Filariasis Flashcards
What species cause lymphatic filariais?
Which species is most common?
- Wuchereria bancrofti (>90% of infec- tions worldwide)
- Brugia malayi (Asia)
- Brugia timori (Asia)
What is the global distribution of Lymphatic filariasis?
- > 60% of cases in Southeast Asia
- ~30% in sub-saharan Africa
Distribution of LF
What strategy is used for elimination of lymphatic filariasis
- Mass distribution of antifilarial drugs
- DEC or ivermectin monotherapy
- DEC or ivermectin in combination with Albendazole
What is the vector for lymphatic filariasis
Mosquitoes
* Culex
* Anopheles
* Aedes
* Mansonia
* Ochlerotatus
* Culex quinquefasciatusis the primary vector in towns
How do mosquitoes transmit LF pathogens to humans?
- Filariform larvae migrate to the mouthparts of the mosquito after 10 days or more
- In contrast to malaria filariform larvae are not injected directly into the bloodstream but are deposited on the skin of the new human host during feeding
- Filariform larvae then actively invade the new host via the biting area
- *There is no multiplication of larvae in the mosquito.
Describe the life cyle of Wuchereria bancrofti
- During a blood meal, an infected mosquito introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound image .
- They develop in adults that commonly reside in the lymphatics image .
- The female worms measure 90 mm x 25 mm in diameter, while the males measure about 40 mm x 1 mm. Adults produce microfilariae measuring 280x8 μm, which are sheathed and have nocturnal periodicity. The microfilariae migrate into lymph and blood channels moving actively through lymph and blood.
- A mosquito ingests the microfilariae during a blood meal.
- After ingestion, the microfilariae lose their sheaths and some of them work their way through the wall of the proventriculus and cardiac portion of the mosquito’s midgut and reach the thoracic muscles.
- There the microfilariae develop into first-stage larvae
- and subsequently into third-stage infective larvae .
- The third-stage infective larvae migrate through the hemocoel to the mosquito’s prosbocis image and can infect another human when the mosquito takes a blood meal
What are the diagnostic methods for lymphatic filariasis
*Giemsa staining of thick blood films taken at peak microfilarial periodicity (22-0200 for W. bancrofti)
* Scrotal ultrasound for filarial dance
* ELISA
* Finger-prick immunochromatographic (ICT) card
* ICT highly sensitive and specific and preferred method for diagnosis
What are the treatment options for lymphatic filariasis
- Diethylcarbamazine (DEC) 10-14 days
- Ivermectin used in combination with DEC or albendazole
- Albendazole 400mg single dose
- Doxycycline 4-6 weeks
What are the important considerations for drug choice in treating lymphatic filariasis
- Co-infection with onchocerciasis = do not give DEC - Mazotti reacion
- Co-infection with loa loa = do not give DEC (encephalopathy) or ivermectin
- If co-infectino with loa loa, microfilaremia must be reduced with albendazole prior to treatment with DEC or ivermectin
Do the common treatments for LF affect microfilaria, adult worms, or both?
- DEC - affects microfilaria. Limited effects on adult worms
- Ivermectin - kills microfilaria but not adult worms
- Albendazole - kills microfilaria and can effect adult worms as a longer course
- Doxycycline - micro and macrofilaricidal
What causes tropical pulmonary eosinophilia?
- Lymphatic filariasis
- A syndrome of wheezing, fever and eosiniphilia seen predominantly in the Indian subcontinent and other tropical areas
- Due to an exaggerated immune response to the filarial antigens which includes type I, type III and type IV reactions with eosinophils
- Eosinophilia is strikingly high (>3000/μl)
What are some of the advantages of using doxycycline in treating lymphatic filariasis? Disadvantages
Advantages
* Eliminates microfilariae gradually, thus avoiding adverse inflammatory events that may follow rapid destruction of parasites and release of bacterial symbionts
* Adults are also gradually eliminated avoiding the development of inflammatory nodules sometimes seen with rapid death of adult worms following treatment with DEC or ivermectin.
* Eliminates Wolbachia surface protein, the inflammatory trigger for chronic disease
Disadvantages
* Longer course and therefore can’t be used in mass drug administration programs
What are the 2 key components of the Global Programme to Eliminate Lymphatic Filariasis
- Mass drug administration (MDA)
* Annual large-scale administration of a single dose of albendazole (400mg) with either ivermectin (150–200 μg/kg) in areas where onchocerciasis is also coendemic, or with DEC (6 mg/ kg) in areas where onchocerciasis is not en- demic.
* MDA must be continued for 4–6 years to fully interrupt transmission. - Morbidity management and disability prevention
Clinical severity of lymphoedema and acute inflammatory episodes can be reduced by simple measures of
* hygiene
* skin care
* exercise
* elevation of affected limbs
When is vector control a recommended strategy for LF
- some areas that are coendemic for L. loa;
- Countries where the disease burden is heaviest (e.g. Bangladesh, India, Indonesia, DRC and Nigeria) and which need to rapidly scale up MDA;
- Pacific Island countries, where interruption of local transmission has been achieved but there is
limited experience in preventing recurrence.
True or false: In tropical pulmonary eosinophilia microfilariae will be seen on blood films
False
Microfiliariae are trapped in the pulmonary vasculature and will not be seen on blood smear.
Antibody test will be positive.
Think asthma like presentation that doesn’t improve with bronchodilators in patient from endemic area
