The genetic secrets of a misnamed microbe could help ease a lung condition that affects hundreds of millions of people, says microbiologist Timothy Murphy.
I’ve been thinking about an interesting organism lately, an organism that illustrates some basic principles in science-based medicine.
The organism is called Haemophilus influenzae (H flu), a gram-negative bacterium discovered in the late 19th century. H flu has a great story, both in historic and modern times.
Sequencing the genome of bacterium Haemophilus influenzae, reported in May 1995, demonstrated for the first time that random “shotgun” sequencing could be applied to whole genomes with speed and accuracy.
A new study reviewing women of reproductive age in England and Wales from 2009 to 2012, found that women who were pregnant were more likely to be infected with the bacterium Haemophilus influenzae, which in turn leads to a higher risk for premature birth and stillbirth.
When I was a pediatric resident in the early 1980s, I cared for many children who were gravely ill as a result of Haemophilus influenzae Type b (Hib) infection. "H. flu" was once the most common cause of bacterial meningitis (and acquired intellectual disability) in children younger than age 5. But, after the introduction of Hib vaccines during the mid-1980s, Hib cases in this age group dropped by more than 99 percent.
Haemophilus influenzae (including Hib) is a bacterium that can cause a severe infection, occurring mostly in infants and children younger than five years of age. It can cause lifelong disability and be deadly. In spite of its name, Haemophilus influenzae bacteria do not cause influenza (the "flu").
Before Hib vaccination, about 20,000 children younger than five developed severe Hib disease in the United States each year, and about 1,000 died. By 2006, the number of reported Hib cases was down to only 29 for the year. Now, while the majority of fatalities from Hib disease are reported in developing countries where the Hib vaccine is not widely used, fatalities still occur in developed nations when vaccination rates drop.
A conjugate vaccine (made from a tiny fragment of the bacteria's sugar-coat attached to a protein) against Hib was introduced in the UK and Ireland in 1992, and provides long-lasting immunity. Since the introduction of the Hib vaccine, the incidence of meningitis cause by Haemophilus influenzae has been reduced by over 90%, across the UK and Ireland.
The most common symptoms of severe Hib infection are fever and altered central nervous system function. Less common symptoms can be osteomyelitis, septic arthritis, pericarditis, orbital cellulitis, endophthalmitis, urinary tract infection, abscesses, and bacteremia.4
Haemophilus influenzae is widespread in its distribution among the human population. It was first isolated by Pfeiffer during the influenza pandemic of 1890. It was mistakenly thought to be the cause of the disease influenza, and it was named accordingly.
Not long ago H influenzae type b (Hib) was the number one cause of bacterial meningitis. More than half of the cases of Hib infection in the United States involve bacterial meningitis. Thankfully, Hib disease has plummeted by more than 99 percent since the Hib vaccine was introduced in 1988 – in countries where the vaccine is used. Nevertheless, Hib remains a major worldwide problem.
The HIB vaccine is a "conjugate" vaccine. It joins ("conjugates") sugars from the HIB bacteria with a protein from another bacteria. The protein stimulates the baby's immature immune cells so they produce antibodies to the HIB sugars, protecting the child from HIB infection.
Hib infections used to be a serious health problem in the UK, but the routine immunisation against Hib in infants since 1992 means these infections are now rare.
Of the small number of cases that do occur nowadays, most affect adults with long-term (chronic) underlying medical conditions, rather than young children.
Before the Hib vaccine was introduced, about four in every 100 pre-school children carried the Hib organism; after the vaccine was introduced, carriage rates fell below the level of detection.
If you're reading this, it's probably because you heard about Hib and wonder what it is. The good news is, if you live in the United States, you were probably vaccinated against Hib infections when you were a baby.