Oropharyngeal trichomonads in wild birds

Oropharyngeal trichomonosis is a disease that affects wild and domestic birds. Some studies carried out in wildlife recovery centers pointed it out as the main cause of entrance of birds of prey due to infectious diseases. It causes small nodules and ulcers in the crop and other locations of the upper digestive system of the animals. These small lesions can coalesce and form large granulomas, which can provoke the death of the animal by starvation. Trichomonas gallinae is considered the etiological agent of the disease, a flagellated protozoon that is frequently found in the oral cavity of columbiformes, which are considered the main reservoir of the parasite. However, in the last decade, a great progress in the molecular characterization of this and other protozoa has been reached, and the number of genetic variants and even new species within the trichomonads that inhabit the avian oropharynx has expanded. In this review, we outline the latest descriptions of these parasites and their host spectrum; more than 10 genetic variants or new species are included. Although trichomonosis has been described in several groups of birds, the higher impact is usually found on Accipitriformes, Falconiformes and Strigiformes due to their predation or scavenging habits. Psittaciformes and Passeriformes also show clinical signs of the disease, and recently, several epidemic episodes of trichomonosis in fringilids were described across Europe and North America. In addition, chicks of endangered species like the Bonelli ́s eagle (Aquila fasciata) are frequently affected by the parasite, as several studies carried out in Spain and nearby countries have proved. In this chapter, we summarize the most important features of the disease, including the biology, the diagnosis and treatment options. Additionally, we will describe the recent scientific advances in the pathology, epidemiology and control of the disease. María Teresa Gómez Muñoz et al. 1. AVIAN OROPHARYNGEAL TRICHOMONOSIS Avian oropharyngeal trichomonosis is a parasitic disease that has been known for centuries. Although it has been described mainly in birds, there are some references about the presence of the parasitic process affecting even dinosaurs. First documented descriptions were found in falconry books, where the disease is explained as the appearance of typical lesions on birds of prey. For example, there is a book on falconry called “The hunting of birds”, from the 14 century, and the London's Turbervile book of 1575 in which the typical lesions are described. At first, the etiological agent was named Cercomonas gallinae (Rivolta, 1878). Later, in the year 1938, its taxonomic classification was reviewed by Dr. Robert M. Stabler, from the University of Colorado. He is one of the authors who has contributed most to knowledge about avian trichomonosis through numerous scientific publications. Since then, other scientists, especially in the United States, have been responsible for studying different aspects related with pathogen mechanisms, morphology, immunology, biology, and protozoan treatment. Some of the scientists to be highlighted are: Dr. Richard M. Kocan, from the US Bureau of Sport Fisheries and Wildlife, Patuxent wildlife research center, Laurel, Maryland; Dr. Bronislaw M. Honigberg, from the University of Massachusetts; Dr. Norman D. Levine from the University of Illinois and Dr. Lionel G. Warren, from Rice University, Houston, Texas, among others. Trichomonosis is one of the most relevant infectious diseases among wild birds, both from urban (Boal et al., 1998; Stenkal et al., 2013) and rural environments. Raptors are the most frequently reported with the disease in the studies carried out. Wendell et al., in 2002, analyzed the causes of admission to the Veterinary Hospital of Colorado University (USA) in a retrospective study from 1995 to 1998. Trichomonosis accounted for 44% among the infectious diseases in raptors and it was the second cause of admission in importance after trauma. In a different study carried out in Spain, the authors found the same percentage of trichomonosis among the infectious diseases in raptors, being Strigiformes and Falconiformes the most affected (Molina-López et al., 2011). Remarkably, the disease has been considered emergent in passeriformes since 2005 (Pennycot et al., 2005) and it has spread out through Europe and America, being a cause of population decline. 2. THE AGENT: TAXONOMY, MORPHOLOGY, LIFE CYCLE AND