Protozoa 3: Filiariasis Flashcards
Which ones are the filarial infections important for DTMH and why is treatment complex?
- Filariasis, Onchocerciasis, Loiasis are all parasitic nematode infections
- They are found across the tropical belt: notably Africa and Central/South America
- They are transmitted by insect vectors, which introduces larvae into human host that then develop into adult worms which produce microfilariae in the blood (or skin), that go on to reinfect the insect vector.
- They all cause chronic morbidity.
- Diagnosis is by identifying the microfilariae [MF] in the blood (or skin).
- The complexity of treatment lies in the fact that co-endemicity is common and treatment for one infection can cause serious adverse reactions in other infections. Public health programmes need to map infections before treating populations.
- The main method of control programmes is mass drug administration [MDA].
Which organism causes lymphatic filariasis and what is its life cycle?
- Wuchereria Bacnrofti
- Over 100 million people worldwide, endemic in over 80 countries
- Causes 90% of filiariasis worldwide
- Vector: any type of mosquito
- Male worms measure about 4cm and females 10cm
- Live mostly in lymphatics of the groin and scrotum
- Live for up to 10 years and females release up to 10000 microfilariae per day into peripheral blood which are alive for 1 - 2 years
Over 120 million people are infected, with about 40 million disfigured and incapacitated by the disease. Compare the distribution of lymphatic filariasis with the mass drug administration coverage to see how well we are doing at providing medication to those affected/at risk.
What are the clinical features of filariasis?
Clinical presentations include the following:
Majority are asymptomatic.
- Acute filarial fever without lymphadenitis
- Acute filarial lymphangitis
- This follows death of adult work, resulting in circumscribed inflammatory nodule, usually mild and rarely leads to residual lymphoedema
- Acute dermatolyphangitis
- Intense local inflammation with secondary bacterial infection in the presence of impaired lymphatic flow
- Chronic LF may develop months or years after acute symptoms:
- Lymphatic obstruction leads to lymphoedema
- Febrile lymphadenitis can occur and recur anytime post-infection
- Tropical pulmonary eosinophilia [TPE]: cough/wheeze, eosinophilia with lung infiltrates that goes on for weeks/months. There are rarely MF in peripheral blood so diagnosis is by filarial serology.
- Other manifestaitions:
- Acute epidydymitis
- Chyluria
- Funiculitis (sperm cord inflammation)
- Hydrocele (unilateral)
- Lymph scrotum
- Monoarthritis, glomerulonephritis
How do we diagnose filariasis?
- Now most common test: rapid finger-prick immunochromatographic card
- Most are not diagnosed but Rx empirically in areas covered by MDA programme.
- Microfilariae in blood (thick film) done by midnight sampling (peak of microfilarial periodicity between 2200 - 0200)
- Non-specific raised IgE, eosinophilia
Although people are not usually diagnosed but are treated as part of mass drug administration campaigns, diagnosis can be achieved by finding the microfilariae via microscopic examination of a Giemsa stained thick blood film. In most parts of the world, microfilariae only circulate in the blood at night so the timing of blood collection is important. There are also antibody tests available, but they are seldom used in the field.
How do we treat filariasis?
Treatments
• Microfilaria drugs:
o Diethylcarbamazine [DEC] + Albendazole stat annually (if giving DEC need to rule out loa loa first), or
o Ivermectin + Albendazole stat annually
o Doxycycline is effective at killing both microfilariae and adult worms
- For elephantitis/hydrocele/pulmonary eosinophilia Doxy for 6/52.
- Chyluria can require cystoscopic closure of the lymphatic-pelvic connection. Hydrocele usually requires surgical management as well.
Mass drug administration: albendazole (400 mg) together with ivermectin (150–200 µg/kg) or with diethylcarbamazine citrate (DEC) (6 mg/kg) given annually for 4–6 years to the entire at risk population, Surgery on hydrocoele, Skin care, Elevation of affected limbs, Treatment of adenolymphangitis, Exercise, Vector control
How does the WHO want to eliminate filariasis?
WHO response: Global Programme to Eliminate Lymphatic Filariasis (by 2020)
WHO’s strategy is based on 3 key components:
- Large scale MDA for 5 years in all regions where infection is present both treats infected people and interrupts transmission if adequate coverage. Choice of drug depends on co-endemic infections.
