Possible links between biting aquatic insects, water quality and Buruli ulcer transmission

Oct 12 2005

A tropical skin disease nicknamed "the sore that heals in vain" wreaks both physical and social mayhem - mostly on children - yet its transmission is a mystery, one an Michigan State University (MSU) researcher and his recent research associate hope to solve.

Richard Merritt, chairperson of the Michigan State University Department of Entomology, and Eric Benbow, now at DePauw University in Indiana, are using a $2 million grant from the National Institutes of Health and National Science Foundation to investigate possible links between biting aquatic insects, water quality and Buruli ulcer transmission.

"It's called the 'mysterious disease' because nobody knows how it's transmitted," Merritt said. "So that's the real dilemma and we're just getting started trying to figure this disease out."

Scientists do know Buruli ulcer disease is cased by a bacterium, Mycobacterium ulcerans, found in tropical regions such as western Africa. They also know 70 percent of Buruli ulcer patients are children under 15 years old and for the last decade the number of infections is on the rise.

A Buruli ulcer infection begins with a painless raised nodule followed by a sore. Left untreated, the mycobacterium produces a toxin that destroys surrounding tissue, muscle and in some cases bone, leaving open wounds, or ulcers, and disfigured limbs, Merritt said. In many cases, amputation is the only option.

Antibiotics have shown some success in treating Buruli ulcer if caught in its early stages, but by the time patients normally seek medical attention it is too late.

"I was in an orphanage in Ghana where 60 percent to 70 percent of the kids had Buruli ulcer disease," Merritt said. "Some of these little kids' arms or legs are covered with ulcers and doctors can't do a skin graph because there isn't enough skin there to take. I was really touched by these kids."

Merritt, who is a specialist in aquatic and medical entomology, will investigate any possible role that biting water insects, like the creeping and giant water bugs, may have in the transmission of the disease.

If insects are transmitters of M. ulcerans, determining the way they transfer the disease agent is key. Merritt speculates the pathogen may be transmitted to humans from a direct insect bite. It's also possible biting water insects might be a reservoir for the bacterium to grow. The bacterium also may live in the water or attached to the surface of plants and infect humans by entering the body through scratches and cuts, Merritt said.

"Buruli ulcer has always been associated with water," Merritt said. "That's the critical thing. No matter where the disease is, there's always water around. Insects are thought to be involved. That's how I got in to this."

He and Benbow also will explore possible connections between land use, water quality and pollution, and the increasing rates of Buruli ulcer infections. It's possible M. ulcerans is a normal inhabitant of some tropical water bodies, Merritt said. He suggests man-made changes in water quality may be giving the bacterium a competitive advantage resulting in an increased presence.

Buruli ulcer also has economic impacts. Families must absorb the costs of medical treatment and may miss days of work to care for their sick children, Merritt said. For those whose bodies have been ravaged by the infection, the disease's effects are life long.

"Many people don't report their illness to their own village because they may be considered social outcasts," Merritt said.

Unraveling Buruli ulcer disease is a collaborative effort. Merritt hopes to establish a scientific partnership between MSU and Ghana. He and his research team are working closely with local Ghanaian Ministry of Health officials, the University of Ghana and the Noguchi Memorial Institute for Medical Research.

This spring, Merritt plans to invite one or more graduate students from Ghana to study with him at MSU. The goal is to equip people with the scientific expertise to battle the disease.

Merritt points out that there are many international students at MSU who are from countries with reported cases of Buruli ulcer, countries like Ghana, Benin and Togo.

"MSU has the opportunity to help mankind and in terms of the land-grant mission, we can help increase health and economic stability," Merritt said. "We want to give them something back. Training is one of the ways we can do that."

Merritt plans to return to Ghana in spring 2006 to continue his research and build strong relationships with the area villagers whose lives are affected by this disease.

"When villagers find out what we're doing and that we are trying to help them, they are very glad to see us," Merritt said.