Buruli ulcer is a disease caused by the bacterium Mycobacterium ulcerans, which can even cause skin necrosis. It occurs in Africa, South America, and the countries of the Western Pacific. Until now, it was not known how infection with this pathogen occurs. However, research by Australian scientists shows that mosquitoes are to blame.
Bacteria Mycobacterium ulcerans causes Buruli ulcer. In the first stage, this disease manifests itself as a painless lump. Later, however, it leads to necrosis of the skin and subcutaneous tissue, reaching deeper tissues. However, for decades, scientists have not known how infection with this pathogen occurs.
What causes this disease
According to research by Australian specialists, the results of which were published a few days ago in the journal “Nature Microbiology”, to infection Mycobacterium ulcerans comes through mosquito bites. Scientists took the species into account Aedes notoscriptus, appearing, among others, in Australia or New Zealand.
Buruli ulcer, discovered in Australia in the 1930s, has been reported in at least 33 countries around the world, mainly in tropical and subtropical regions – Africa, South America, as well as countries in the western Pacific. According to the World Health Organization (WHO), 1,370 new cases were reported worldwide in 2021. The disease can be treated with antibiotics if diagnosed early. Scientists didn’t previously know how bacteria spread from the environment to humans. Mosquitoes were suspected to be the culprit, but this was not confirmed. Until now.
Mosquitoes spread diseases
It is well known that mosquitoes transmit many other diseases to humans – including dengue, West Nile fever and malaria. However, these diseases are caused by viruses and parasites, not bacteria. Fleas, ticks and lice transmit various bacterial diseases to humans, but so far there have been no cases of this type of bacteria being transmitted by mosquitoes, said Tim Stinear, co-author of the study and director of the WHO Collaborating Center.
Scientists already knew that Buruli ulcer is a zoonotic disease, meaning it is caused by germs that are somehow transmitted between animals and humans. Mammals found in Australia, such as those of the pseudopane family, are the main reservoir M. ulcerans in southeastern Australia. However, it was not certain how the bacteria spread from animals to humans.
Between 2016 and 2021, Stinear and colleagues captured and studied more than 65,000 mosquitoes in the Mornington Peninsula region of southeastern Australia. They focused on the genre Aedes notoscriptustransmitting diseases in this region.
Field studies in Victoria indicated that mosquitoes may have been responsible for transmitting the virus during previous outbreaks in the state. Meanwhile, observations carried out in Cameroon showed that protective measures against mosquito bites, such as mosquito nets, can reduce the risk of infection.
Recently, there has been an increase in infections with this disease in south-eastern Australia. On January 18, the Victoria state authorities announced that in 2023, the highest number of recorded cases of Buruli in humans was recorded – 363.
How the discovery was made
To gather evidence to support the idea that mosquitoes spread M. ulcerans, scientists collected bacterial samples from the feces of pseudopod animals and from clinical samples from sick people. They then sequenced the genomes of these samples and compared them with those from the mosquitoes they studied.
They found that all samples had a genetic makeup M. ulcerans was identical. Additionally, human infections coincided with places where the mosquitoes were collected. Analysis of the mosquitoes’ blood also confirmed that they “fed” on both humans and opossum mammals, suggesting that the mosquitoes likely transmitted the bacterium from opossums to humans through their bites.
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