Wuchereria bancrofti

Different species of the following genera of mosquitoes are vectors of W. bancrofti filariasis depending on geographical distribution. Among them are: Culex (C. annulirostris, C. bitaeniorhynchus, C. quinquefasciatus, and C. pipiens); Anopheles (A. arabinensis, A. bancroftii, A. farauti, A. funestus, A. gambiae, A. koliensis, A. melas, A. merus, A. punctulatus and A. wellcomei); Aedes (A. aegypti, A. aquasalis, A. bellator, A. cooki, A. darlingi, A. kochi, A. polynesiensis, A. pseudoscutellaris, A. rotumae, A. scapularis, and A. vigilax); Mansonia (M. pseudotitillans, M. uniformis); Coquillettidia (C. juxtamansonia). 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 . They develop in adults that commonly reside in the lymphatics . The female worms measure 80 to 100 mm in length and 0.24 to 0.30 mm in diameter, while the males measure about 40 mm by .1 mm. Adults produce microfilariae measuring 244 to 296 μm by 7.5 to 10 μm, which are sheathed and have nocturnal periodicity, except the South Pacific microfilariae which have the absence of marked 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 and can infect another human when the mosquito takes a blood meal .

Патогенез (что происходит?) во время Вухерериоза (слоновой болезни)

Источником вухерериоза является больной человек или паразитоноситель, источником бругиоза — человек и некоторые обезьяны. Непосредственными переносчиками инфекции являются комары.

Возбудитель вухерериоза Wuchereria bancrofti передается многими видами комаров, наиболее часто Culex fatigans, С. pipiens, Aedes polynesiensis. Развитие микрофилярий в комарах продолжается 8-35 дней в зависимости от температуры внешней среды. При укусе комара инвазионные формы микрофилярий попадают в кожу, активно внедряются в кровеносное русло и током крови заносятся в ткани. Превращение микрофилярий в половозрелые формы происходит спустя 3-18 месяцев после попадания их в организм человека.

В основе патогенеза вухерериоза лежат токсико-аллергические реакции, механическое воздействие гельминтов на лимфатическую систему и вторичная бактериальная инфекция. Как и многие другие гельминтозы, вухерериоз в некоторых случаях может не давать выраженной клинической картины. Иногда нет вообще никаких клинических проявлений инвазии. Бессимптомный вухерериоз имеют место в тех случаях, когда паразиты не закупоривают лимфатические сосуды и не вызывают воспалительных изменений в окружающих тканях. Больные с такими формами инфекции выявляются случайно при обнаружении у них микрофилярий в периферической крови.

Вухерерии в лимфатических сосудах, в том числе и в грудном протоке, сплетаются между собой в клубки, которые вызывают замедление лимфотока и лимфостаз. Паразиты вызывают воспалительное уплотнение стенок лимфатических сосудов, что, в конечном счете, ведет к закупорке сосудов в результате стеноза или тромбоза. Тромбированные лимфатические сосуды часто разрываются.

Из-за длительных лимфангитов и лимфаденитов в различных частях тела может развиться слоновость (элефантиаз).

Измененный эндотелий лимфатических сосудов, очаги некрозов в лимфатических узлах и окружающих тканях являются благоприятными местами для развития кокковой инфекции с образованием абсцессов. В результате жизнедеятельности паразитов и, особенно при распаде их образуются вещества, которые ведут к сенсибилизации организма с местными и общими аллергическими реакциями — эозинофилией, кожными высыпаниями и др.

Ciclo biol�gico de Wuchereria bancrofti:

Dependiendo de la distribuci�n geogr�fica, existen diferentes especies de mosquitos que sirven como vectores de la filariosis por W. bancrofti. Entre ellos est�n: Culex (C. annulirostris, C. bitaeniorhynchus, C. quinquefasciatus y C. pipiens); Anopheles (A. arabinensis, A. bancroftii, A. farauti, A. funestus, A. gambiae, A. koliensis, A. melas, A. merus, A. punctulatus y A. wellcomei); Aedes (A. aegypti, A. aquasalis, A. bellator, A. cooki, A. darlingi, A. kochi, A. polynesiensis, A. pseudoscutellaris, A. rotumae, A. scapularis y A. vigilax); Mansonia (M. pseudotitillans, M. uniformis); Coquillettidia (C. juxtamansonia). Durante la ingesti�n de sangre, el mosquito infectado introduce las larvas filarias de tercer estadio dentro de la piel del hospedador humano, donde penetran en la herida a trav�s de la mordedura . Se desarrollan en adultos los cuales residen com�nmente en los linf�ticos . Las hembras miden de 80 a 100 mm de largo y de 0.24 a 0.30 mm de di�metro, mientras los machos miden cerca de 40 mm por 0.1 mm. Los adultos producen las microfilarias que miden de 244 a 296 μm por 7.5 a 10 μm, que presentan vaina y tienen periodicidad nocturna, con excepci�n de las microfilarias del Pac�fico sur que presentan ausencia de periodicidad marcada. Las microfilarias migran dentro de los canales de la linfa y sangre movi�ndose activamente a trav�s de la linfa y la sangre . El mosquito ingiere a las microfilarias durante la ingesti�n de sangre . Despu�s de la ingesti�n, las microfilarias pierden sus vainas y algunas penetran a trav�s de una porci�n de pared del proventr�culo y del cardias del est�mago del mosquito alcanzando los m�sculos tor�xicos . Es ah� donde las microfilarias se desarrollan en larvas de primer estadio y posteriormente en larvas infectantes de tercer estadio . Las larvas infectantes de tercer estadio migran a trav�s del hemocele hacia la prob�scide del mosquito infectan a otro humano cuando el artr�podo se alimenta de sangre .

Wuchereria Bancrofti are filarial worms are long, thin tapering worms without lips around mouth. The oesophagus does not possess a bulb. The life cycle involves a blood sucking insect. Adults are filarial worms and they produce microfilariae.

This is also called as Filaria bancrofti. It lives in man in warm countries such as Arabia, India, Malaya, China, Korea, Japan, West Indies, Brazil and South Pacific Islands. In India, it mainly occurs along sea coast and along the banks of large rivers except Indus. It causes elephantiasis or wuchereriasis or Bancrofti’s filariasis. The filarial worm is a dreaded human parasite.

Morphology of Wuchereria Bancrofti:

The adult worm lives coiled up in the lymph glands and lymph passages of man. Adult female averages 82 mm long and 0.25 mm wide,. The male is smaller, average 40 mm in length by 0.1 mm in width. The head end is slightly enlarged. The mouth is a simple hole without lips. The mouth leads directly into oesophagus with a buccal cavity.

The oesophagus does not possess the bulges and constrictions. The vulva opens to the outside of the body in the midregion of the oesophagus. The male possesses two spicules of unequal length and a gubernaculum.

Microfilariae:

The females are ovo-viviparous, lay eggs with well developed embryos. The embryos are known as microfilariae having a length 275 um. They pass through lymph nodes and reach the main lymphatic trunks into the circulating blood.

Microfilaria stops further development in human beings. If they are not sucked by the mosquito (intermediate host) they die. The life span of microfilaria is about 70 days.

Microfilaria occurs as two biologically different forms. Larvae of oriental countries like India and China, show marked nocturnal periodicity i.e. they appear in peripheral blood during night (between 10 p.m. to 4 p.m.) They are transmitted by night-biting mosquitoes, Culex fatigans. Larvae of Pacific Islands like Polynesia show diurnal periodicity and they are transmitted by day-biting mosquitoes, Aedes polynesiensis.

In the larvae of oriental countries, microfilarial periodicity depend on alternate:

1. accumulation of the microfilariae in the lung capillaries, usually by day (active phase) and

2. approximately even distribution throughout all the circulating blood usually by night (negative phase).

Wuchereria bancrofti is a digenetic endoparasite, and complete life cycle in man, the definite host and mosquito (Culex & Aedes), intermediate host.

Stages in Mosquito:

Microfilaria is sucked from peripheral blood of man. The sheath of microfilaria digests in the stomach of mosquito. Then larvae penetrate stomach wall and reach thoracic and wing muscles. In next couple of days slender microfilaria changes to a thick, short sausage form with a short spiky tail. It has a rudimentary alimentary tract and is the first stage larva.

In 3 to 7 days, it grows and moults twice giving rise to second stage larva. Development proceeds forming body cavity, digestive system, genital organs etc. It is the third stage larva. It measures 1500 to 2000 um in length and migrate into the mosquito’s labium as infective stages.