- Recommended basic care for chronic lymphatic filariasis
- Vector control
MDA: Albendazole plus either ivermectin or DEC as a single oral dose repeated annually for five years is now used for mass drug administration programmes.
Which organism is considered the eye-worm, what is its lifecycle, how is it transmitted and where prevalent??
Loa Loa
Localised to forest areas of west/central Africa (esp Cameroon)
• Transmitted via Chrysops deer fly
Larvae migrate subcutaneously, mature into 3-7cm long adult worms over course of a year -> survive for more than 15 years
Females produce microfilariae that are alive for 1 -2 years
What does the chrysops deer fly look like?
What are the clinical features of loa loa?
Symptoms are normally produced by adult worm
- Urticaria, pruritis, arthralgia, malaise
- Subconjunctival migration: intense pain and inflammation
- Can be removed from eye if local anaesthetic and surgical instruments present
- Trauma to migrating worm, however, may cause local inflammation -> CALABAR SWELLING
- Neurological complications only in patient with high microfilaraemia and following adminsitration of antihelminthics
- Hypereosinophilia common
How do we diagnose and treat loa loa?
Diagnosis
- Microfilaria in midday blood -> thick blood film using Giemsa/Wright stain
- PCR is best diagnostic method [serology non-specific for type of filaria]
- “Eye worms” are diagnostic
Treatment
- The benefits and risks of treatment have to be evaluated and are specialist
- Risk with high MF load of encephalitis with Ivermectin
- DEC can also cause encephalopathy if there is a high filarial load >8000mf/ml:
o <2500mf/ml then DEC divided into TDS regime for 21 days
o If >2500mf/ml then Albendazole for 21 days to reduce load followed by DEC
• Doxycycline not effective
Which organism causes onchocerciasis (river blindness), what is its life cycle, how is it transmitted and where prevalent?
- Caused by filarial worm Onchocerca volvulus
- Microfilariae transmitted by simulium black fly, typically in rivers/flowing water, that’s why it’s called river blindness
- Distribution 99% Africa, 1% in South America and Yemen
- recurrent exposure required to produce disease
- adult female threadlike, up to 40cm long
- live within human subcut tissue
What does the blackfly genus simulium look like?
What are the clinical features of onchocerciasis?
- Adults worms do not cause symptoms, most symptoms due to dying and dead microfilariae and endosymbiotic Wolbachia bacteria
- Symptoms of onchocerciasis are caused by an inflammatory reaction to the worms when they die in the sub-cutaneous tissue or the eye. Swollen limbs are associated with lymphatic filariasis (caused by other species of filarial worms). Onchocerciasis is not normally associated with vomiting
How do we diagnose onchocerciasis?
- Microfilariae in skin snips [punch biopsy is alternate technique] remains gold standard first line. Sensitivity can be low; new PCR/Elisa methods on skin snips. Microfilaria are in skin snips NOT in blood (since preference for subcut tissue)!
- Adult worms in biopsy specimens of skin nodules [excised or aspirated]
- DEC patch test –localised Mazzotti test
- Slit lamp exam may show microfilariae in anterior chamber of the eye
- Rapid serological antigen tests are now available but unhelpful in endemic areas
How do we treat onchocerciasis?
- Ivermectin 1-2x/year for >10 years: kills microfilariae not adults (live >10 yrs)
- Must map loa loa first “RAPLOA” to establish prevalence of co-endemic loa loa.
- Doxycycline is a new alternative/addition given daily for 6 weeks kills both microfilariae and a proportion of adult worms.
- Both drugs are contraindicated in pregnancy.
- DEC is contraindicated as it causes Mazotti reaction and accelerates blindness: This is characterised by an anaphylactic-type reaction.
Ivermectin is the recommended treatment for onchocerciasis. Treatment must be taken yearly for 10-15 years as the drug only acts on the microfilariae and does not kill the adult worms. In some countries, such as the USA, doxycycline may be used to treat the adult worms. Care must be taken when treating patients in Cameroon, the Central African Republic, the Congo, the Democratic Republic of the Congo, Nigeria and South Sudan as the Loa loa worm is endemic in these areas and treatment of Loa loa filariasis with ivermectin can cause severe allergic reactions.
Dermatological manifestations onchocerciasis
Loa loa eye worm
Calabar swellings are a transient subcutaneous swelling marking the migratory course through the tissues of adult Loa loa worms
Subcutaneous nodule in onchocerciasis
