Meat inspection protocols - Gracey's Meat Hygiene - page 198

either as a random event or as a result of migrant labour
from a country with a high incidence of infection.
The cause of the low but persistent infection in cat-
tle is thought to be due to the access of cattle to water
contaminated with sewage effluents, to the carriage
and dispersal of T. s ag in at a eggs by birds which fre-
quent sewage works or feed on effluent discharge into
rivers or sea and, transport the eggs to pasture and
occasional fouling of pasture by itinerant infected
individuals. In contrast to the developing countries,
cattle of any age are susceptible. When cattle are first
infected as adults, the longevity of the cysticerci is
limited, most being dead within 9 months.
Meat infected with C. bovis is considered to be unfit
for human if generalised, that is, more than one area
or part affected. If the infestation is localised, the parts
not infected may be considered fit following upon
cold treatment - at less than −7°C for at least 3 weeks
or −10°C for at least 2 weeks. Table 9.2 may be used to
assist judgements.
3 Trichinellosis
Trichinella spiralis is a roundworm found in pig, rat,
man and most mammals. The life cycle is indirect.
Adult parasites and infective larvae are unusual in
being present within a single host.
The developing adults (Fig. 9.13) live between the villi
of the small intestine. After fertilisation, the males die,
while females bury deeper into the intestinal mucosa.
After a week, they produce L1 larvae which enter the
bloodstream and make their way to the skeletal muscles.
The larvae penetrate striated muscle cells where they grow
rapidly and begin to coil within the cell. This takes 3-6
weeks after which the larvae are infective. Development
is resumed when the muscle is ingested by another host.
Infection in man is acquired by eating inadequately
cooked pork or its by-products such as sausages, ham and
salami. Smoking, drying or curing meat does not neces-
sarily kill the larvae. Horse meat has increasingly been
implicated in the transmission to man (Fig. 9.12).

has reached its full size of 1.0 cm and is greyish white,
oval and enclosed by the host in a thin fibrous capsule.
The scolex is usually clearly visible. The cysts last from
weeks to years. When they die, they are usually replaced
by a caseous, crumbly mass which may become
calcified. Both living and dead cysts are frequently
present in the same carcase. Humans become infected
by ingesting raw or inadequately cooked meat.
Development to patency takes 2-3 months.
Although C. bovis may occur anywhere in the
striated muscles, the predilection sites are the heart,
the tongue and the masseter and intercostal muscles.
There are two quite distinct epidemiological pat-
terns found in developing countries and developed
countries.
In many parts of Africa, Asia and Latin America,
cattle are reared on an extensive scale, and human sani-
tation is poor. Human infection can be over 20% and
cattle infection 30-60% on routine carcase infection
although the prevalence is thought to be much higher.
In areas such as Europe, North America, Australia
and New Zealand, standards of sanitation are high, and
meat is carefully inspected and generally thoroughly
cooked before consumption. In these countries, the
prevalence of cysticercosis is low, but this may vary with
the diligence of inspection, although one has to weigh
the requirements of detection of cysticercus against the
damage to the carcase and consequent lower value.
Occasionally, a cysticercosis 'storm' can occur when
a high proportion of cattle are infected. This is asso-
ciated with the improper use of human sewage as a
fertiliser or the use of a farm slurry tanker to empty a
human septic tank.
T. s ag in at a eggs may survive for more than 200 days
in sludge. In agricultural practice, the use of human
sludge as a fertiliser should be confined to elevated fields
or to those on which cattle will not be grazed for 2 years.
Other causes of sudden high incidence on a farm
may be due to a tapeworm infection in a stockman

Table 9.2 Guide to judgements on C. bovis findings

Post-mortem finding Judgement

Number Location Status Cyst

More than one Generalised Viable 1 Reject the carcase and the offal

One or more Localised Viable 1 (v) Reject affected organ or carcase part.

Require cold treatment of remainder Caseous or calcified 1 or more (nv)

More than one Generalised Caseous or calcified 1 (nv) Reject the affected organs or carcase parts

Require cold treatment of remainder

nv, non-viable; degeneration has occurred; v, viable.