A worldwide push to treat a leading cause
of blindness may backfire in the long run,
because it appears to leave people more vulnerable
to re-infection, a new study reports.
Trachoma is the second biggest cause of blindness
worldwide. In the developing world, one million
people are blind from it, while 10 million
more will go blind without surgery.
Hopes were raised that it could be eradicated
by giving children one dose of an antibiotic,
once or twice per year, to stop the infection
that causes it. However, the new study shows
that although children who get the antibiotic
pill recover, they are four times more likely
to become re-infected.
Trachoma is caused by Chlamydia bacteria,
carried to people’s eyes by flies that have
also visited open latrines. The infection
causes inflammation, eventually becoming so
severe that the eyelid becomes deformed, forcing
the eyelashes to turn inwards and stick on
to the eyeball.
This causes debilitating pain and can only
be corrected by surgery. Practice has shown
that treating the infection with antibiotic
ointment fails to improve the situation long-term,
since most sufferers fail to apply their medication
for the six weeks necessary to completely
eradicate infection.
Combined approach
In 1999, research showed that one dose of
the antibiotic azithromycin, given once or
twice per year to the children most at risk,
could cut rates of inflammation. This year,
Pfizer, the company that makes the drug, promised
to donate unlimited quantities to countries
carrying out a World Health Organization plan
to combine surgery and antibiotics with better
hygiene. The WHO hopes to eliminate trachoma-caused
blindness by 2020.
However, a new study has found that azithromycin
has an unexpected effect. Berna Atik at Children’s
Hospital Oakland Research Institute in California,
US, and colleagues measured infection rates
for three years in three villages in Vietnam,
where as many as 17% of children in rural
villages are infected.
In two of the villages, azithromycin pills
were given to all school-age children who
had trachoma infections, and their households.
All these children were then given a further
dose of azithromycin a year later. In the
third village no one got azithromycin, although
all obvious infections were treated with a
different antibiotic ointment applied to the
eye.
Sexually-transmitted disease
To their surprise, the researchers found
that the number of new cases increased over
the three-year-period in the villages that
received the azithromycin. Worse still, re-infections
shot up fourfold compared to the ointment-only
village, but only in villages treated with
azithromycin.
Atik thinks treating the infection with azithromycin
shortened the time the immune system was exposed
to the bacteria, and so reduced the immune
response to new infections later. Interestingly,
previous research in Canada showed a similar
resurgence in re-infection when sexually-transmitted
Chlamydia infections were treated with
azithromycin.
Rather than eradicating the debilitating
disease, widespread treatment using this antibiotic
may increase the re-infection rate and make
the overall rate of infection even worse,
the researchers say. Efforts to develop a
vaccine to the bacteria were abandoned in
the 1960s, but in the long run, a vaccine
might be the only thing that will finally
end the misery of trachoma, they add.
Journal reference: Journal of the American
Medical Association (vol 296, p 1488)
