut open nodules you see females
Acute papular onchodermatitis
- Allergic inflammatory response caused by microfilaria in skin
- Papules represent where microfilaria has been recognised by immune response
Sowda
- Extreme hypersensitivity to presence of microfilaria
- Blackening of skin
- Localised sowda
Chronic onchodermatitis
- Chronic damage to skin and elastin collagen in the skin causes premature aging of skin
- Particularly around thighs and buttocks where most nodules are found
- Hyperkeratosis to skin due to secondary infections
Hanging groin - Loss of elasticity to skin, causes large inguinal lymph nodes hanging over groin
What are eyes examined for in onchoceriasis?
Front of eye you get punctuate keratitis, where microfilaria invade corneal stroma and you get inflammatory response around it - resolves without scarring
Inflammation of iris, iris sticks to lens – iritis
Blockage of fluid from anterior chamber resulting in glaucoma
With repeated episodes of inflammation you get vascularisation of cornea, sclerosing keratitis – causes blindness
What is chorioretinopathy and optic atrophy
Back of eye, normally optic nerve is seen
With onchocerciasis you see mothling lateral to pigment epithelium
Pigment epithelium and retina overlying dies, overtime becomes extensive, get pigment clumping and you see sclera underneath
Damage to nerve cells and secondary damage to optic disc
Optic atrophy from microfilaria alone, causing inflammation resulting in damage to optic disc
How do you diagnose onchoceriasis?
Using a punch of skin from around the hips, put it on slide with saline and look under microscope
Can see microfilaria
Also take nodules and cut them open to see adult worms inside
Antibody test to pick up exposure to infection
Treatment of onchoceriasis
Macrofilaricidal drugs – kill adults
- Suramin – anti cancer drug, severe side effects
- Amocarzine – severe side effects
- Tetracycline – daily for 6 weeks but effective
Microfilaricidal drugs – more widely used - - Diethylcarbamazine – adverse effects e.g papular dermatitis
- Ivermectin – less effects
Control strategies for onchoceriasis
Nodulectomy
- Systemic campaigns of nodulectomy reduced microfilarial burdens in Ecuador and Mexico
Vector control
- Extremely effective in volta River basin but suspended in 90s because complex to administer and expensive
Ivermectin
- Introduced in early 90s
- Now mainstay of control
- Treatment annual or semi-annual
Others
- Tetracycline, moxidectin, flubendazole
What is loaisis?
Eye worm infection transmitted by chrysops fly which causes a painful bite
Transmit L3 larvae, which develop into adults, migrate through tissues under the skin
Female produces thousands of larvae found in peripheral blood
Chrysops fly takes up microfilaria from blood and continue life cycle
Epidemiology of loaisis
Loa loa found in west and central africa
Transmitted by bites of deerflies (genus Chrysops), most common during rainy season and found in high-canopied forest
Human and baboon natural hosts
People most at risk for loiasis are those who live in certain rain forests in west and central africa
Estimated 3-13 millions infected
Adult females 5-7cm, males 3cm long
Clinical presentation of loasis
Asymptomatic
- Adult worms migrate through subcutaneous tissues at 1cm/min and can survive up to 17 years
- However increased mortality in heavily infected
Eye worm
- Takes a few hours to a weak to cross sclera
- Accompanied by conjunctivitis and swelling
- Sometimes worm can get lost
Recurrent calabar swellings
- In tissues where worms die it causes inflammatory reactions, calabar swellings
- Extremities and face, generally painless
- Painful near joints
Rare
- Invasion of brain by microfilaria causing meningoencephalitis
- Renal-immune complex mediated or mechanical trauma from mf
- Endomyocardial fibrosis
Calabar swellings
- Episodic angioedema
- Most commonly affects extremities
- Lasts 1-4 days
Diagnosis of loasis
Definitive diagnosis
- Detection of microfilaria in daytime blood
- Identification of adult worm in the subconjunctiva or subcutaneous tissue
- PCR using loaf loa repeat sequence
Presumptive diagnosis
- Compatible clinical picture and positive antifilarial antibodies
- Problematic due to geographical, serologic and clinical overlap with other filarial infections
Treatment of loasis
DEC (diethylcarbamazine) treatment of choice for those with no or few circulating mf
- DEC 8-10 mg/kg/day for 21 days
- May be severe side effects among those with high levels circulating microfilariae
Albendazole useful in DEC- refractory cases or to reduce mf counts
Ivermectin
- May be severe, life-threatening side effects among those with high levels circulating microfilariae (ie >3000 mf/ml)
Prophylaxis
- Weekly DEC in travellers to endemic areas
- Avoid chrysops bites
Control of loasis
No control programmes but many areas are co-endemic with onchocerciasis and/or LF where control programmes are in operation
- Co-endemic regions with onchocerciasis prelude use of ivermectin in MDA for loa loa
- Recommendation for twice annual albendazole in co-endemic regions but epidemiology inadequate
