Parasitic Diseases of Poultry

Poultry products are one of the most important protein sources for man throughout the world. Increasingly, and especially in urban areas, these poultry products are derived from intensive production, with control of parasitic infections through the use of veterinary medication and good sanitation. In intensive battery systems, control of parasites is also by through a high degree of isolation from potential disease causing organisms, carriers and vectors. Scavenging, backyard and free ranging poultry production systems have, by definition, a much greater degree of contact with potential disease causing organisms. Especially in scavenging and backyard systems, disease prophylaxis is uncommon. A number of parasites are widely distributed in developing countries and they contribute to a lower productivity in these traditional production systems.

Internal Parasites External Parasites Diseases caused by Protozoa Haemoparasites (Blood Parasites) References and Further Reading

Nematodes are the most common and most important helminth species in poultry. More than 50 species have been described in poultry, and the majority of these can cause pathological damage to the host. The majority of nematode species live in the intestines but a few species may occur in other parts of the body.

Cestodes (tapeworms) are also found in poultry, and those reared under free range, scavenging or backyard conditions are more likely to be infected with them. The tapeworms require an intermediate host, such as earthworms or insects. Birds become infected after ingestion of an infected intermediate host.

Trematodes (flukes) can be found in chickens but are most commonly encountered in ducks, since the life cycles of trematodes normally involve snails or other molluscs in aquatic environments.

The ectoparasites are Arthropods and are divided into two main classes:

• The Arachnida (arachnids) including the order Acari (ticks and mites)
• The Insecta including the orders Phthiraptera (lice), Hemiptera (bugs), Siphonaptera (fleas) and Diptera (flies and mosquitoes).

Ectoparasites are common under free-range and scavenging systems, but are usually controlled (although not eradicated) in intensive commercial systems. If measures are not taken to control ectoparasites in intensive systems. the high density of birds will inevitably lead to very severe outbreaks of infestation.

Ectoparasites may constitute a clinical problem in themselves, but may also transmit a number of infectious diseases to poultry, such as Pasteurella or Fowl Cholera, Aegyptinella spp., Borrelia anserina, Plasmodium spp., Leucocytozoon spp., Newcastle Disease, Fowl pox. Ectoparasites may act as vectors of a range of intermediate hosts which may also cause disease symptoms, but at the same time carry additional disease causing organisms, such as the eggs of Heterakis gallinarum carrying Histomonas meleagridis.

Mites can be particularly troublesome. The red mite comes out at night from small cracks and other refuges near perching areas and feeds on perching birds. At high levels of infestation, attacks by the mite can cause increased stress to the birds and subsequently reduced egg production, anaemia and in severe cases, death. They have also been implicated as vectors of several significant disease organisms such as chicken pox virus, Newcastle virus and fowl typhoid. Mites are also responsible for scaly leg.

Poultry kept in free range systems or on pastures are exposed to a number of vectors that transmit protozoa and other blood parasites. The haemoparasites or blood parasites are mainly found in poultry in tropical areas and the following genera Plasmodium spp., Leucocytozoon spp., Haemoproteus spp., Aegyptinella spp., Eperytrozoon spp., Trypanosoma spp. and microfilaries of nematodes belonging to the suborder Filariata have been recorded in poultry. Over 10 species of these are of pathogenic and economic importance.

Protozoa are common in poultry and may produce moderate to severe clinical symptoms. Coccidiosis is probably the most widespread and important parasitic disease in commercial as well as backyard poultry operations and as such responsible for major economic losses in the poultry industry.

Protozoa important in poultry production
(adapted from: Permin and Hansen 1998)

Coccidiosis

Coccidiosis is caused by protozoan parasites, belonging to the genus Eimeria that live in the lining of the intestine. Both indoor and outdoor poultry management systems are at risk, but those that reply on intensive systems of production, with large numbers of birds in a small space are most at risk. Under such conditions serious infections can quickly build up. Typically, the disease is seen in birds of 3-6 weeks old, before they have acquired immunity. Different species of the parasite may infect different livestock. For example, the coccidia infecting chickens are not thought to pass infections to sheep, and vice versa.

Healthy adult animals tend to have some immunity to coccidia. Similarly, local breeds are more likely to have some resistance than imported exotic breeds. The most susceptible animals are chicks and young birds. Adults can also develop coccidiosis if they are stressed or if they are moved into a new environment that is heavily infested with oocysts. Coccidiosis is also more of a problem in crowded conditions.

Treatment can be provided by a class of drugs called coccidiostats. These drugs tend to slow down the disease rather than kill all the coccidia, and they will also help reduce the number of oocysts that are being passed into the environment.

Histomoniasis or Blackhead

Hostomoniasis is a severe protozoan disease primarily causing problems in turkeys, but it can also affect chickens and other poultry. Chickens tend to be more resistant to Blackhead, and may not show symptoms, and this is one reason why they should not be kept together with turkeys. Blackhead is caused by the protozoan organism Histomonas meleagridis which damages the caecal wall. Secondary infection occurs with coliform bacteria Clostridium perfringens, Escherichia coli and other bacterial pathogens, and it is suggested that these are responsible for the disease symptoms. Infection may also spread to the liver resulting in yellow droppings.

Histomonas meleagridis is carried and introduced to poultry in the eggs of the caecal nematode worm, Heterakis gallinae. In the egg of this nematode it can survive in the environment for up to about four years. Birds with lowered resistance due to factors such as fowl pox or nutritional diseases are more severely affected.

Infected birds produce droppings which are heavily contaminated with the organism. Adolescent and adult birds are not infected by eating these droppings as Histomonas is normally killed by the acids in the proventriculus and gizzard. Birds only become infected by eating caecal worm eggs which transport Histomonas safely through these parts of the digestive system. Droppings containing contaminated eggs of the nematode worm can therefore result in rapid spread of the disease among young growing birds. Successful control of blackhead relies on the removal of the nematode worm eggs from the cycle (e.g. using anti-nematode drugs), and at the same time providing areas that are not contaminated by Histomonas. The survival of the nematode worm eggs in the environment can be reduced by providing sunny and well-drained facilities.

 

Permin, A. (1997). Helminths and Helminthosis in Poultry with Special Emphasis on Ascaridia Galli in Chickens. PhD Thesis. Danish Centre for Experimental Parasitology & Department of Veterinary Microbiology, The Royal Veterinary and Agricultural University, Copenhagen, Denmark