Biology Reference
In-Depth Information
TABLE 7.1
Shigella
virulence-associated loci encoded on the virulence
plasmid—cont'd
Locus
Protein/activity
Role in virulence
ipgC
IpaB and IpaC
ipgA
IcsA
ipgE
IpgD
spa15
IpaA, IpgB1, OspC3
Structural elements of T3SS
mxi/spa
∼
20 proteins
Regulatory factors
virF
Transcriptional
activator
Temperature regulation of virB
virB
Transcriptional
activator
Temperature regulation of
ipa
,
mxi
, and
spa
virulence operons
164 million (with 1.1 million deaths), the vast majority of cases occurring in
developing countries (
Kotloff et al., 1999
). Over-crowding, poor sanitation,
substandard hygiene and unsafe water supplies are conditions that contribute to
outbreaks of shigellosis in these areas. The greatest frequency of illness due to
Shigella
occurs among children less than 6 years of age (
Kotloff et al., 1999
).
In the US, outbreaks of shigellosis and other diarrheal diseases are increas-
ing in day care centers as more single-parent and two parent working fami-
lies turn to these facilities to care for their children (
Levine and Levine, 1994
;
Arvelo et al., 2009
). Inadequate personal hygiene habits coupled with typical
toddler behavior such as oral exploration of the environment create conditions
ideally suited to transmission of bacterial, protozoan, and viral pathogens that
are spread by fecal contamination. Transmission of
Shigella
in this population
is very efficient and the low infectious dose for causing disease increases the
risk for shigellosis. Family contacts of day care attendees are also at increased
risk. Shigellosis can be endemic in other institutional settings as well. Pris-
ons, mental hospitals, and nursing homes, where crowding and/or insufficient
hygienic conditions may exist, can provide an environment for direct fecal-oral
contamination.
When natural or man-made disasters destroy a region's sanitary waste treat-
ment and water purification infrastructure, developed countries take on the con-
ditions of a developing country. These conditions place a population at risk for
diarrheal diseases such as cholera and dysentery. Examples include famine and
political upheaval in Somalia and the war in Bosnia (
Levine and Levine, 1994
).
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