Genetic Mutation May Explain Increase in U.S. Whooping Cough Cases

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An old disease is making a comeback, possibly due to a bacterial mutation. Seventeen states and Washington D.C. are reporting an increase in whooping cough this year. It’s an epidemic in Texas, on pace to be the worst in half a century [1]. The very young are most at risk.

Whooping cough

Whooping cough or pertussis is a bacterial infection caused by Bordetella pertussis. It’s a highly contagious disease that clogs the airways with mucus, causing severe bouts of coughing. Pertussis symptoms include uncontrollable, violent coughing which makes it hard for the patient to breath. The patient then needs to take deep breaths, which produces a whooping sound, hence the diseases’ nickname “whooping cough.”

Early symptoms, which last approximately one to two weeks, include a runny nose, low-grade fever, a mild, occasional cough and a pause in breathing called apnea. Later, patients can exhibit the rapid coughs and high pitched “whoops,” vomiting and exhaustion after coughing. People remain contagious up to two weeks.

Whooping cough is more common in infants and young children, and can be fatal especially for children under 1 year of age.

A series of five doses of pertussis vaccine (called DTaP, the child pertussis vaccine) begins at two months after birth and is completed by 4-6 years of age. Preteens going to the doctor for their regular check-up at age 11 or 12 years should get a booster vaccine, called Tdap.

Despite widespread vaccination, pertussis has persisted in vaccinated populations and is one of the most prevalent vaccine-preventable diseases.

Re-emergence of whooping cough

In 2012, the Centers for Disease Control and Prevention (CDC) declared it the worst year for whooping cough in nearly 60 years. More than 41,000 cases were reported in 2012. Compare that to the 9,771 cases reported ten years ago in 2002 [2]. In fact, between 2002 and 2012, there has been, on average, over 16,000 more cases every year than between 1970 and 2002, a 400% increase!

So far in 2013, 17 states are reporting an increase in cases of whooping cough compared with the same time during 2012, including Alaska, Arkansas, California, Colorado, Florida, Georgia, Louisiana, Montana, Nebraska, Nevada, North Carolina, Ohio, Oklahoma, Rhode Island, South Carolina, Tennessee, and Texas.

Indeed, it’s an epidemic in the state of Texas; there have been more than 2,100 cases this year and 2 infants who were too young to receive the vaccine have died.

Texas isn’t the first pertussis epidemic in the United States. Last year, Washington state declared a pertussis epidemic.

Genetic mutation to blame?

Concerns about whooping cough outbreaks have focused chiefly on the loss of immunity associated with the acellular vaccine, which was licensed for use in 1996 to minimize the risk of adverse events associated with whole-cell pertussis vaccine [3].

However, the recent rise in whooping cough cases may be caused by a genetic mutation of the bacteria, according to new findings published earlier this year in the New England Journal of Medicine [4].

Researchers at St. Christopher’s Hospital for Children in Philadelphia, Pennsylvania collected bacterial samples from 12 patients with whooping cough. In 11 cases, they found that the pertussis bacteria was no longer producing a cell surface protein called perlactin — one of three elements the body’s immune system uses to identify and fight the disease.

According to senior author Alan Evangelista, Ph.D., Director of Microbiology at St. Christopher’s Hospital for Children [5], the organism has adapted to evade one part of the immune system:

This particular [pertussis strain] is missing a surface protein. There’s a mutation that stopped making one of the targets. Usually the vaccine has three targets it goes after and this new strain only has two of the targets.

While the current pertussis vaccine will still work, it may not be as effective. The scientists have called for studies of isolates from geographically distinct U.S. regions to determine whether the finding is a local event or represents a more widespread shift in pertussis strains.

The researchers write that “an understanding of the epidemiology and virulence of pertactin-negative variants is crucial to developing the next generation of pertussis vaccines.”

What should you do?

What can you do to protect your kids from whooping cough?

Make sure the kids are up-to-date with pertussis vaccinations. Even diminished vaccine protection is better than nothing, and typically those who are vaccinated have milder cases.

Protect yourself. Adults should get a whooping cough booster shot so they don’t spread the disease.

Keep your kids away from those who are sick. Pertussis is spread through coughing or sneezing.

Watch for symptoms. Whooping cough typically starts with cold-like symptoms that can include a runny nose, congestion, low-grade fever and a mild cough. Infants may have a pause in breathing, called apnea. If you think your child might be sick, see a doctor immediately. Whooping cough is treated with antibiotics, and the earlier they can be given, the better.