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A number of parasitic nematodes are found in poultry. A brief description of some of the more prevalent African species is given below, summarised from Permin and Hansen (1998) and Yazwinski and Tucker (2008).

1.11.1 Ascaridia galli

These are large, (Males 50-76mm, Females 60-116mm) thick, yellowish-white worms, primarily found in the small intestine, but occasionally reported from crop, gizzard, body cavity, oviduct and egg. This species has a direct life cycle; eggs become infective after 7-28 days and can survive low environmental temperatures, with larvae maturing after 28-30 days. Pathogenic effects include retarded growth, anaemia, hypoglycaemia, increased

mortality and infection can increase the effects of coccidiosis. Birds develop an age-related resistance, and arrested larval development often occurs in birds over 3 months. Birds’ nutritional status can also affect resistance, particularly levels of Vitamins A and B, calcium and lysine.

1.11.2 Heterakis gallinarum

A small (Males 7-13mm, Females 10-15mm) white worm found in the caeca of chickens, turkeys, game birds and waterfowl. It has a direct life cycle, although eggs ingested by earthworms are still infective. The eggs are indistinguishable from those of A. galli. Larvae live in the walls of the caeca for 12 days then become free in the lumen. The pathogenic effects include caecal inflammation, and nodule formation and secondary infections, with hepatic granulomata occasionally reported. H. gallinarum is a vector for the protozoan

Histomonas meleagridis (Blackhead), which is a particular problem for turkeys. 1.11.4 Subulura (Allodapa) brumpti

These are small (Males 7-10mm, Females 9-14mm) worms with curved tails, found in the lumen of the caecum. Their intermediate hosts are beetles or cockroaches. There are no known pathogenic effects.

1.11.3 Capillaria spp.

There are many species of this nematode which infect the chicken. The size varies depending on species, with most being 10-25mm but some species reaching 60mm long. Species can be divided into those found in the crop or oesophagus (C. annulata, C. contorta); those found in the small intestines (C. caudinflata, C. obsignata, C. bursata) and those found in the caecum (C. anatis). Life cycles are either direct or involving an earthworm intermediate host, depending on species. All species are pathogenic, causing inflammation and ulceration of tissues. All ages of bird may be affected. Weight loss,

Chapter 1 | General introduction and thesis objectives weakness and poor growth are the predominant signs, but heavy burdens, especially of the crop worms, may cause significant mortality in young birds.

1.11.5 Cheilospirura (Acuaria) hamulosa

These are medium (Males 9-19mm, Females 16-25mm) worms found in the gizzard lining, where they cause small lesions and nodules in the gizzard endothelium and musculature. However, they have little pathogenic effect except in heavy infestations. Intermediate hosts include grasshoppers, weevils and beetles.

1.11.6 Dyspharynx spiralis

Small (Males 7-8mm, Females 9-10mm) worm rolled in a spiral, found in the proventriculus with their heads buried in the mucosa. Intermediate hosts are isopod spp. such as the woodlouse. Pathologies caused by these worms involve ulceration, inflammation and pronounced thickening of the proventriculus, with signs of weight loss and anaemia, and potentially heavy losses of young birds.

1.11.7 Epidemiology

The proportion of birds under village conditions positive for nematode infections in previous studies in Ethiopia has been reported to be around 75%. The most common species reported are A. galli (32-55%), H. gallinarum (17-48%) and S. Brumpti (17-27%). Other species have been reported at rates of less than 5% (Eshetu et al., 2001; Ashenafi and Eshetu, 2004a; Tolossa et al., 2009; Heyradin et al., 2012; Molla et al., 2012). The majority of infected birds are infected with more than one species. The altitude and climatic conditions have been suggested to affect infection prevalence, with highland areas being linked to lower proportions of infected birds (Eshetu et al., 2001). However, neither Tolossa et al. (2009) nor Molla et al. (2012) found any such differences between different climactic regions. Although the proportion of positives may be high, parasites tend to be over-distributed, with around 10% of birds carrying large burdens which may have clinical

impact (Magwisha et al., 2002). Little work on the extent of the clinical impact of helminth infections in rural poultry appears to have been carried out. Weight loss or retarded growth, anaemia, weakness and mortality are known to be problems in experimental infections.

1.12 Cestodes

A brief description of some of the more important species of cestodes in Africa is given below, summarised from Permin and Hansen (1998) and McDougald (2008).

1.12.1 Davainea proglottina

A small worm - less than 4mm, with fewer than 9 proglottids – found in the duodenal mucosa. High burdens of over 3000 worms have been found in individual birds. The intermediate hosts are slugs and snails. This worm is pathogenic in young birds, causing reduced growth, emaciation and weakness.

1.12.2 Raillietina tetragona and Raillietina echinobothrida

These large worms (25-34 cm) are found in the small intestine and cause a hyperplastic nodular enteritis. Clinical signs include weight loss and decreased egg production. The intermediate host is the ant.

1.12.3 Raillietina cesticillus

This 15cm worm is found in the duodenum or jejunum, but is not thought to be pathogenic. Intermediate hosts are several beetle species.

1.12.4 Amoebotaenia sphenoides (Amoebotaenia cuneata)

This very small worm – less than 4mm – is found between the duodenal villi. The intermediate host is the earthworm. The exact pathogenic effects unclear, but infections are usually associated with haemorrhagic enteritis, or chronic wasting.

Chapter 1 | General introduction and thesis objectives 1.12.5 Choanotaenia infundibulum

This is a distinctive white worm, up to 23cm in length, found in the proximal intestines. It has several intermediate hosts including Musca (housefly) spp. and several beetles. It has been described as “moderately pathogenic” although there are no reported controlled experiments.

1.12.6 Hymenolopis cantainana

This is a very slender, thread-like worm, 2cm in length, found in the small intestines. Intermediate hosts are scarab (dung) beetles. It is not believed to be pathogenic.

1.12.7 Epidemiology

The level of cestode infections in village birds has been reported in studies in Ethiopia at values between 55 -86% (Ashenafi and Eshetu, 2004a; Tolossa et al., 2009; Heyradin et al., 2012; Molla et al., 2012). Variation between different regions with different altitude and climate conditions was reported, with three studies reporting lower proportions of infected birds in highland areas (Eshetu et al., 2001; Tolossa et al., 2009; Molla et al., 2012). Infection with multiple species was commonly reported. The more prevalent species are reported as R. tetragona, R. echinobothrida, A. sphenoides and H. cantainana. The more pathogenic D. proglottina has been reported at much lower rates of between 1% and 8%.