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During the first few months of their lives, foals are highly susceptible to bacterial infections and toxins because of their immature immune system. Photo: Myrna MacDonald.

Study focuses on lung failure in foals

Last summer, I was part of a research group at the Western College of Veterinary Medicine (WCVM) that's working to gain a better understanding of why young foals often die of respiratory distress and lung failure.

During the first few months of their lives, foals are highly susceptible to bacterial infections and toxins because of their immature immune system. As a result, these young horses can quickly succumb to complications of sepsis (a systemic bacterial infection.)

A possible, though poorly described, complication is the development of acute lung injury (ALI) and/or acute respiratory distress syndrome (ARDS). In humans, ALI and/or ARDS can occur as a complication from sepsis or endotoxemia (bacterial toxins in the blood).

The two conditions cause fluid and white blood cells to accumulate in the lungs and reduce their function. As lung function fails, breathing becomes very difficult and oxygen exchange is compromised, which may lead to death. 

In horses, studies have found that ALI and ARDS can result from direct injury of the lung tissue — such as pneumonia or aspiration — or from indirect injury such as sepsis or trauma.

In foals, bacterial infections can result from a number of sources. One example would be a lack adequate maternal antibody transfer from the dam's colostrum — resulting in an immuno-compromised foal that's susceptible to bacterial infection. Other examples include bacterial inhalation, ingestion or access through the umbilical cord which can spread to the lungs.

Although ALI and ARDS have been recognized in veterinary medicine, little research has been done to describe the type of inflammation that occurs and the changes that take place in the lungs of septic foals.

During the summer of 2013, I learned more about these two conditions alongside Dr. Stacy Anderson, an equine veterinarian and surgeon who is working on her PhD program at the WCVM. Both of us are working under the supervision of Dr. Baljit Singh, a professor in the WCVM's Department of Veterinary Biomedical Sciences and the college's associate dean of research.

"We don`t recognize ALI as much in horses as in people since it is generally a less common problem clinically," says Anderson.

Although ALI and ARDS have been studied and defined in human medicine, these definitions cannot be strictly applied to all species, including horses. This is due to differences in lung composition and inflammatory processes.

"There is still a lot to learn about these diseases in horses and many questions left to answer," says Anderson. "We would like to discover why these diseases look different in horses than they do in people."

One theory is that the differences in immune response in horses may prevent the extreme lung damage that occurs in humans, adds Anderson. "Or is this difference simply due to the larger lung capacity and ability for the horses to compensate for the damage by maintaining the ability to exchange oxygen?"

My contribution to the project is to examine lung samples from 19 septic foals and six healthy foals between one day and 60 days of age.

By staining these tissue samples, we can visualize the physical changes in the lungs as well as factors contributing to the inflammatory process. I analyze the stained tissue sections and grade them to determine the degree and characteristics of inflammation seen in the lungs of affected compared to unaffected foals. These results will be compared to the medical history reports to more clearly define ALI/ARDS in young horses.

With this information, it may be possible to build a greater understanding of ALI/ARDS progression.

"In order to properly treat a problem, we need to know the process of the disease," says Anderson. "By characterizing these diseases they will be easier to diagnose which will allow for more aggressive treatment of septic foals."

Results of this project will hopefully help researchers gain a further understanding of how ALI/ARDS affects young horses — knowledge that may ultimately lead to improved diagnosis and treatment.

Leah Quanstrom of Edmonton, Alta., is a second-year veterinary student who participated in the WCVM's Undergraduate Summer Research and Leadership program in 2013. 
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