In spite of widespread vaccination efforts against whooping cough, the disease is on the rise around the world, even in developed countries. Scientists looking at a new type of treatment hope to turn that trend around.
Whooping cough remains a major cause of infant deaths worldwide. Each year thousands of children die from the highly contagious respiratory ailment.
Currently, there are no treatments specific to whooping cough, which is marked by uncontrollable, violent coughing fits that can make it difficult to breathe.
To fill this void, researchers from the University of Texas at Austin and other institutions are pursuing a treatment that uses two antibodies to block the toxin produced by the bacteria that causes whooping cough, Bordetella pertussis.
The treatment has only been tested in mice and baboons, but the researchers say that their results are encouraging.
Antibodies Provide One-Two Punch
The bacteria that cause whooping cough produce a variety of toxins and other compounds. In this study, researchers focused on one specific toxin that is thought to weaken the body’s immune response and increase the number of white blood cells.
The researchers identified two monoclonal antibodies that seem to bind to this toxin and block its activity.
“It gives this one-two punch to deal with the toxin,” study author Jennifer Maynard, PhD, an associate professor of chemical engineering at the University of Texas at Austin, said in a press release last year.
Antibodies are proteins produced by the immune system to identify and target bacteria and viruses in the body. The researchers used one antibody to bind to the whooping cough toxin and prevent it from attaching to healthy cells. The other kept the toxin from reaching its target inside healthy cells.
Together, this provided the animals with “instant immunity.”
The researchers chose to use two separate antibodies because one bound more tightly to the toxin and another provided the best blocking power.
The results were published online today in Science Translational Medicine.
Newborns Most at Risk
The Centers for Disease Control and Prevention (CDC) recommends that every infant receive a pertussis vaccine starting at two months. This is followed by additional shots at 4 months, 6 months, 15 to 18 months, and 4 to 6 years.
This vaccine is included in a single shot with vaccines for diphtheria and tetanus—collectively known as DTaP.
Vaccines work by stimulating the immune system to produce antibodies against pathogens, in this case the bacteria that cause whooping cough.
Infants cannot be given the DTaP vaccine earlier than 2 months because their immune system has not developed enough to create these antibodies. That leaves them unprotected during that time. But not entirely. Women can pass on some of their antibodies to their unborn child as well as to a newborn through breast milk. But to do so they must have high levels of whooping cough antibodies in their blood. That is why the CDC recommends that all pregnant women receive the whooping cough vaccine in their third trimester.
Even that may not be enough to protect every infant from the disease. In one study, only 14 percent of women on Medicaid in Michigan received the TDaP vaccine during their first pregnancy. Also, not every infant will receive enough antibodies, even from vaccinated mothers. And the level of antibodies in an infant’s blood can drop quickly after birth.
Continuing Rise in Cases
Parents who skip vaccinating their infant for whooping cough put their child at risk for developing the illness and exposing immune compromised people to it.
But some studies also say the vaccine is no longer as effective as it once was, in part because the bacteria has gradually mutated.
Cases of whooping cough are on the rise, in part because of lower vaccination rates and effectiveness, and in part because doctors have gotten better at detecting it.
In 2012, there were 20 deaths related to pertussis in the United States, most of them in infants younger than 3 months of age. That year also saw the largest number of cases since 1955.
The development of new vaccines that better target the current whooping cough bacteria will help, but they may be years away. The researchers see their treatment as eventually filling in the gap for infants that are not completely protected against whooping cough.
“The neutralizing antibodies described here could provide a complementary therapeutic strategy when maternal immunization fails,” they wrote in the paper.
Further studies of the toxin-blocking antibodies are needed. Researchers plan on doing additional research in newborn baboons. If those go well, clinical trials in people will be next.