Stopping Salmonella

As a veterinarian in Sudan, his home country, Amin Fadl worked with large poultry producers in the Khartoum area to optimize the health and growth of their flocks. In 1993, he moved to the United States to attend the University of Connecticut, where he earned his master’s and doctoral degrees in microbiology. Now an assistant professor of animal sciences at CALS, Fadl brings his various experiences to bear in the classroom, where he teaches “Animal Science 320: Animal Health and Disease Management,” and in the lab, where he is developing a poultry vaccine against salmonella.

Let’s start with salmonella. What is it and how does it get in our food supply?

Salmonella is one of the major foodborne pathogens. It’s a zoonotic pathogen, which means it can be passed between humans and animals. Humans mostly get infected by eating contaminated meat from infected animals. Unfortunately, a significant number of chickens in our nation’s poultry operations are carriers of this pathogen. They have it in their intestines but don’t show any symptoms or signs of sickness. So during meat processing, salmonella from the intestines can sometimes contaminate the carcass, the meat. As for eggs, salmonella either can be on the outside, on the eggshell, or inside, in the yolk. A significant proportion of eggs are contaminated, so that’s why people always recommend that eggs be cooked properly before eating.

How big of a problem is this?

It’s big. According to the Centers for Disease Control and Prevention, there are about two million cases of salmonella infection in humans every year, but many people just have minor abdominal cramps so they don’t go to the hospital. About 43,000 people actually go to the hospital and provide samples that confirm salmonella infection.

And it can be a big problem for poultry producers, too. Consider last summer’s salmonella outbreak that was linked back to an Iowa egg-producing farm. Many millions of eggs had to be recalled, so that was a huge economic loss. And not only that, but production on this farm was basically stopped for a significant period of time—months—until regulators made sure that they had cleaned everything, sanitized everything and figured out the source of the contamination.

Overall, salmonella is believed to have a total economic cost of more than $1 billion dollars per year.

How would an animal vaccine help?

The whole issue here is how we are going to reduce salmonella outbreaks in humans. Our approach is to stop the infection at the source. Before chickens are harvested, we want to make sure that they are free of salmonella. One way to do this is by administering a vaccine that inhibits the colonization of salmonella in the intestinal tract. This breaks the chain of infection at the source.

How does your vaccine work?

Our vaccine is a weakened form of the pathogen. It’s called a live attenuated vaccine. To make it, we deleted a gene from the salmonella genome known as gidA, which controls the production of a suite of disease factors and co-factors. You can immunize mice with our mutant strain, and then challenge the animals later with a lethal dose of regular salmonella and nothing happens. They stay healthy.

Now we need to test it in chickens to make sure that this vaccine is indeed capable of blocking or reducing the colonization of salmonella in the intestinal tract of these animals. If it does, we can look to take it to the next level.