Wuchereria bancrofti: An Elephant of a Problem

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Introduction:

Wuchereria bancrofti is a thread-like nematode that is one of the three different nematodes that cause Lymphatic filariasis in humans. Today, there are 120 million people infected with these parasites. These parasites can be found in 80 countries: in the humid and tropical areas (where mosquitos are apparent) of Africa, Asia, isolate America areas, and the Pacific islands. Usually in areas of poverty. The symptoms of this parasite are usually asymptomatic. This parasite will not cause harmful symptoms until the body reacts and the lymphatic tissues (usually in the groin and the legs) begin to swell. Often, the infected that are left untreated will develop elephantiasis in the legs and groin region. This parasite itself is not deadly, but left untreated can cause deadly infections and can ultimately hinder a person mobility[1].

Symbiont Description:

The Wuchereria bancrofti are thread-like nematodes. The female nematodes are normally 10 cm long and .2mm wide while the males are 4 cm long. These organisms thrive in the hosts lymphatic system and can produce around 50,000 microfilaria a day [2]. These microfilaria leave the lymphatic system and circulate the body. During the day, they thrive in the lungs and at night, they sense their hosts body temperature drop, and travel and emerge in the peripheral veins/arteries at night in order to spread through a vector, typically a mosquito [3]. Wuchereria bancrofti can live as in the body as microfilaria for up to 12 months. It takes about 6-12 months for Adult worms to develop from the larval stage and can live up to 4-6 years [2].

Female W. bancrofti [6] Male W. bancrofti [6]

Host Description:

These nematodes usually begin transmission through a mosquito vector and transmission is completed when the mosquito bites a human. Typically, mosquitos bite during the night in humid areas. Humans are the only known host. [3]

Life Cycle:

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As previously stated, the Wuchereria bancrofti has two hosts: a mosquito and a human. The CDC has listed the mosquito as being the first step of this nematodes lifecycle. The first part of their lifecycle occurs when an infected mosquito bites an innocent standby for a lovely meal. The third stage larvae will enter into the human through the opened bite made by the mosquito. It is then that these larvae make their way to the lymphatic tissues where they will develop into adults [4]. This can take up to 12 months [1]. The adults will then mate and create up to 50,000 microfilariae a day [1]. As a 'new born' the microfilariae are sheathed. As stated previously, during the day, the microfilariae are found in the lungs and during the night, they sense a change in their hosts' body temperature and will migrate to the peripheral veins/arteries where they await to be found by a hungry mosquito [4]. They follow the hosts sleep cycle as they migrate to the peripheral veins/arteries [8]. The mosquito will unknowingly consume the microfilariae during their meal. Once inside the mosquito, the microfilariae will then loose their sheaths where they will find their way to the mosquitos midgut and their thoracic muscles. In 1-2 weeks, they will turn into first stage larvae and then gradually develop into a third-stage infection larvae where they are then able to infect another host, thus the life cycle restarts [4].

Ecology:

This parasite only has two hosts: human and mosquito (vector). It is prevalent in humid climates and where mosquitos actively are. As mentioned before, these areas are the humid and tropical areas (where mosquitos are apparent) of Africa, Asia, isolated areas in the Americas, and the Pacific islands [1]. The bottom map shows these particular areas that are affected with this parasite.

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Today, 120 million people today are affected by this parasite. Even more devastating, more than 30% of this infected populace are severely incapacitated by the horrendous disease this parasite causes. In the 80 countries this parasite is associated with, 1 billion people are at risk for being infected [1]. This disease is diagnosed with a simple test. An antigen-detection test, known better as the ITC test can scan blood sample and will reveal the results within minutes. The treatment of these parasites and the disease that it causes is three anti-parasitic drugs, albendazole and mectizan, and the possible surgical removal of the swollen limbs. Even then, the people affected with this disease aren't able to get back their mobility. The Global Alliance to Eliminate Lymphatic Filariasis is an active partner to the World Health Organization (WHO) whom are actively trying to rid the world of this disease. Several feats that they are implementing is having mass drug administration of this parasites killer Albendazole, Mectizan, and DEC. The latter drug has one set back: It cannot be used in African countries. When using this drug, severe side reactions can occur when other infections of the body, such as river blindness, are present. Instead the first two drugs are more commonly used [7]. Both American drug companies, Glaxo Smith Kline and Merck, are committed to fund free medication for this eradication program [8]. Other ways this group is fighting this parasite is through passing out mosquito bug nets, to prevent mosquito attacks [7]. Below is a video of this movement.

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The Wuchereria bancrofti is a perfect example of circadian periodicity and emerging when their 2nd host, the mosquito, feeds [5]. The microfilariae senses a change in their hosts body temperature and will make way to their hosts peripheral blood vessels and remain there until they sense another change in body temperature and will then return back to the lungs [1]. As mentioned before, the microfilariae move in rhythm with their hosts sleep cycle [8]. While in the peripheral blood vessels, the microfilariae hope to get picked up by the 2nd host, the mosquito, where they will then grow and develop into their infectious larval stage and will hopefully reach another human host [1].

Below is a video describing this parasites life cycle.

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Sources:

1. http://www.parasitesinhumans.org/wuchereria-bancrofti-lymphatic-filariasis.html

2.http://www.phac-aspc.gc.ca/lab-bio/res/psds-ftss/wuchereria-bancrofti-eng.php

3. http://animal.discovery.com/invertebrates/monsters-inside-me/lymphatic-filariasis-w-bancrofti/

4. http://www.dpd.cdc.gov/dpdx/html/frames/a-f/filariasis/body_Filariasis_w_bancrofti.htm

5. http://emedicine.medscape.com/article/996732-overview

6.http://www.science.smith.edu/departments/Biology/SWILLIAM/fgn/pnb/wuchban.html#path>pathologies described below.

7. http://www.filariasis.org

8. http://www.youtube.com/watch?v=dnWwHthkGkY&feature=player_embedded

9.http://animal.discovery.com/videos/monsters-inside-me-the-filariasis-parasite.html