eradication of tsetse flies through nuclear technology [FW]

["Franta, Jaroslav" <frantaj@AECL.CA>]

The Globe and Mail, Wednesday, February 20, 2002

http://www.theglobeandmail.com/index.html

Canada aids fight against tsetse fly

By KRISTA FOSS

Source: Department of Microbiology and Immunology, University of South Carolina, School of Medicine

 

Canadian expertise has equipped the war against sleeping sickness in sub-Saharan Africa with a new, highly effective weapon: an army of male tsetse flies neutered through nuclear technology.

The new science is so promising that the Organization of African Unity has announced an international offensive against the parasite-laden insect, which costs some of the continent's poorest nations more than $4-billion in economic losses each year.

As many as 500,000 citizens a year are infected with sleeping sickness, and the mortality rate is 80 per cent.

Tsetse flies, which thrive in Africa's fertile, moisture-rich regions, are not huge in number and don't reproduce quickly. But the insect is ideally suited to carry a single-cell parasite called a trypanosome, which attacks the blood and nervous system of humans and animals.

In the 37 impoverished sub-Saharan countries where the fly is endemic, farmers have been limited to tending less productive but parasite-resistant animals, or to cultivating arid, marginal land where tsetse flies can't survive. Infected people have been stuck with drugs that are toxic and difficult to administer, and there is little prospect of an effective vaccine.

To make matters worse, the parasite is showing signs of drug resistance at the same time that tsetse fly populations are rebounding in regions where they were once under control.

A successful experiment on the island of Zanzibar, off the coast of Tanzania, may change all that.

Eight years ago, Canadian entomologist and Saskatchewan native Arnold Dyck joined the International Atomic Energy Agency in Vienna to study the possibility of using irradiation on the tsetse fly.

Dr. Dyck had already used the procedure, known as the sterile insect technique, to lower the population of codling moths taking an expensive bite out of the apple-and-pear belt of Summerland, B.C.

The technique involves giving male insects a dose of gamma-ray radiation that renders them infertile.

When millions of these sterile males are released and reproduce with females, the resulting eggs or larvae do not develop.

"You use what is called an overflooding ratio; that is, you release more sterile insects than those that are wild, so the sterile males outnumber wild ones 10 or 20 to 1, in order to overwhelm the mating process," Dr. Dyck said from Vienna yesterday.

"Over successive generations the whole population gets lower and lower and may eventually be eradicated."

Delivering disease

Trypanosomes are types of parasites which can cause diseases such as sleeping sickness (infects humans), and nagana (infects cattle, horses, antelope and camels). The tsetse fly carries the disease by biting an infected host and carrying the parasite with it until it infects whatever human or animal it bites next.

 

1. The parasite multiplies in the blood, lymph nodes and spinal fluid of the host.

2. When a fly feeds on the blood of an infected host the parasite is ingested.

3. The parasitic cells multiply in the fly's midgut.

4. The parasite migrates to the fly's salivary glands and multiplies further, becoming infectious.

5. The parasitic cells in the fly's salivary glands are injected into the host's blood when the fly feeds.