When mosquito bites a fresh human host, infective juveniles comes out the labium on the skin of the victim. Filariform larvae penetrate through the wounds made by the mosquito. Worm larvae travel from the point of entry into human skin to the lymphatics. They grow and moult twice before becoming adults.

Pathogenesis of Wuchereria Bancrofti:

The pathogenic effect of Wuchereria bancrofti are produced by the adult either living or dead. Light infection produces no serious symptoms. It causes filarial fever, head ache and mental depression. In heavy infection, the adult, living or dead blocks lymphatic vessels and glands, resulting in various pathological conditions.

When the disease has caused the enlargement of such organs as the scrotum, breasts or legs, it is called elephantiasis. The adult worm causes an inflammatory reaction of lymphatic system or lymphangitis, obstruction of lymph in the organs results in their enlargement called lymphedema. The enlargement of lymphatic glands also lead to lymphadentis. Adult and microfilariae produce lesions in lymph node and also granulomas in spleen.

Occasionally hyperplasia of muscle fibres may be observed. Symptoms of filarial infection include fever, tenderness of infected parts, eosinophilia inflammation and transient swelling. Anxiety caused by fear is of considerable importance. Thick blood smears are preferable in examinations for microfilariae.

Treatment of Disease Caused by Wuchereria Bancrofti:

No proper medicine is available to eradicate the filaria worms.

However, following filarial drugs can be used:

1. Mel, W. It is an arsenical preparation effective on adult worms.

2. Heterazan compound (Diethyl carbamaide) can be used to check microfilariae.

3. MSb (Paramelaminyl phenyl stibonate) is effective on infective larvae and immature adult worm.

Control of Disease Caused by Wuchereria Bancrofti:

1. Eradication of mosquito by insecticide or by other control measures.

2. Reducing infection amongst mosquitoes.

3. Treatment of carriers by using heterozon and cyanine.

4. Movement from areas of infection.

5. Protection from mosquitoes, using mosquito net or mosquito repellent while sleeping in night, and

Asia (China, India, Pakistán, Indonesia, Japón, Malasia, Birmania, Filipinas y Sri Lanka), África (países tropicales y Egipto), América (Central y del Sur y Caribe) Oceanía. R. Humano. MT. Picadura de mosquitos (Culex spp, Aedes spp, Anopheles spp, Mansonia spp y Coquillettidia spp).

No se transmite de persona a persona.

Período de incubación: 5-18 meses (las microfilarias aparecen en sangre periférica a partir de los 8 meses del contagio).

Infección.

Wuchereriasis. La mayoría de pacientes infectados permanecen asintomáticos. Manifestaciones agudas: linfangitis aguda, funiculitis, orquiepididimitis, eosinofilia pulmonar tropical.

Manifestaciones crónicas: filariasis linfática (linfedema, hidrocele crónico, ulceración e infecciones secundarias, afección renal con quiluria, hematuria, proteinuria y eventual déficit nutricional incluyendo anemia e hiponatremia). Eosinofilia pulmonar tropical.

Diagnóstico.

• Examen de sangre en fresco o en muestras concentradas o filtradas. Las microfilarias pueden observarse en el sedimento de orina centrifugada. Tinciones de Giemsa o hematoxilina-eosina para el diagnóstico de especie. Es conveniente realizar la extracción sanguínea por la noche, cuando el número de filarias circulantes es mayor.
• Serología.
• Técnicas de Biología Molecular (PCR).
• Ecografía para detectar la presencia de gusanos adultos.

Tratamiento

Dietilcarbamacina 1.er día 50 mg, 2.o día, 50 mg/8 h, 3.er día, 100 mg/8 h, y días 4 a 14, 6 mg/kg/día. Otra opción es 6 mg/kg en dosis única. No se debe utilizar en áreas de oncocercosis por el riesgo de ceguera

Corticoides y/o antihistamínicos. En todos los casos puede asociarse doxiciclina (activa frente a Wolbachia, bacteria intracelular simbiótica con las filarias) 100-200 mg/día oral, 6-8 semanas (existe poca experiencia).

Alternativas: Ivermectina (microfilaricida) 200 μg/kg en dosis única con o sin albendazol (macrofilaricida) 400 mg oral en dosis única. Es conveniente comenzar el tratamiento al cabo de 2-3 días del brote agudo de linfangitis. Puede ser necesario repetir el tratamiento al cabo de 6 meses.