NIH-Funded Scientists Solve Genetic Code of Parasitic Worm that Causes Elephantiasis

Introduction

Statistics shows that approximately 150 million people worldwide are infected with filarial parasites which are long, thread-like worms. They have the capacity to thrive for years inside the human body and cause serious, debilitating diseases such as elephantiasis. Tissue samples of elephantiasis can be closely scrutinized with the use of the tissue culture microscope. The culprit responsible for elephantiasis are mosquitoes which spread the larvae of the parasitic nematodes from human to human, thus placing at risk more than a billion people who live in places in Africa, Asia and Latin America where filarial parasites abound. What is elephantiasis?

Elephantiasis is a disease which is characterized by the thickening of the skin as well as the underlying tissues, especially in the legs and genitals. Tissue samples of elephantiasis can be viewed well in the tissue culture microscope. It is due to the obstruction of the lymphatic vessels caused by a parasitic disease commonly referred to as lymphatic filariasis. Elephantiasis may likewise occur in the absence of parasitic infection as noted under the tissue culture microscope. The nonparasitic form is commonly known as nonfilarial elephantias. It is also called podoconiosis and occurs in the mountains of Africa. It is believed that nonfilarial elephantiasis may be due to frequent contact with the volcanic ash. What are the genetic uses of these parasites?

A team of researchers from the National Institute of Allergy and Infectious Diseases has successfully revealed the genetic secrets of these parasites as published in the Science. In their report they have solved the complete genome of Brugia malayi. Brugia malayi is one of the worms known to cause debilitating disease elephantiasis. Based on the World Health Organization estimates, there are approximately 40 million people worldwide who are gravely incapacitated and disfigured by elephantiasis. The WHO likewise approximates that about half a million people around the world have lost their vision due to onchocerciasis, or river blindness, which is caused by still another type of filarial parasite.

Although filarial diseases are treatable, the current treatments were discovered decades ago. There is an urgent need for novel discoveries in this area because of the limitations of the current drugs, including toxicities and the development of resistance.

The B. malayi genome shows dozens of possible new targets for drugs or vaccines and should provide new opportunities for understanding, treating and preventing elephantiasis as well as similar diseases.

A complete genetic blueprint allows for a better understanding of what genes are important for different processes. This way they can be targeted more specifically according to Elodie Ghedin, Ph.D., who led the sequencing project

How is Elephantiasis Spread?

Mosquitoes are the known culprit in the transmission of the disease. When a mosquito bites someone infected with B. malayi, it ingests microscopic worms that develop into infectious larvae. Once deposited onto the skin, the parasite penetrates it and then finds the way to the body’s lymphatic system.

The lymphatic system is network of fine vessels and organs responsible for draining fluid from the body’s tissues as well as it plays a key role in coordinating the immune response by concentrating immune cells in the lymph nodes. Male and female worms cluster, intertwining in the draining vessels just below the lymph nodes, and mate. Tissue samples of the cluster of worms can be viewed using the tissue culture microscope. A fertile female may produce approximately 1,000 larvae a day which can grow to three or four inches long. This filarial union can cause serious disease inasmuch as they most often position themselves in front of vessels draining liquid from the lymph nodes, causing an obstruction in the drainage. . This further triggers the surrounding tissues to fill with fluid and swell to elephantine proportions.

As the disease develops, the tissues in the swelling arms, legs or scrotum can die or become infected, turning black and oozing pus. These tissues can be examined under the tissue culture microscope. The fluid accumulation can likewise result to permanent disfigurement since the swollen limbs become solid masses with connective tissue, blood vessels and nerve endings. The solid mass can be seen clearly using the tissue culture microscope. Reducing the bulging tissue can require major surgery.

Gaining enough knowledge on how this particular parasite has adapted to humans may produce medical benefits. Worms can be viewed as foreign tissue transplanted into the human body. The worms can survive for years in the body as shown in the tissue samples examined in the tissue culture microscope. Discovering the reason why they do so may prove to be beneficial someday especially in the field of transplant surgery.