A recent study by Bournemouth University’s researchers in England suggests that El Niño Southern Oscillation (ENSO) has a strong link with Buruli ulcer outbreaks. The research, published in the journal Emerging Microbes and Infections reported that complex changes in rainfall patterns including drought, with later periods of extreme rainfall events and atmospheric anomalies driven by ENSO affect the spread of Buruli ulcer in French Guiana, South America region where the disease is endemic.
Buruli ulcer is considered one of the 17 neglected tropical diseases registered by the World Health Organization (WHO). It is caused by Mycobacterium ulcerans, an organism which belongs to the family of bacteria that causes tuberculosis and leprosy. Infection caused by this organism leads to destruction of skin and soft tissue with large ulcers, and may cause permanent disability or even death.
WHO has reported cases of Buruli ulcer in 33 countries in Africa, America, Asia and the Western Pacific. Most of them have occurred in tropical and subtropical regions, but have also been outbreaks in Australia, China and Japan. Each year, the Organization reports approximately 6000 cases.
Currently, it is not well known the transmission mechanism, but the most accepted hypothesis is that the bacillus reproduces in water, as reported cases are more frequent in areas near floodplain, plus among people who have being in contact with rivers, swamps and ponds.
ENSO refers to the effects of a band of Pacific Ocean surface temperatures which are anomalously warm or cold (called ‘El Nino’ and ‘La Nina’) and can cause increase or decrease in rainfall incidence in the western coast of South America. The study authors noted that these environmental changes have become a focus of attention, because while currently cases of Buruli ulcer occur only in parts of Latin America, weather conditions predicted for the coming years would favor the spread of the pathogen in all the territory.
Aaron Morris, lead investigator on the research project as a part of his PhD at Bournemouth University, said; “Understanding how infection levels respond to climatic factors is hugely important, particularly with poorly understood, emergent diseases such as Buruli ulcer. These links help us shed light on their ecology and enable us to more accurately predict outbreaks. They are also vital in understanding how climate change will affect the dynamics and emergence of pathogens in the future.”
According to Morris, the reduction in rainfall in Guyana formed stagnant water bodies, causing a more favorable environment for M. ulcerans spread. Then periods of heavy rain may have flooded the stagnant water bodies, favoring people’s contact with the bacillus. He also explained that by understanding how weather relates to the number of Buruli ulcer cases, it may be possible to identify the exact routes of transmission, predict outbreaks more accurately and adjust the monitoring of local populations.
On the other hand, according to Vidal Haddad Junior, professor at the Faculty of Medicine of the Sao Paulo State University (UNESP) in Brazil, changes in environmental parameters driven by El Niño may favor the occurrence of the bacillus, but would not be a determining factor for spread the disease.
Junior also said that another possible cause of spread would be the proliferation of water bugs, living in ponds and stagnant waters, ideal environment for the bacillus reproduction. Junior added that the research is scientifically sound, as it is expected that high precipitation increases watercourses, but the disease should be studied further.
Also, the Brazilian researcher pointed out that now Buruli ulcer is gaining attention and is a breakthrough, because it is one of the most neglected tropical diseases, and epidemiological data in endemic countries are difficult to obtain.
Through: Scidev.net, WHO
