Once thought to be confined to tropical regions, Burkholderia infections are now surfacing closer to home. University of Florida Emerging Pathogens Institute member and UF College of Veterinary Medicine professor Apichai Tuanyok, Ph.D., explains how Burkholderia infections infect, evade and persist, and what can be done to stop them.
What follows has been edited for length and clarity.
What is Burkholderia, and what are the different species?
Burkholderia is a diverse bacterial genus with approximately 100 known species, including two main groups called complexes. The Burkholderia pseudomallei complex contains species that cause serious diseases like melioidosis and glanders, while the Burkholderia cepacia complex includes species that can infect both humans and plants. The B. cepacia complex is particularly aggressive in individuals with weakened immune systems or cystic fibrosis. Members of B. cepacia complex have a large genome of about 8,000 genes, compared to about 6,000 in the B. pseudomallei complex, ensuring survival in various environments like soil and water, alongside competing organisms.
The bacteria eventually adapted to mammal hosts after infecting plant and animal cells. Other species became plant pathogens by colonizing root systems and disrupting normal plant-microbe interactions.
What is melioidosis, and where is it commonly found?
Melioidosis is a severe tropical disease caused by B. pseudomallei, which can be transmitted through three different routes: Inhalation, ingestion and contact with contaminated soil.
Burkholderia species are frequently found in Southeast Asia and northern Australia.
What symptoms appear with melioidosis?
Symptoms can appear one to four weeks after exposure to B. pseudomallei bacteria.
A localized infection often looks like an ulcer or skin abscess. Abscesses can occur anywhere in the body, especially in the liver. Symptoms generally include fever and muscle pain. Once the bacteria enter the blood, if not treated promptly, they can cause severe complications like pneumonia, sepsis, organ failure and death. These conditions are more frequently seen in patients who have underlying risk factors like diabetes and kidney issues.
How do you diagnose and treat melioidosis?
The standard method for diagnosing most Burkholderia infections relies on a bacterial culture. If the culture is grown correctly, molecular tests can confirm if it’s B. pseudomallei. This can take four to five days. Tragically, patients often die while waiting during this vital time.
Melioidosis treatment has two phases for the acute infection due to the highly resistant bacteria. Preventing sepsis requires 14 to 15 days of intravenous antibiotics. The second phase aims to eradicate bacteria from tissues and cells, requiring a combination of oral antibiotics twice daily for 20 weeks.
Completing the full 20-week course can be challenging for the patient at home, but failing to do so worsens the problem overall, as it increases the risk of antibiotic resistance. That’s why the antibiotics, latency and relapse are all tied together.
What are some challenges in vaccine development?
My team and I are working on developing a solution for both animals and humans. The problem is that the vaccine we’ve been testing cannot provide long-term protection, although it can prevent acute infections.
Currently, the antibodies from the vaccine can only attack bacteria in the blood, but when the bacteria enter the tissue, the antibodies can’t penetrate it. That’s where our immune system has to step in, like T cells. We are trying to complement our vaccine with a certain antigen that we know can activate the tissue response. These two things would work in harmony, hypothetically.
Are there any emerging trends that suggest melioidosis or Burkholderia are becoming a greater concern in the United States?
Yes. With climate change, we’re seeing some recent local cases in the southern U.S. Specifically, we’ve seen cases in Mississippi, Texas and Georgia. It’s also not uncommon for people to accidentally import commodities from overseas that contain bacteria. Since the infection can remain latent in the body, it’s challenging to determine where the infection was acquired.
I’ve been investigating potential Burkholderia cases in Florida and elsewhere in the U.S. for almost 20 years now. One of the earliest indications that melioidosis might be present here came from a 2006 case involving an American Quarter Horse from Ocala admitted to the UF Large Animal Hospital. The horse died of a severe infection initially attributed to an unidentified member of the B. cepacia complex. My team reexamined tissue samples using genetic techniques. The results suggested that the pathogen was B. pseudomallei. This is why the scientific community needs to continue investigating, because there have likely been misdiagnosed cases that need reevaluation.
How do we prevent melioidosis and Burkholderia infections in the U.S.?
If we suspect melioidosis is maybe endemic in the southern states, we need to do environmental surveys, like soil and water, to confirm that.
Stricter import policies on commodities from melioidosis-endemic countries could help. In 2021, imported contaminated aromatherapy sold in large American stores caused four infections and two deaths. Monitoring for Burkholderia in the illegal exotic animal trade is also extremely important. This bacterium doesn’t discriminate.
From a One Health perspective, what research gaps do you think are the most important to close?
We know little about animal-to-human transmission, as few cases are observed. Surveillance needs to be developed since bacteria in soil and water can infect animals and humans. Zoonotic transmission rates are still somewhat unknown. That would be a good next step in the research.
Written by: Sydney Burge