FEARS that polio vaccination might be stopped too soon have been heightened
by the discovery of suspected wild-type polio in sewage in the French city of
Strasbourg.
Doctors are combing medical records to see if misdiagnosed patients could
have been affected by the virus. However, suspicion has centred on activities in
Strasbourg鈥檚 many biomedical laboratories.
The discovery was made when officials investigated a city water pipe last
May, after it was contaminated by sewage. Sixty cases of gastroenteritis in the
area served by the water pipe confirmed the sewage contamination.
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To their surprise, the authorities also found polio. 鈥淏ut we thought it was a
vaccine strain,鈥� says Alain Guillard, a sanitary engineer for the city. Live,
weakened polio virus is used in oral polio vaccine, and occurs in a fifth of
sewage samples analysed in Paris, he says. To make sure, samples were sent to
the World Health Organization鈥檚 reference laboratory for enteroviruses at Claude
Bernard University in Lyon.
鈥淲e were very surprised to discover that it was a Mahoney-type strain,鈥� says
Jean-Jacques Chomel, head of the lab. This strain killed thousands every year
before vaccination began in the 1950s. Wild Mahoney virus is considered extinct
in France.
It could be a strain that was preserved in a laboratory, says Chomel. To find
out, his team is sequencing the critical genes of the Strasbourg strain.
The WHO wants to stop universal polio vaccination once it has declared polio
eradicated鈥攊t hopes this will be in 2005. But Chomel says that the
Strasbourg incident highlights the continuing risks posed by the virus, whether
or not it is an escapee. 鈥淓ither way, this finding shows it would be stupid to
stop polio vaccination any time soon.鈥� Current worries centre on the
persistence, and possible reversion to pathogenic forms, of vaccine strains of
polio virus in the environment
(New 杏吧原创, 5 February 2000, p 20).
Some of Strasbourg鈥檚 citizens must have swallowed the virus. The four-month
incubation period for poliomyelitis has now elapsed, and no cases of paralysis
have been recorded since the incident. But the incident happened during an
outbreak of viral meningitis, and polio can cause meningitis. Unlike most French
cities, says Chomel, Strasbourg sent no meningitis samples to Lyon for analysis.
So some of these cases could have been polio.
Polio virus can be excreted by human carriers, says Tjeerd Kimman of the
National Institute of Public Health and the Environment near Utrecht in the
Netherlands. 鈥淏ut we estimate that five per cent of a population must be
infected before you can find the virus in sewage,鈥� he says. Such a large number
of carriers of a lethal polio virus in Strasbourg would be unlikely without
cases of paralysis. So it seems more likely that a concentrated dose escaped
from a laboratory.
Jean-Fran莽ois Donnard, a public health official in Strasbourg says:
鈥淲e are questioning 40 laboratories in the area to see if they used such a virus
in the past 10 years.鈥