Tuesday, March 27, 2012

Whooping Cough and Its Vaccine

The list of bacterial infections becoming ever more difficult to cure due to development of multi-drug resistant forms of the pathogens may now include a new name.  Strains of the bacterium responsible for the childhood disease Whooping Cough have developed new genetic identities capable of evading the vaccine currently used to prevent the disease.

Whooping Cough, also known as Pertussis, is caused by the bacterium Bordetella pertussis and most often afflicts infants and young children.  Efforts to breathe during the violent coughing fits are accompanied by a characteristic "whooping" noise.  Antibiotics are often ineffective by the time the disease is diagnosed, which is why prevention through vaccination is the most effective treatment.  Whooping Cough has increased in frequency in recent years partially due to fading levels of immunity in older children and adults who were vaccinated years ago, which is why adults who care for young children are encouraged to get "booster shots" of the vaccine.  Some of the increase in Whooping Cough frequency may also be attributable to falling vaccination rates in infants. 

Lower rates of vaccination are likely a response to the scientifically unfounded fears of a link between autism and vaccines.  As unfounded as those fears are, the public outcry inspired the development of a different type of Whooping Cough vaccine.  The traditional vaccine, developed in the 1940s, includes inactive B. pertussis cells.  Including the whole cell in the vaccine provides the body with more information it can use to recognize live bacteria in the future, should they ever enter the body and try to cause disease.  The newer vaccine, developed in 1991, includes pieces of B. pertussis that make it unique from any other type of bacteria.  Including pieces rather than the whole cell reduces the already incredibly low risk of vaccine complications like high fever and brain swelling, but it also reduces the information available for the body to use to recognize B. pertussis in the future. 

Now, new strains of B. pertussis may be better able to cause disease throughout the population by altering one of those pieces.  This alteration means that the pieces present in the vaccine are no longer representative of the strains of B. pertussis the body is likely to encounter.  Thus, the vaccine is not effective in preventing disease.

The emerging strains of B. pertussis identified by a research team from the University of New South Whales were collected between 2008 and 2010 in Australia.  These strains contain slight differences in the portion of the DNA responsible for encoding pertactin, a protein on the outer surface of the bacterial cell.  This new form of pertactin may not be recognized by the immune systems of individuals given the vaccine developed using pieces of B. pertussis or of individuals whose immunity has faded since receiving the vaccine years ago.

The change in Whooping Cough vaccines provides an example of the influence public demand can have on public health.  Now that the disease is reemerging as a concern, the public has an opportunity to support advances in vaccine technology motivated by a legitimate need for disease prevention rather than misled fear of science.  Studies identifying the new emerging strains of infections like Whooping Cough can provide "mug shots" of these pathogens so that both the public and the vaccinologists better understand what they are facing.

The researchers report their findings in the March edition of the Journal of Infectious Diseases.  More information about the types of Whooping Cough vaccines is available from the Centers for Disease Control

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