Wuchereria Bancrofti

     Wuchereria Bancrofti are a species of parasitic nematode from the filarias family. Although there are three types of filarias that cause Lymphatic Filariasis, the Wuchereria bancrofti account for around ninety percent of all cases. The bancrofti effects over 100 million people in seventy-six countries within Africa, Central and South America, as well as tropical regions of Asia, Southern China, and the Pacific. The parasites tend to inhabit fresh, still bodies of water in tropical areas, or in swamps or marshes; similar to the mosquito which oftentimes ingests the bancrofti from infected humans, and then pass the larvae to other human hosts.

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   The agent starts its life as an egg as forty by twenty-five micrometers, and quickly grows to become 290 by six or seven micrometers in length as a microfilariae, or miniature version of its adult self. In its third stage of development, it is now an infectious larvae, and it is around this time where it develops its notable physical structures like the round mouth with surrounding papillae. After this stage, it is now considered a full adult. A typical adult will be translucent but cloudy with a long, skinny body. Often the tail ends of the nematode will coil or curl up. Females can be around thirty to a hundred millimeters in length while males are typically half the size.

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     The development of the nematodes varies in location. While the parasites are in a human host, they may lay eggs, which then develop into microfilariae, which migrate to blood and lymph vessels of humans. Because nematodes have no circular muscles, the parasites are forced to contract the longitudinal muscles down each of side of its body to move in a forward direction. When a mosquito penetrate the human host, the microfilariae are ingested. Once ingested, they will shed their sheaths, or protective, outer-layer and migrate to the midgut and thoracic muscles of the mosquitoes to develop further. They then use the mosquito as protection as they develop into infectious larvae and migrate to the head of the mosquito so that they are able to be “dropped off” on the next mosquito’s meal from a human host. After initial infection, it takes three to five months to develop into a full-fledged adult. The parasites live for around five years, but can even live up to ten years in some cases.

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The Three Species of Mosquitoes which can Host the Bancrofti

 

     Surprisingly, the Wuchereria bancrofti species requires two parasites of the opposite sex to reproduce. Structurally, the male worms have a corkscrew or coiled region on their tails which allow them to grasp female worms for reproduction. Also, the male genitalia, a “cloaca,” is surrounded with sensilla and spicules which are used to typically to help keep the female nematodes genitalia open for easy sperm transfer. The copulatory spicules act as reference, or guides for the male to physically open the female’s genitalia, while the sensilla, give the male a directional sense as to where it needs to approach, hence the prefix, “sens(e).” There has been evidence that, like many other mating species, the nematodes release chemical pheromones, or exhibit behavior to attract certain females to mate with. While in human hosts, the nematodes live together, coiled up as couples, male and female. Both male and female bancrofti are at sexual and reproductive maturity at around three to twelve months.

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     Lacking the ability to hear and see, the bancrofti relies solely on chemosensation to detect chemicals released by other parasites or by the human host. Also, the worms contain surrounding papillae around their mouths and bodies to help strengthen interactions with foods, other nematodes, and again the human environment. The worms use a diurnal rhythm, as well as their chemosensation to match the human lifestyle, by recognizing oxygen blood level to detect whether they are in a vein or arterial vessel compared to the typical lymph vessel. Impressively, this allows them to determine whether or not the human host is sleeping by analyzing blood oxygen levels, to indicate if they should rise to the surface of the peripheral circulation system to be eaten by mosquitoes for the further infection of another host.

While living in human hosts the parasites feed on bodily fluids and tissue. The bancrofti lodge themselves in lymph vessels which causes massive swelling, but their residency allows them to be surrounded by food at all times. Luckily for them, there are no known predators which can prey upon them while in the human host. Humans are in fact the only known natural host for the bancrofti, but there have been successful attempts to infect species of monkeys with the parasite. The bancrofti can live in four different hosts; one if which is a human, and the other three are all mosquito species.

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