Main protozoan diseases in turkeys
The name ‘proto-zoa‘ literally means ‘first animals’ and the first classification systems grouped the protozoa as basal members of the Animal Kingdom. Protozoa have been classified more recently along with several groups of algae and fungi in the Protista Kingdom. There are numerous protozoa that affect turkeys, but some of the main protozoan diseases in turkeys are particularly important for the consequences caused in the breeding of this species.
Protozoa are eukaryotic organisms, which exist as structurally and functionally independent individual cells (including those gregarious species). None has adopted the multicellular somatic organization characteristic of metazoans. Instead, protozoa have developed relatively complex subcellular characteristics, such as membranes and organelles, which allow them to survive their environments. Most protozoa are microscopic organisms, and being unicellular eukaryotes show the same essential life activities as higher metazoan eukaryotes: they move to survive, feed and reproduce.
Frecuent protozoan diseases in turkeys
Histomoniasis is also known as Blackhead disease because of the typical external symptomatology that it produces. Its etiological agent is the flagellated protozoan Histomonas meleagridis. This parasite uses an intermediate host, which are the eggs of the nematode Heterakis.
Turkeys are more susceptible when they are between 3 and 12 weeks old. Symptoms of this disease appear between 7 and 12 days after infection, and include depression, inappetence, polydipsia, impaired growth, deficient plumage and smelly and sulphur-colour diarrhoea. Anatomically, it is characterized by a caseonecrotic typhohepatitis and a cyanotic or blackish-blue coloration of the region of the head.
There is a tendency to an acute presentation in younger turkeys, with very high mortality, up to 90% of the animals, with morbidity close to 100%. In the chronic form, which affects older turkeys, chronic enteritis occurs, alternating constipation and diarrhoea, transforming the animals into chronic carriers, with high productive losses and mortality.
Hexamitiasis is a protozoan disease caused by Hexamita meleagridis and characterized by a catarrhal enteritis. This appears at the three months of life mainly, being the mortality especially high between the first and the ninth week of life. Its symptoms are nonspecific, finding animals with altered plumage, worsening of conversion rate and weight gain, and presenting a profuse watery or foamy diarrhoea.
Regarding the lesions, catarrhal enteritis is observed in the three portions of the small intestine, with dilations of the intestinal wall with abundant aqueous content, and the parasites adhered to the epithelial cells of the Lieberkühn crypts.
Trichomoniasis is another parasitosis caused by a flagellated protozoan; in this case the agent is Trichomonas gallinae. Although turkeys are not the most affected species, they are susceptible to suffer from this disease, being especially serious in poults.
The disease appearance begins with anorexic birds, apathetic, with crawling content. It mainly affects the upper digestive tract, with caseous masses distributed throughout the mucosa. It begins as yellowish lesions in the oral cavity that extend forming those masses of caseous growth through the palate, oesophagus and rest of the anterior digestive tract.
Although it is not very frequent, it can sometimes reach the last portion of the digestive tract producing enteritis with associated yellowish diarrhoea, and a hepatitis with granular lesions of caseous content.
Different species of Cochlosoma genus have been described, but the one that seems to be more frequent is Cochlosoma anatis. It affects the intestine causing atrophy and catarrhal enteritis. In poults can cause high mortality, but the most frequent problem is in adults where most cases of infestation are subclinical with a significant reduction in production parameters.
Amebiasis is a dysenteric process that mainly affects turkeys in the first weeks of life. The most frequent manifestation takes place between the months from August to September. The microscopic observation of the mucosa and intestinal contents allows the observation of cysts with 2 or 3 nuclei, and this technique is important for an adequate diagnosis since sometimes this parasitosis can occur together with secondary microorganisms such as E. coli.
Coccidiosis is a protozoan disease caused by microorganisms of Phylum Apicomplexaand specifically of the family Eimeriidae. In Turkey, species such as Eimeria meleagrimitis, E. meleagridis, E. dispersa or E. gallopavonis, among others, have been described as etiological agents. The disease originates after the ingestion of sporulated oocysts, which provoke to a clinical or subclinical process whose most frequent characteristics are usually general depression, decreased feed intake, bristling feathers, diarrhoea that can range from watery to bloody and the worsening of the productive parameters.
The severity of this disease will depend on different factors such as age, immune status, sanitary conditions of the birds, the number of oocysts or the Eimeriaspecies involved.
Lesions and clinical signs are often less evident than in chickens; sometimes those lesions resolve quickly and, therefore, at necropsy cannot detected. The disease is most evident in young turkey poults between 6-8 weeks old as it is believed that exposure at an early age develops resistance. Morbidity rates are high in young birds and mortality rates vary widely depending on the species of Eimeria, the occurrence of concurrent infections, age and other factors.
Scarcity of treatments and the importance of good farm management practices
The aforementioned main protozoan diseases in turkeys are of diverse symptomatology and course. They influence very negatively in the productive parameters and, therefore, in the economy of the farms. Its treatment becomes a very complicated practice, since the chemotherapeutic substances for many of these diseases are either prohibited by legislation or are toxic to birds. Accordingly, the spectrum of treatments is really small.
Good management practices that include deworming programs, to eliminate the vectors of some of the parasites described, adequate biosecurity measures and pronutrient-based therapies (bioactive molecules from plant extracts that improve animal physiology to self-limit the infestation). These are the methods that can be considered more effective and offer greater guarantees in the face of recent legislation, which is increasingly restrictive, regarding the use of chemotherapeutics.