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Scientists track evolution and spread of deadly fungus, one of the world’s major killers

3 May 2011

New research has shed light on the origins of a fungal infection which is one of the major causes of death from AIDS-related illnesses. The study, published today in the journal PLoS Pathogens, funded by the Wellcome Trust and the Biotechnology and Biological Sciences Research Council (BBSRC), shows how the more virulent forms of Cryptococcus neoformans evolved and spread out of Africa and into Asia.

Cryptococcus cyst from a brain biopsy. Credit: Kayser, Wellcome Images

Cryptococcus cyst from a brain biopsy.
Credit: Mike Kayser, Wellcome Images

Cryptococcus neoformans is a species of often highly aggressive fungi. One particular strain of the fungus - known as Cryptococcus neoformas variety grubii (Cng) - causes meningitis amongst patients with compromised immune systems following HIV infection. There are believed to be up to a million cases of cryptococcal meningitis each year, resulting in over 600,000 deaths. Infection with the fungus, which invades the central nervous system, is treated with a life long therapy of antifungal drugs, which can have highly unpleasant side effects.

Sitali Simwami and Dr Matthew Fisher from Imperial College London, together with colleagues from St Georges, University of London, Naresuan University, Thailand, and the CBS Fungal Biodiversity Centre, The Netherlands, used genetic sequencing techniques to compare the genetic diversity of Cng in 183 samples taken from the clinic and the environment in Thailand against the 77 samples from a global database. Thailand has an emerging HIV epidemic and nearly one in five HIV-infected patients are affected by cryptococcal infection.

"Cryptococcal meningitis kills hundreds of thousands of people each year, almost as many as malaria, yet gets little attention," explains Dr Fisher. "We know very little about where it originated from and how it evolved. If we can track its evolution and diversity, then we can begin to understand where the pathogen originates from, how it infects people and how it adapts to become more - or less - virulent. This information will be valuable in helping us identify potential therapeutic targets in the future."

The researchers found that Cng in Thailand exhibits significantly less genetic diversity in comparison to other areas of the world, especially Africa where many different lineages of the pathogen occur. This suggests that populations of the fungus in Africa will have a wider spectrum of virulent strains and higher rates of adaptation to antifungal treatments, implying that clinicians need to pay particular attention to the risk of drug-resistant forms of the fungus here.

Their analysis also suggested that the pathogen was introduced from Africa to Asia at some point within the last 7,000 years. Many human infectious diseases are thought to have emerged within the last 11,000 years, following the rise of agriculture and domestication of animals. In particular, it supports the idea that the pathogen was imported via infected pigeons, which were domesticated around 5,000 years ago. The common pigeon, which originated in Africa, is considered to be a carrier and potential spreader of the fungus, its faeces being a common environmental source of Cng.

ENDS

Notes to editors

Simwami, SP et al. Low diversity Cryptococcus neoformans variety grubii multilocus sequence types from Thailand are consistent with an ancestral African origin. PLoS Pathogens; April 2011. For more information visit www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1001343.

About the Wellcome Trust

The Wellcome Trust is a global charitable foundation dedicated to achieving extraordinary improvements in human and animal health. It supports the brightest minds in biomedical research and the medical humanities. The Trust's breadth of support includes public engagement, education and the application of research to improve health. It is independent of both political and commercial interests.  www.wellcome.ac.uk.

About Imperial College London

Consistently rated amongst the world's best universities, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 14,000 students and 6,000 staff of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve global health, tackle climate change, develop sustainable sources of energy and address security challenges.

In 2007, Imperial College London and Imperial College Healthcare NHS Trust formed the UK's first Academic Health Science Centre. This unique partnership aims to improve the quality of life of patients and populations by taking new discoveries and translating them into new therapies as quickly as possible. www.imperial.ac.uk.

About BBSRC

BBSRC is the UK funding agency for research in the life sciences. Sponsored by Government, BBSRC annually invests around £470M in a wide range of research that makes a significant contribution to the quality of life in the UK and beyond and supports a number of important industrial stakeholders, including the agriculture, food, chemical, healthcare and pharmaceutical sectors.

BBSRC provides institute strategic research grants to the following:

  • The Babraham Institute
  • Institute for Animal Health
  • Institute of Biological, Environmental and Rural Sciences (Aberystwyth University)
  • Institute of Food Research
  • John Innes Centre
  • The Genome Analysis Centre
  • The Roslin Institute (University of Edinburgh)
  • Rothamsted Research

The Institutes conduct long-term, mission-oriented research using specialist facilities. They have strong interactions with industry, Government departments and other end-users of their research.


External contact

Craig Brierley, Senior Media Officer, The Wellcome Trust

tel: 02076 117329