This parasite has two names: the cyst stage, Cysticercus bovis was named before it was known to be connected to the life cycle of the beef tapeworm of man, Taenia saginata.
Beef measles are small blister-like cysts 5-10 mm in diameter that occur most commonly in cardiac, jaw, tongue, diaphragm musculature and less commonly in all striated muscles throughout the body of cattle. Infected muscle has the appearance of measles.
Figure 1. The eggs of Taenia spp and Echinococcus spp look the same. Image courtesy of the National Centre for Veterinary Parasitology, ncvetp.org
The economic importance of this parasite is that visible cysts cause downgrading of expensive commercial cuts of meat during meat inspection. Affected carcases are condemned.
Adult tapeworms in people can grow to between four and 10 metres in length and can live for up to 25 years. This tapeworm has up to 2,000 segments and each segment can contain up to 80,000 eggs.
The beef tapeworm of man is a human parasitic disease.
Usually there are no symptoms.
Infection results from consuming the measles or cysts in raw or inadequately cooked beef. The tapeworm is not transmitted from person to person.
Beef measles infections of cattle are now uncommon in this country. However, disease storms do occur as a result of sudden exposure of immunologically naïve cattle to the eggs of T. saginata when, for example, raw sewage passes onto pasture due to a malfunction of an on-farm septic tank, or at a sewage treatment facility.
Large numbers of animals often in a small geographical area become infected at the same time. Tapeworm eggs are extremely resistant to environmental conditions and can remain viable for two to four months on pasture.
It is increasingly possible that infection cycles are being perpetuated in semi-rural areas close to major cities where young cattle grazed on contaminated pastures are being slaughtered on-farm to produce meat for human consumption.
Figure 2. Beef measles caused by Cysticercus bovis in the heart of a cow. Image courtesy of the National Centre for Veterinary Parasitology, ncvetp.org
Adult tapeworms live in the small intestine of man. The intermediate stages in cattle are found in striated muscles, heart, tongue, masseter muscles and diaphragm.
The human health impacts of infection with the tapeworm are usually minimal. The impact on cattle is also minimal.
This is an indirect predator / prey life cycle where a larval stage occurs in cattle. The definitive (predator) host is man and the intermediate (prey) hosts for the cysts are cattle.
The tapeworm occurs in the small intestine of man. Segments (proglottids) are very active and up to nine can be shed a day, or single ones can leave the host spontaneously by migrating out through the anus. Outside the host, segments can crawl a considerable distance from the faeces disseminating eggs in the process.
Cattle become infected from eggs dispersed from human faeces deposited indiscriminately around cattle yards. In the small intestine the embryos are released and enter the blood stream, move throughout the body and settle in skeletal and cardiac muscles. Full development of the cyst takes 16-18 weeks. Viable cysts can survive up to 30 months after infection but more commonly, cysts calcify, becoming hard and non-viable.
Beef measles cysts are confirmed during meat inspection procedures by examination of the predilection sites such as heart, masseter muscles, tongue and diaphragm, but detection of the many small cysts buried throughout other striated muscles may be low.
Treatment for humans consists of administration of a single dose of niclosamide or praziquantel. Cattle do not require treatment.
Prevention is needed to break the life cycle by reducing cattle pick up of tapeworm eggs deposited indiscriminately on pastures around cattle pens, and preventing human ingestion of infective cysts by only eating beef that has undergone meat inspection and ensuring that it is well cooked.