LYMPHATIC FILARIAL WORMS Flashcards
What causes lymphatic filariaris?
*Wuchereria bancrofti
*Brugia malayi
*Brugia timori.
Over 90% of cases are caused by Wuchereria bancrofti.
Epidermiology of Lymphatic Filariaris
*Transmitted by mosquito vector species, which vary geographically.
*Considered endemic in 72 countries.
*Classified by WHO as the 2nd most common cause of long-term disability after mental illness.
WUCHERERIA BANCROFTI
*The disease involves lymphatics with clinical manifestations ranging from acute to chronic cases.
①Acute cases include: acute adenolymphangitis, filarial fever, tropical & pulmonary eosinophilia.
➁Chronic cases include: hydrocele, lymphedema & elephantiasis in the most severe of cases.
EPIDERMIOLOGY OF W. BANCROFTI
⊛The disease is endemic in over 72 countries.
⊛Endemic regions include South East Asia, Sub-Saharan Africa & some areas in Latin America.
⊛An estimated 70 million people in the world suffer from lymphatic filariasis.
⊛25 million people suffer from hydrocele and 15 million suffer from debilitating lymphedema.
W. BANCROFTI EPIDERMIOLOGY AND PREVALENCE IN ZAMBIA
⊛The prevalence in most sites is low although a few identified foci had prevalences above 25%.
⊛Highest prevalence (above 50%) was recorded from Kalabo district in Western Province.
⊛High prevalence foci located near national borders e.g. Luangwa, Serenje, Lundazi, Kalabo and Senanga.
⊛Anopheles. funestus & gambiae are the principal LF vectors
Habitat and Morphology of W. bancrofti：
Adult worms: lymphatic system
Microfilaria: blood
Morphology of Adult W. bancrofti worms:
*Translucent thread-like with smooth cuticle and tapering ends.
*Females are larger with a straight posterior end.
*Males are smaller with curved posterior with 2 spicules of unequal length.
*Female worm is viviparous -directly liberates sheathed microfilariae into lymph.
*The adult worms can live for 10–15 years or more.
W. bancrofti Microfilarial Morphology:
*The microfilaria has a colorless, translucent body with a blunt head and pointed tail.
*Covered by a hyaline sheath within which it can actively move forwards and backwards.
*Mf do not multiply or undergo any further devt in the human body.
*They die within 2–3 months If not taken up by a female vector mosquito.
Periodicity
*Mf circulate in peripheral blood in large numbers mainly at night (btwn 10 pm & 4 am).
*This correlates with the night biting habit of the vector mosquito & also the sleeping habits of the hosts.
LIFE CYCLE OF W. BANCROFTI:
W. bancrofti passes its life cycle in 2 hosts.
*Definitive host: Man.
*Intermediate host: Female mosquito of different species.
*Infective form: third stage filariform larva.
*Mode of transmission: bite of an infected mosquito carrying filariform larva.
Development in Mosquito(W. bancrofti)
①A mosquito vector takes in Mf as it feeds on a carrier during a blood meal and reach the stomach of the mosquito.
➁In the stomach, the Mf cast off their sheaths, penetrate the stomach wall & migrate to the thoracic muscles for further devt.
③It is actively motile and is the infective form.
④No multiplication of Mf in the mosquito hence 1 Mf develops into 1 infective larva only.
⑤Devt in the vector(extrinsic incubation period ) depending on environmental factors such as temp & humidity & also vector species.
⊛Under optimal conditions, its duration is 10–20 days.
⑥When a mosquito feeds on a person, the infective larvae get deposited on the skin near the puncture site.
Development in Man(W. bancrofti)
⑥The larvae enter through the puncture wound or penetrate the skin by themselves.
⊛To ensure transmission to man thousands of infective bites are needed per person.
⑦After penetrating the skin, larvae enter lymphatic vessels and are carried usually to abdominal or inguinal lymph nodes, where they develop into adult forms.
⊛There is no multiplication at this stage and only 1 adult develops from 1 larva, male or female.
⑧Sexual maturity occur in 6 months and mate.
⑨The gravid female worm releases large numbers of Mf as many as 50,000 per day.
①The Mf are ingested during a blood meal by mosquito & the cycle is repeated.
Prepatent period(W. bancrofti)
⊛Within 8-12 months ( biological incubation period)from entry of the infective larvae into the human host, Mf can be seen in circulation.
⊛Clinical incubation period is very variable, but is usually 8–16 months, though it may often be much longer.
PATHOGENESIS (W. bancrofti)
The manifestations are due to blockage of lymph vessels and lymph nodes by the adult worms. The blockage is due to:
①mechanical factors
➁Allergic inflammatory reaction to worm antigens and secretions.
⊛The lymph nodes & vessels are infiltrated by macrophages, eosinophils, lymphocytes & plasma cells.
⊛Vessel walls thicken and the lumen narrow or occludes leading to lymph stasis.
⊛Eventual dilatation of lymph vessels occur due to stasis which is further aggravated by damage to valves.
⊛Granuloma formation with scarring & even calcification occur.
⊛Increased permeability of lymph vessel walls lead to leakage of protein-rich lymph into the tissues.
⊛This produces the typical hard pitting oedema of filariasis.
⊛Fibroblasts invade the edematous tissues, laying down fibrous tissue, producing the non-pitting gross oedema of elephantiasis.
⊛Recurrent 2° bacterial infns cause further damage.
Acute clinic presentations include:
①Acute adenolymphangitis -characterized by repeated bouts of fever & painful lymphadenopathy.
➁Genitals are commonly involved in males resulting in painful epididymitis.
③Filarial fever - characterized by episodes of self-limiting fever without any associated lymphadenopathy.
④Tropical pulmonary eosinophilia - characterized by repeated bouts of dry nocturnal cough and wheeze.
Chronic clinical presentations include:
①Lymphedema
➁Hydrocele
③Lymphorrhagia
