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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