Bordetella pertussis bacteria – Credit CDC
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Although humans may like to believe that we represent the pinnacle of evolution - when you look at an organism’s ability to change, adapt, evolve . . . and to survive as a species – viruses and bacteria have us beat badly.
Not only have they been around far longer than humans, they are likely to be here long after we are gone.
With replication rates that provide for new generations every few hours – instead of every couple of decades – they possess an evolutionary nimbleness that allows them to adapt quickly to a changing environment.
Antibiotics, antivirals, and vaccines can temporarily hold these organisms at bay – but in their 70 years or use – only two diseases have been officially eradicated (smallpox and Rinderpest) from the globe.
None of this is to denigrate these miracle drugs, as they have saved countless lives and reduced untold misery, over the years.
But bacteria and viruses are moving targets, and our vaccines and antibiotics must constantly change to keep up with them.
Illustrative of the effect vaccines can have on disease rates is the following chart showing the number of Pertussis cases (whooping cough) in California over the past 60 years.
The dramatic drop in Pertussis - which began in the early 1950s – closely follows the introduction of the first whole-cell pertussis vaccine combined with diphtheria and tetanus toxoids (DTP) was introduced in the mid-1940s.
Nationwide, in the 1940s, about 160,000 cases of Pertussis were recorded, and the illness claimed about 5,000 lives.
By 1976 the number of reported cases in the country reached a record-low of 1,010 cases, a decrease of 99%. But over the past decade the number of cases has steadily risen, and in 2010 21,000 cases were reported.
The reasons for this recent rise are believed to include lower vaccination uptakes, the move away from whole cell pertussis vaccines to safer – but less broadly protective - acellular vaccines in the late 1990s, and evolutionary changes in the Bordetella pertussis bacteria.
Which bring us to a story out of Australia, where a new strain of Pertussis (Whooping Cough) is gaining ground – one that is not controlled by the current vaccine.
First the study which appears in the Journal of Infectious Diseases, then I’ll be back with a press release from the University of New South Wales, with more details.
Newly Emerging Clones of Bordetella pertussis Carrying prn2 and ptxP3 Alleles Implicated in Australian Pertussis Epidemic in 2008–2010
Sophie Octavia, Vitali Sintchenko, Gwendolyn L. Gilbert, Andrew Lawrence, Anthony D. Keil, Geoff Hogg and Ruiting Lan
Abstract
Australia is experiencing a prolonged epidemic of pertussis that began in 2008. A total of 194 Bordetella pertussis isolates collected from 2008 through 2010 were typed by single-nucleotide polymorphism (SNP) analysis, by multilocus variable number tandem repeats analysis, and by fim3, prn, and ptxP sequence analyses. Strains with 2 closely related SNP profiles carrying prn2 and ptxP3 from the recently emerged SNP cluster I predominated. The data suggest increasing selection among the B. pertussis population in Australia in favor of strains carrying prn2 and ptxP3 under the pressure of acellular vaccine–induced immunity.
This from the University of New South Wales.
Sharp rise in cases of new strain of whooping cough
21 March 2012
Australia’s prolonged whooping cough epidemic has entered a disturbing new phase, with a study showing a new strain or genotype capable of evading the vaccine may be responsible for the sharp rise in the number of cases.
A team of Australian scientists, led by the University of New South Wales (UNSW), believe this emerging new genotype (called prn2-ptxP3) of the Bordetella pertussis bacterium may be evading the protective effects of the current acellular vaccine (ACV), and increasing the incidence of the potentially fatal respiratory illness, according to the study published in The Journal of Infectious Diseases.
The new genotype also has been detected in other countries, suggesting it has the potential to spark epidemics elsewhere and should be closely monitored, the researchers warn.
“The prolonged whooping cough epidemic in Australia that began during 2008 has been predominantly caused by the new genotype of B. pertussis,” said one of the study authors, Associate Professor Ruiting Lan, of the UNSW School of Biotechnology and Biomolecular Sciences.
“The genotype was responsible for 31 percent of cases in the 10 years before the epidemic, and that’s now jumped to 84 percent – a nearly three-fold increase, indicating it has gained a selective advantage under the current vaccination regime.
The success of the Pertussis vaccine over the past 5 decades is undeniable, and hundreds of thousands of young lives have been saved because of it.
But as with any vaccine, antibiotic, or antiviral – victory over any pathogen is generally fleeting – and new techniques must be developed if we are to wage this never ending battle against the evolutionary process.
