Uncovering the genetics of a foul disease
28 March 2019
Researchers have been investigating the genetic components of European foulbrood (EFB), one of the major pathogens of honey bees (Apis mellifera).
Pollinating insects are crucial for global food security, the economy and ecology of the planet. Throughout the 20th century, scientists have recorded a global decline in insect pollinators, citing various issues such as climate change, habitat loss and disease.
EFB is caused by the bacteria Melissococcus plutonius. The bacteria was first characterised in 1912 by Gershom F. White, and the disease affects honey bee colonies worldwide.
Honey bee larvae become infected by eating food contaminated with the bacteria. The bacteria then reproduce and multiply in the guts of the larvae and compete for food, eventually leading to the larvae dying of starvation. Cases vary in severity, but in very severe cases, the bacteria can spread throughout the colony, killing larvae until the colony collapses. There are treatment options, but the disease is incredibly infectious and in approximately 50% of cases the hive has to be destroyed to prevent further spread.
As worker bees remove diseased or dead larvae from the hive very quickly, the infection can be difficult to spot, but visible symptoms include larvae curling into a distorted, unnatural shape within their cells and turning yellow, then brown and finally turning black as they decompose. The name ‘foulbrood’ comes from the foul smell that can occur in severe outbreaks.
EFB is one of the most common diseases affecting honey bee colonies in the UK with nearly 300 outbreaks found in 2018. As honey bees are significant pollinators, this disease is of substantial ecological and economic concern.
If an outbreak isn’t severe, infected larvae can survive infection, however they are carriers of the bacteria, and can spread the disease through their natural movement. Researchers have estimated that a third of colonies in apparently healthy apiaries may include adult bees carrying the bacteria. As it is thought that EFB outbreaks are closely linked to colony stress, these apparently healthy colonies could experience an outbreak if put under stressful conditions such as a change in climate, poor nutrition or even if the hive is moved.
The cause of the variety in severity of outbreaks is unclear, and Nicola Burns, researcher at the University of York has been studying the genetic components of EFB that effect virulence and variability in outbreak severity, specifically genes related to biofilm formation, toxin production and antibiotic resistance.
“It is really important to understand the genetic component of virulence because it helps predict how an infection may progress, for example, if it will be severe and deadly or not” Nicola said.
Nicola’s research involved working with samples of diseased larvae sent to the National Bee Unit by bee inspectors and beekeepers. Nicola has used this collection in her research, identifying potential genes for various virulence factors and how they differ in various strains of the bacteria. In the ongoing research Nicola intends to test these hypothesised genes and differences in strains, hoping to be able to predict disease severity more reliably.
Nicola says “If disease severity can be reliably predicted from strain type, gene content or another genetic marker then treatment strategies will be better informed. A better overall understanding of M. plutonius should help to improve the control or treatment of EFB in future.”
Nicola’s research is a CASE PhD project funded by the BBSRC and the National Bee Unit, with additional generous funding from Bee Diseases Insurance Ltd.
Nicola Burns will present her data at the Microbiology Society Annual Conference in Belfast. Her poster: ‘Genetic studies of European foulbrood: virulence, persistence and antibiotic resistance’ will be part of the Non-Human Pathogens session and will be available to view on Monday and Tuesday in Hall 1D.
Image: iStock/Oleksandr_Kolos.
