Pertussis, more commonly known as whooping
cough, has unfortunately shown a strong resurgence within the past few years
not only in the United States, but in countries across the globe as well. In fact, there were a reported 27, 550 cases
of pertussis in the United States in 2010, marking the year as that with the
most numerous cases of the infection since 1959. This new-found prominence in the disease has in
turn resulted in a variety of public service announcements, on the radio and
television, warning the general public of the symptoms and the importance of
vaccination, especially for those with infants, as they tend to be the group most
susceptible to the infection. Without a
doubt, the most resonating part of the segments are the sound bites of infants
first going into coughing fits before beginning to gasp for air, the
characteristic whooping sound, placed intermittently throughout the duration of
the message. If the information in the
public service announcement does not catch your attention, the pained sounds of
sick infants definitely will.
Pertussis is a highly contagious respiratory disease caused by an
infection by the bacteria Bordetella
pertussis. The bacteria attack the
upper respiratory system, releasing toxins that cause inflammation. This in turn causes those infected to descend
into bursts of rapid coughs which are then followed by a period of attempting
to draw in as much air as possible in order to recover from the depletion in
oxygen levels in the body due to the long coughing spells. The disease often leads to the development of
pneumonia, and in the worst cases the depletion in oxygen levels can lead to
brain damage and even death. For this reason,
physicians highly recommend vaccination to those in direct contact with infants
as it has shown to significantly decrease the chance of spreading the disease.
Despite the effectiveness of vaccination, public health studies have
shown that pertussis has again begun to reemerge, but unexpectedly in countries
with highly vaccinated populations.
Though factors such as decreases in vaccine coverage and vaccine quality
could play a role in this resurgence of the disease, researchers in the
Netherlands hypothesize that the bacteria has evolved to resist the effects of
vaccines.
To test this theory, the researchers collected bacteria strains from
1949 to 1996, grouping them into periods of 5 to 8 years, and determined the frequency
of different DNA fingerprint types within each of said periods. The results showed a distinct difference
between in the fingerprints types found before and after usage of the vaccine
became widespread. Moreover, the results
showed that genotypic diversity drastically decreased soon after implementation
of the vaccine, suggesting that only those bacteria with the correct genetic coding
were able to resist being wiped out.
However, over the years the genotypic diversity has increased, implying that
those surviving strains have continued to adapt and mutate so as to remain
unaffected by vaccines.
In addition, the researcher also investigated the effects of the polymorphism
observed in pertussis toxin and pertactin, two important virulence factors
necessary for the bacteria to be able to bind to the host’s cells. Results showed the polymorphisms were non-conservative
for the most part, which would imply that Darwinian selection plays an important
role in this adaption found in the bacterial DNA. Specifically, results showed that tandem
repeats in the coding existed near the RGD amino acid motif, making the area
quite susceptible to mutation as a result of slipped-strand mispairing during
DNA replication. Said mutations affect
areas of the bacteria related to binding with T-cells, causing those bacteria
with sequences most distinct from those found in the pre-vaccination era
selected to be selected. Because of the
mutations, the receptor binding area has changed such that the host’s T-cells
can no longer bind to the bacteria, meaning that the bacteria no longer has to
fear being eliminated from the host.
Though the usage of vaccines to help fight the spread of pertussis has
without a doubt been quite beneficial at reducing the number of pertussis-related
deaths over the decades, it would seem that yet again the bacteria are adapting
and evolving to resist the effects of said vaccines. Those bacteria able to survive the initial wave
of vaccines have evolved and given way to new mutants that are beginning to
show resistance against T-cells. Though
this is most likely not the only reason why pertussis has shown an increase in
activity within the past few years, it does open up more doors towards the
continued effort to eventually bring immunity towards the disease hopefully sometime
in the future.
Danielle Spencer
Word Count: 760
References:
1. http://www.cdc.gov/pertussis/
2. Mooi, Frits R., Inge H. M. van Loo, Audrey J.
King. Adaptation of Bordetella pertussis
to Vaccination: A Cause for Its Reemergence? Emerging Infectious Diseases.
7(3, Supplement): 526-528, 2001.
Image from: http://medblog.medlink-uk.net/gangnamlad/files/2013/02/whooping-cough.jpg
I wonder why pertussis hasn't been completely eradicated like polio. Could it be because polio vaccination was mandatory? In the case of pertussis, it's voluntary, so some strains managed to survive the initial wave of vaccination and mutated to adapt to the new environment.
ReplyDeleteI think it is important to note that a new pertussis strain may have evolved to avoid the attacks of an immune system primed through vaccination to eliminate the old strain. A new vaccine can certainly be developed to train the immune system against the new strain of virus. Therefore this potential mutation is very similar to bacterial antibiotic resistance with the caveat that a new vaccine may be easier to produce and is much more disease specific than a new antibiotic.
ReplyDeleteAlso notable is that sometimes when a disease does decrease so much in the population, as pertussis did after the initial vaccinations, then people no longer feel the need to be immunized. They don't see anyone around them getting sick from this disease and therefore do not feel a direct threat of illness. I don't know if there is any data showing a decrease in vaccination rates or simply that the evolution of the bacteria caused the new spikes in pertussis.
ReplyDeleteAre there any plans to develop new pertussis vaccines targeting resistant strains of bacteria?
This is another great example of how our medical technology has been a wonderful factor in human survival, but has prevented our populations from directly evolving with the bacteria. As a result, we need to evolve our technologies, rather than ourselves, to keep up. Thankfully, this appears to be a bit easier!
ReplyDeleteI think this blog is interesting as I did a topic similar to this one! It makes you really think about the cost of medical vaccines when it comes to viruses because their rapid rate of development contributes to their ability to evolve so quickly.
ReplyDelete