Vaccine shows promise against tularemia

By Nelson Sigelman - January 18, 2007

A tularemia vaccine developed with the cooperation of Vineyarders may provide protection in the future from a deadly bacterium that is the cause of still unexplained outbreaks of disease on the Island and is a prime candidate for use as a bioterror agent.

Epivax, a Rhode Island based biotechnology company, announced Monday that it has developed a promising tularemia vaccine candidate identified by the name TuliVax.

According to a press release, animal studies conducted at Rhode Island Hospital showed that TuliVax protected a majority of mice from a lethal exposure to the F. tularensis bacterium that causes tularemia, sometimes called rabbit fever.

After receiving a grant from the National Institutes of Health to develop a tularemia vaccine, Epivax selected Martha's Vineyard as a research site because it is one of the few places where the air-borne form of the disease has been seen with any frequency. Researchers wanted to study the immune response to natural tularemia infection and use that information to develop a vaccine that mimics those responses.

After a screening of likely candidates, 26 Islanders participated in the study by providing blood samples to Epivax.

This week Julie McMurray, Epivax's senior project manager, said that only human vaccine trials could determine if the vaccine will protect people, but that based on the evidence the company is hopeful.

On Sunday company representatives will present the results of their research to the Island public. Ms. McMurray said the presentation from 7 to 8 pm in the Baylies Room at the Old Whaling Church in Edgartown would be used to describe what the company learned from the blood samples, the path to eventual licensure of a vaccine and to answer questions.

Despite promising results, even under ideal circumstances a government-approved vaccine is likely still years away. Ms. McMurray said that as an example, the turnaround from research to approval for a Hepatitis B vaccine was one of the shortest and that took more than 15 years.

Deadly speed

Ms. McMurray said what makes Tularensis different from other bacteria is its ability to quickly subvert and overwhelm the immune system. "People that have tularemia go from ostensibly healthy to critically ill within hours or at most days," she said. "This rapid disease progression makes tularensis a rather difficult bug to protect against and very few experimental vaccines have even made it to this stage of protecting mice."

She said that TuliVax was tailor-made for humans using specialized software developed by Epivax and that most experimental vaccines fail before this stage. Another promising aspect, she said, is that the mice demonstrated no ill effects from the vaccine, which is made up of small synthetic parts that mimic the presence of tularensis bacteria but neither the bacteria nor substances derived from the bacteria are actually used in the vaccine.

According to the Centers for Disease Control and Prevention (CDC), about 200 cases of tularemia in humans are reported each year in the United States.

A CDC report said that tularemia is endemic to Martha's Vineyard. The worst occurrence was in the summer of 2000, when there were 15 cases confirmed on the Island and one death, the first confirmed tularemia death in the state since 1996.

In recent years, an unusually high number of pneumonic (airborne) tularemia cases have been diagnosed on the Vineyard. Local, state, and federal medical experts have been unable to provide any solid explanation for the outbreak of tularemia. The Vineyard experienced six confirmed cases of tularemia in the summer of 2006.

The pneumonic form of the disease is the most dangerous and if left untreated has a mortality rate as high as 60 percent. Tularemia, in aerosol form, is considered a possible bioterrorist agent.

Small wild animals, mainly rabbits, carry the bacteria that cause the disease. Pneumonic tularemia is thought to occur when bacteria from an infected animal becomes airborne when the dead animal or the ground around it is stirred up during mowing, brush cutting, or excavating. During past Island outbreaks, landscapers and brush-cutters have been advised to wear masks while working outside.

According to the Centers for Disease Control, people can get tularemia many different ways: by being bitten by an infected tick, deerfly, or other insect; by handling infected animal carcasses; by eating or drinking contaminated food or water; or by breathing in the bacteria.

Symptoms of a tularemia infection are similar to those of a bad case of flu. They may include fever and/or respiratory symptoms; chest congestion, tightness, or pain; lethargy; cough; or chills.

The characteristics of tularemia have also thrust it onto the front lines in the war on terror. Scientists around the world consider the bacterium a prime candidate for use as a bioterror agent because it occurs naturally and can be cultured.

Tularemia is also the subject of worldwide study. In November 2006 researchers and students from around the world gathered at the Marine Biological Laboratory in Woods Hole for the Fifth International Conference on Tularemia.