Toxoplasmosis is a zoonotic (can be transmitted from animals to humans) parasitic protozoan disease and is rare in poultry. It is more common in aviaries and backyard poultry than commercial producers. It is characterised by disorders of the central nervous system but can also affect reproductive, musculoskeletal (muscles and bones) and visceral organs (internal organs of the chest and abdomen). Clinical signs in poultry include weight loss, inappetence, shrunken comb, drop in egg production, whitish diarrhoea, incoordination, trembling, opisthotonos (severe spasm in which the back arches), torticollis (twisting of the neck) and blindness. All chickens infected before eight weeks of age develop clinical signs. In older birds, infection can be asymptomatic (infected hosts show no symptoms) or latent (symptoms only develop under certain conditions).
Toxoplasmosis is caused by the parasitic protozoa Toxoplasma gondii. Cats are the only definitive hosts (a host in which the parasite can sexually reproduce) and so both wild and domestic cats serve as the main reservoir of infection. There are three infectious stages in the lifecycle of this protozoa. Stage one is within the tissue of the host, stage two is when the protozoan is excreted by the host in the faeces and stage three is when the protozoan transferred across the placenta in mammals to their offspring. Transmission can therefore occur by eating infected tissue, contact with infective faeces or transfer from an infected mother to a developing foetus (in mammals only).
Drugs are available that suppress multiplication of the parasite within the host but they will not usually eradicate the infection. Good biosecurity and management procedures are the principle forms of control in commercial poultry flocks. Pet animals should be kept away from poultry and poultry feed. Establish good rodent control and use separate staff for infected and uninfected flocks. Infected flocks should be depopulated as soon as possible after diagnosis is confirmed. Oocysts (the spore-like infective stage of the lifecycle that is passed in the faeces of the infected host) are resistant to detergents, acids and alkalis. Effective methods of disinfection include steam cleaning, ammonia, drying and heating (to 55oC for 24 hours). Concrete floors assist disinfection. Buildings should remain empty for four weeks after cleaning and disinfection.