Introduction to Human Nutrition

Food Safety 339

to cattle within weeks to months of its onset. The
incubation period is between 2 and 10 years. Affected
animals may display changes in temperament, such as
nervousness or aggression, abnormal posture, lack of
coordination, and diffi culty in standing, decreased
milk production, or loss of body weight despite con-
tinued appetite. Most cattle with BSE show a gradual
development of symptoms over a period of several
weeks or even months, although some can deteriorate
very rapidly. While the original source of the agent
responsible for BSE remains unknown, currently
the most plausible explanation is that a novel TSE
appeared in the UK cattle population in the 1970s and
subsequently spread through contaminated meat and
bone meal fed to cattle. The International Offi ce for
Epizootic Diseases (OIE) reports cases on its website
(www.oie.int).

Creutzfeldt–Jakob disease and new
variant CJD

CJD is a fatal disease of humans, fi rst described in the
1920s and found worldwide. CJD is predominantly a
sporadic disease, but about 14% of cases are familial

(inherited) and associated with genetic mutations.

Less than 1% are iatrogenic (i.e., accidentally trans-

mitted from person to person as a result of medical

or surgical procedures). Classically, sporadic CJD

occurs in those over 65 years of age and presents as a

rapidly progressive dementia with myoclonus (shock-

like contractions of isolated muscles), usually fatal

within 6 months. Surveillance of CJD, a human neu-

rological disease, was reinstituted in the UK in 1990

to evaluate any changes in the pattern of the disease

that might be attributable to BSE. The overall inci-

dence of CJD rose in the UK in the 1990s, although a

portion of this increase was due to improved ascer-

tainment of CJD in older people as a result of the

reinstitution of surveillance.

New variant CJD, also referred to as variant CJD

(vCJD), is a newly recognized disease in humans,

which was fi rst diagnosed in the UK in the mid-1990s.

In contrast to the traditional forms of CJD, vCJD has

affected younger patients (average age 29 years) and

has a longer duration of illness (approximately 14

months). Early in the illness, patients usually experi-

ence behavioral changes, which most commonly take

Table 14.5 Food-borne protozoa

Occurrence Transmission Defi nitive host Incubation Infective dose Pathogenesis

Giardia intestinalis
worldwide

Food-borne, water-

borne, person–

person

Humans,

domestic, and

wild animals

3–25 days Low (~10 cysts) Chronic diarrhea, malabsorption,

weight loss

Entamoeba
histolytica
worldwide

Food-borne, water-

borne, person–

person (food

handlers)

Humans 2–4 weeks Very low

(~1 cyst)

Amebiasis, abdominal pain,

fever, diarrhea, ulceration of

the colon (severe cases)

Toxoplasma
gondii
worldwide

Food-borne (raw or

inadequately

cooked infected

meat), water-

borne, fecal–oral

(infected cats)

Humans, cats,

several

mammals

5–23 days ~1–30 cysts Mostly asymptomatic. In severe
cases: hepatitis, pneumonia,
blindness, severe neurological
disorders.
Can also be transmitted
transplacentally resulting in a
spontaneous abortion, a
stillborn, or mental/physical
retardation
Cyclospora
cayetanensis
worldwide

Food-borne,

water-borne

Humans Several days

to weeks

Not known,

probably very

low

Often asymptomatic.
Abdominal cramps, vomiting,
weight loss, diarrhea
Cryptosporidium
parvum
worldwide

Food-borne, water-

borne, animal–

person, fecal–oral

Humans,

domestic, and

wild animals

Diffi cult to

defi ne, in

most cases

3–7 days,

occasionally

longer

Very low (~1

cyst)

Often asymptomatic.

Abdominal cramps, vomiting,

weight loss, diarrhea