Cholera track may spark cure
IN THE laboratories of the National Institute of Communicable diseases (NICD) a killer stored for decades in sub-zero temperatures has finally given up the secrets of its death trail.
That killer is Vibrio cholera 01, the causitive organism of cholera, which claims tens of thousands of lives each year.
Each sample held in the laboratory was collected when cholera epidemics swept through the country.
These samples and thousands of others collected across the globe have allowed scientists to track the genetic trail of the disease as it spread across the globe.
This study, which was released on Thursday, analysed genomic data from 1 070 Vibrio cholerae populations from 45 African countries, over a period of 49 years.
What the scientists were tracking is the seventh pandemic of cholera that began in 1961, and moved through Asia, Africa, the Caribbean and Latin America and caused the deaths of between about 21 000 to 143 000 deaths per year.
The seventh pandemic was driven by a strain of Vibrio cholerae called 7PET.
Previous studies, say scientists, have been unable to provide such a detailed picture of the pathogen as it journeyed across continents.
“Our results show that multiple new versions of 7PET bacteria have entered Africa since the 1970s.
“Once introduced, cholera outbreaks follow similar paths when spreading across that continent.
“The results give us a sense of where we can target specific regions of Africa for improved surveillance and control,” says Dr François-Xavier Weill, first author on the African study and principal investigator from the Institut Pasteur.
The largest epidemic in history is continuing in Yemen where the number of cases is close to a million.
Dr Karen Keddy of the NICD, contributed to the local arm of the international study.
“In Asia, your endemic case numbers are larger, whereas in Africa it really does come in waves, cholera then disappears for a few years then another big outbreak, occurs then it disappears,” she says.
Earlier research of the 7PET strains even pinpointed the geological location where the disease left from when it disembarked for Africa from Asia.
This point is the Bay of Bengal, and scientists aren’t too sure why this is so.
Airline travel has also enabled the faster transmission of cholera around the globe.
South Africa hasn’t had any serious cholera outbreaks recently Keddy said, and this is thanks to good vigilance and a health-care system that has responded quickly when the disease strikes.
It is also a disease where patients recover remarkably quickly.
“This is such an easy disease to manage if you are just prepared for it,” says Keddy.
“Because you save lives through rehydration, you don’t need costly antibiotics because eventually the patient develops immunity.”
South Africa’s largest cholera outbreak in recent years happened in 2001 when there were more than 100 000 cases, according to Dr Juno Thomas, of the NICD, who was not part of the study.
Most of South Africa’s current cases of cholerae are caused by patients bringing the disease across the border unintentionally.
The majority come from Zimbabwe, and sometimes a patient will arrive from India with symptoms.
In 2008/2009 there was a cholera outbreak in Zimbabwe that spilled over mainly into Limpopo.
Doctors without borders personnel working in Musina, identified the first case and raised the alarm.
But by having a better understanding of how the disease spreads, Keddy believes health professionals will be given an edge in fighting the pathogen.
“If we can trace where cholera gets introduced, and how it gets introduced, if we can define how it gets into the environment and stays in that environment, then it will be so much easier to come up with campaigns.”
However more work needs to be done.