Biology Reference
In-Depth Information
CLINICAL MANIFESTATIONS
Transmission
In both developing and industrialized countries ETEC infections are transmitted
by contaminated food or water. Both epidemiologic and volunteer studies sug-
gest that the inoculum of ETEC required to establish illness in healthy subjects
is relatively high and that person-to-person transmission is uncommon (
Levine
et al., 1980
;
Roels et al., 1998
). While, 10
8
CFU of ETEC H10407, the strain
used in the majority of volunteer studies, typically leads to moderate to severe
diarrhea in most volunteers (
Porter et al., 2011
), the actual dose required to
establish illness could be several logs lower and the infective dose in developing
countries could be substantially different (
Harro et al., 2011
).
Clinical features
Diarrheal illness caused by ETEC ranges from mild watery diarrhea to severe
life-threatening cholera-like illness in both children and adults (
Sack et al.,
1971
;
Finkelstein et al., 1976
;
Vicente et al., 2005
). Diarrhea caused by ETEC
cannot be distinguished from that caused by
Vibrio cholerae
on clinical grounds
alone (
Sack et al., 1977
). Other symptoms including abdominal cramping are
common, while fever and vomiting occur in roughly 10% or less of cases on
average (
Roels et al., 1998
;
Porter et al., 2011
). Diarrhea caused by ETEC can
be somewhat protracted and last as long as 1 to 2 weeks (
Roels et al., 1998
;
Bolin et al., 2006
). Illness lasting more than 4 days, where vomiting is not a
predominant symptom, should prompt a consideration of ETEC as the offend-
ing pathogen (
Roels et al., 1998
).
Diarrhea caused by ETEC is classically described as watery without the
appearance of gross blood or mucus in the stool. While classically, ETEC infec-
tions have been unceremoniously relegated to causing 'non-inflammatory'
diarrhea, this view may not be entirely accurate. Indeed, symptomatic ETEC
infections elicit sizable fecal lactoferrin responses (
Mercado et al., 2011
), as
well as interleukin-8 that are comparable to those observed with
Salmonella
infections (
Greenberg et al., 2002
). In studies of ETEC in travelers with diar-
rhea, roughly one quarter had fecal leukocytes, and nearly one third were found
to have fecal occult blood (
Bouckenooghe et al., 2000
).
Host susceptibility
Children with A or AB blood group antigens appear to be somewhat more
susceptible to developing symptomatic ETEC infections than those of blood
group O (
Qadri et al., 2007
), suggesting a genetic predisposition to develop-
ment of symptomatic ETEC infections. Likewise, children expressing Lewis
blood group a (Le
a+b-
), thought to be a receptor for CFA/I (
Jansson et al., 2006
),
are more susceptible to diarrhea caused by ETEC expressing CFA/I (
Ahmed
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