The Condition

Cestodes

A vast number of poultry tapeworms or cestodes have been identified, with a wide range of intermediate hosts. These are not considered of great pathogenicity, especially in modern poultry production systems.

All tapeworms of poultry have indirect life cycles with intermediate hosts such as earthworms, beetles, flies, ants or grasshoppers. The intermediate hosts are essential to perpetuate the life cycle and infections are therefore rare in indoor systems (Permin and Hansen, undated). As with other helminths, organic and other free-range systems are at a particular risk from infestation.

The cestodes are flattened, ribbon-shaped worms, usually segmented. Cestodes use arthropods and other invertebrates as their intermediate hosts. Poultry become infected by swallowing infected snails, slugs or insects. In turn, the invertebrate hosts become infected by ingesting the eggs or egg-bearing segments of the worm, along with their food. Following ingestion by the intermediate host, the eggs hatch in the intestinal wall and enter the body cavity. After a few days they become transformed into small, white cysts (cystercercoids). These cysts are visible to the naked eye when removed from the host. Microscopic examination will show the head of the tapeworm near the centre of the cyst.

The cysts take approximately three weeks after the initial ingestion to develop into this embryonic form. No further development occurs in the intermediate host, although the cysticercoids may remain alive for much longer than this. The host may remain infective to birds for many months.

When the invertebrate host is ingested by poultry, the cysticercoid is freed from the body of the host by the action of digestive juices. The tapeworm head then becomes attached to the intestinal wall. New segments begin to form and within 3 weeks of ingestion of the host a mature tapeworm has developed. Therefore, the entire life-cycle can take 6 weeks for completion, although this may be longer under unfavourable conditions.

One of the most common tapeworms affecting poultry systems is Davainea proglottina. The mature worm is approximately 4mm in length and consists of 4-9 segments. The intermediate hosts for this worm are the molluscs or snails. Tapeworm segments passed in poultry faeces are ingested by snails (of the genera Agriolimax, Arion, Cepea and Limax) and within 3 weeks a cysticercoid is produced. Adult tapeworms are produced in an infected chicken 8-15 days after ingestion of an infected snail.

Affected birds lose weight, start to breathe rapidly and their feathers become ruffled and dry. At post-mortem, tapeworms can be seen in the duodenum and there is a thickening of the intestinal mucosa.

The most pathogenic of poultry tapeworms is Raillietina cesticullus, which has the beetle as its host. The mature tapeworm may be 12-13 cm in length. Birds become infected after feeding on infected beetles which will in turn have become infected from poultry droppings. Heavy infestations can cause severe weight loss (Ackert and Case, 1938). Chickens over 10 weeks tend to be less susceptible than younger chicks (Ackert and Reid, 1937).

Trematodes

Trematodes are leaf-like parasitic organisms that are invariably associated with snails and wet environments. They are less pathogenic than roundworms, and very large numbers can be found in apparently healthy wild birds. Trematode infections are most commonly associated with wild-fowl and domestic ducks and geese. The trematodes are particularly prevalent in water-fowl as the intermediate hosts are molluscs.

The table below describes some of the more common poultry tapeworms and trematodes affecting poultry.

Species

Principal host

Intermediate host

Length of mature worm (mm)

Amoebotaenia cuneata

Chicken

Earthworms

3

Choanotaenia infundibulum

Chicken

Housefly, beetles

50-200

Davainea proglottina

Chicken

Slugs, snails

4

Echinostoma revolutum

Chicken, duck, turkey

Various species of water snail

10-22

Hymenolepsis cantaniana

Chicken

Beetles

20

Hymenolepsis carioca

Chicken

Stable fly, dung beetles

40

Prosthogonimus macrorchis

Chicken, duck

Water snail and then dragon fly

5-7

Raillietina cesticullus

Chicken

Beetles

50-150

Raillietina tetragona

Chicken

Ants

100-250

Raillietina magninumida

Chicken

Ants

200-340

Raillietina echinobothrida

Guinea-fowl

Beetles

50-150

From Jordan and Pattison (1996)

For more on life-cycle and epidemiology of poultry tapeworms see FAO Handbook The Epidemiology, Diagnosis and Control of Poultry Parasites (Permin and Hansen, undated)