Dear Schisto members!
Several months ago, after Wilfried Haas sent a message about schisto-
infections, Christopher Bayne sent out a general query asking for news about
either laboratory infections or field infections among schisto research workers.
He has now collected the responses, and has sent a summary which is forwarded
below. If you want to reply to this message, please send your e-mail to the
Forwarded message of Christopher Bayne:
Some time ago, Newsgroup members received word from Wilfried Haas about
accidental infections with schisto. An excerpt from his message follows:
"Therefore, schisto-workers, think about a possible schistosomiasis, when
you need considerably more willpower to rise from your bed in the
morning than usual, when you need willpower to mobilize your strenth to
go up the stairs, or also when you have extraordinary problems to follow
lectures! However, be prepared, that you have to perform many
schisto-diagnoses with negative results, after descibing these symptoms
to your coworkers!"
Nine people responded to my query, though two of these merely asked how I
expected to determine relative frequencies of infections if I learned only
about positive data. In fact almost all who responded also mentioned how
many people were involved and how many years they have worked with
schistosomes. Here (with names with-held) are the results:
1. Three or four people over 10 years regularly handling cercariae - no
2. Sixty or more people over 27 years handling fercariae - no known
3. Forty or more people over 25 years - no known infections.
4. One person became infected during field work in Tanzania, and treats
himself regularly after potential exposures.
5. Several people over 20 years in a lab in which millions of cercariae are
handled weekly; 2 technicians became seropositive in this time. There were
no other symptoms. The individuals were treated with Praziquantel.
Infections were thought to be due to torn gloves.
6. One response (no lab infections) mentioned only that divers in Lake
Malawi are being infected increasingly often, coinciding with harvesting of
snail-eating fish. Implication: leave natural agents of biological control
7. I attach an excerpt (slightly edited) from the remaining response.
Considered along with Haas' original one, it should make us all think!
"...although we have never had accidental infection in the two labs in
which I have worked on schisto for the last 20 years, we have found 2
graduate students and 2 post-doc workers to have (or probably have in one
case) naturally acquired schisto infections. The two students were both
from schisto endemic countries, one Egyptian and the other East Africian.
Both had been absent from endemic areas for at least 6 months before being
diagnosed. One had been feeling generally unwell, with abdominal pain and
tiredness for some time, and asked to be examined for eggs. We found S.
haematobium (not kept in the lab). This made the second student consider that
he had the same general feeling of lethargy and weakness since before he
arrived in England (maybe for over 18 months). We found that he had S.
mansoni eggs in his faeces. Both reported a rapid improvement after
Both post-doc workers were presumed infected on holiday, one in Tunisia and
the other in Mali (both had been swimming in natural water bodies). One
felt unwell for the 6 months since her return from holiday and requested
diagnosis (S. haem. eggs found), and other had also suffered weakness,
particularly in the mornings, tireness and general abdominal discomfort.
When she donated blood to the lab for the isolation of eosinophils, it was
found that her eosinophil count had increased 10-fold from the previous
times that she had donated blood before her holiday. We failed to find
schisto. eggs in her faeces or urine, and the Hospital for Tropical
Diseases in London also failed to detect eggs. However, in the absence of
any other detectable infection or physiological problems, she was drug
treated for suspected schistosomiasis. Her eosinophilia disappeared within
4 weeks and she also recovered her full strength within this time.
The common feature of all these cases was the general feeling of weakness
and lethargy (particularly in the mornings), with some abdominal
discomfort, usually discribed as a general vague discomfort, but some
moderately severe pain in one or two of the individuals. Even though the
people infected could be considered 'experts' on schisto, and at least
three of them realised that they had been potentially exposed to schisto,
they had felt unwell for between 3 and 18 months before considering the
possibility that they had schistosomiasis. The egg counts in all cases were
Clearly the symptoms of low grade schistosomiasis do not remind biologists
working of the subject of the symtoms they generally read about in the text
books. I don't know if Medic's are more aware of these symtoms."
THANK YOU for responding to the query. This ends my involvement with
distributing information on schisto infections.
Christopher J. Bayne, Ph.D.,
Professor of Zoology, Oregon State University,
Corvallis, Oregon 97331-2914, USA
e-mail: baynec at bcc.orst.edu