Biology of Disease

cause caries by forming plaque on the tooth enamel, where they catabolize
sugars to produce acid that demineralizes enamel and allows the dentine
to be eroded. Abscesses of the roots of teeth can also be caused by mixed
bacterial infections.

Periodontal (gum) diseases are inflammatory conditions that attack the
gums, bone, and other supporting structures of the teeth. The extent of the
inflammatory response depends upon the types of pathogens involved and
the effectiveness of the immune response. However, they are major causes of
tooth loss in adults. Gingivitis is the earliest form of periodontal disease and
occurs when plaque accumulates on the teeth near the gums, which become
inflamed and bleed easily. If detected and treated early, gingival tissues will
return to normal without long-lasting damage. Untreated gingivitis progresses
to periodontitis, which is also known as pyorrhea. Plaque hardens and extends
from the gum line to the tooth root causing the gums to detach from the
teeth and form pockets. Periodontal pockets create room for greater bacterial
activity, particularly of facultative and obligate anaerobic bacteria leading to
a progressive cycle of tissue damage until eventually the bone supporting the
teeth is destroyed resulting in their loss.

Stomach and intestinal infections are caused by viruses, bacteria, protozoa and
worms, all of which may be transmitted in food, contaminated drinking water
or by fecal–oral contact. The need for strict personal hygiene is emphasized
because these are the most frequent infections of children under five years
of age. Approximately 40% of cases of diarrhea (Chapter 11) in children are
caused by rotaviruses (Figure 3.12). In the very young this is potentially lethal
and the WHO has estimated that out of the nearly two billion annual diarrhea
diseases worldwide, three million end fatally.

Figure 3.13 indicates a number of pathogens that can infect the GIT. The
acidic environment and proteolytic enzymes of the stomach kill most

INFECTIONS OF THE GASTROINTESTINAL TRACT

CZhhVg6]bZY!BVjgZZc9Vlhdc!8]g^hHb^i]:YLddY ),

Figure 3.10 Electron micrograph of Candida

albicans.Courtesy of H. Cotterill, Manchester Royal

Infirmary, UK.

Figure 3.11 Electron micrograph of Streptococcus

mutans.Courtesy of Professor J. Verran, School of

Biology, Chemistry and Health Science, Manchester

Metropolitan University, UK.

Figure 3.12Electron micrograph of rotavirus.

Courtesy of H. Cotterill, Manchester Royal Infirmary, UK.

Esophagus

Stomach

Duodenum

Jejunum

Ileum

with

Peyer's

patches

Colon

Helicobacter pylori

Rotaviruses,

Escherichia coli (ETEC, EPEC),

Vibrio cholerae,

Giardia lamblia

Campylobacter species,

Salmonella enterica,

Yersinia species

Clostridium difficile,

Escherichia coli (EIEC, EHEC),

Shigella species,

Entamoeba histolytica

Rectum

Anus

Figure 3.13Some infectious organisms associated with the gastrointestinal tract. See text for
discussions.