Helminthology

Helminths of poultry and ostriches

Author: C NKUNA

Introduction

Worm infections are a common problem in indigenous chickens, free-range commercial layers, breeders, and other types of poultry that have direct contact with their faeces and the intermediate hosts of helminths. Worms are usually not a problem in broilers due to their very short lifespan which is  too short for the worms to complete their life cycles. In addition, end-of-cycle cleanouts of broiler houses also ensure that any worms in the litter are cleaned out.

In a study conducted by Mukaratirwa et al. (2001) on free-range chickens in KwaZulu-Natal, 16 helminth species were found, 12 nematodes and 4 cestodes. This supports previous studies that demonstrated that nematodes were dominant in the free-range birds in Zimbabwe and Ghana. Molla et al. (2012) found that in local backyard chickens on Ethiopia ’s North Gondar –although there were more species of cestodes isolated, the infection burden of the nematodes was higher than that of cestodes (60.38% compared with 54.62%).

Commercially farmed ostriches are generally kept on pasture for very long periods since they are grazers. They are therefore exposed to both nematodes and cestodes. Worm infestation can severely affect health and viability –especially of young ostriches.

Nematodes

Nematodes are the commonest and most important helminth group in poultry. More than 50 species have been described in poultry. Of these, most cause pathological damage to the host. The nematodes of poultry –unlike those of mammalian livestock –often have intermediate hosts, which is probably an adaptation to their foraging lifestyle and omnivorous feeding habits.

Crop and oesophagus

Capillary or Threadworms

Capillaria species

The Capillaria spp. are small roundworms and are found in many mammals –but are most important in poultry. Various Capillaria species are found in different organs in the birds. Species of importance in poultry are: C. annulata, C. anatis, C. obsignata, C. caudinflata, C. aerophilia and C. contorta. C. annulata and C. contorta are found in the crop and oesophagus.

Morphology

Capillaria species are very small and hairlike worms that are very difficult to see in the stomach contents. Size ranges from as small as 6 mm through to 80 mm. C. annulata females are the largest at 37- 80 mm long, with the males being 15-25 mm long. The eggs have bipolar plugs and measure 60 x 25 μm. C. contorta males are the same length as C. annulata males, while the females are shorter –measuring only 27-38 mm. The C. contorta eggs are equal in size to the C. annulata eggs –at 60 x 25 μm.

Life cycle

C. annulata and C. contorta have indirect life cycles –with earthworms being the intermediate hosts. Unembryonated eggs are shed in the faeces and are ingested by the earthworms, where they develop into the first larval stage in 9 to 14 days. The host then ingests the earthworm and becomes infected. C. contorta can also have a direct life cycle, with the L1 embryonated eggs as the infective stage. This means that poultry kept in houses –away from the intermediate host –can still be infected.

Clinical signs and pathogenicity

Capillaria spp. can be highly pathogenic for birds kept in deep-litter and freerange systems –both commercial and indigenous –where a build-up of infective eggs in litter or soil can occur. Young birds are more susceptible than older birds. Adult worms burrow into the anterior end of the oesophageal mucosa –causing inflammation. Heavy burdens can result in inflammation and thickening of the oesophageal and crop mucosal walls, which can cause death. C. contorta infections can result in severe anaemia, which can be fatal. Less severe burdens can cause loss of weight and condition, which in turn leads to a loss of production.

Zigzag worm

Gongylonema ingluvicola

G. ingluvicola is a roundworm with a predilection for the crop, oesophagus, and rarely the proventriculus, of chickens, turkeys, pheasants and quails.

Morphology

The female worm is 32-55 mm long and the males are 17-20 mm long. The eggs are approximately 35 x 58 μm. The anterior part of the body has numerous characteristic round or oval thickenings –called cuticular plaques –on the cuticle.

Life cycle

The life cycle is indirect and includes the beetle Copris minutus and the cockroach Blatella germanica as intermediate hosts. The eggs are shed in the faeces and are eaten by beetles and cockroaches. The worm develops in the intermediate host into infective larvae over 30 days. Birds become infected after eating the intermediate hosts that contain the infective larvae L3.

Clinical signs and pathogenicity

Adult parasites may cause inflammation and hypertrophy –with cornification of the epithelium in chronic infections. The pathogenicity is dependent on the burden of infection.

Proventriculus and gizzard

Tetrameres species

T. americana and T. fissispina are found in various bird species in Africa. The adult worms are found in the proventriculus –detriculus and the walls of the gizzard.

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Clinical signs and pathogenicity

Infected birds may be emaciated and sluggish or weak. The worm infection weakens the immunity of the birds –making then susceptible to other infections. Adult D. nasuta attach to the wall of the proventriculus, causing ulcerations at the attachment sites. When the worm burdens are high, a proliferative proventriculitis with necrosis and sloughing of the mucosa is evident...

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