Israel turkey meningoencephalitis virus (family Flaviviridae, genus Orthoflavivirus) has been reported only in turkeys. It causes progressive paresis and paralysis with decreased egg production and variable mortality. Diagnosis is by viral isolation and identification by ELISA, PCR assay, and serological testing. No specific treatment is available, so control is based on preventing exposure to insect vectors and vaccination.
Israel turkey meningoencephalitis generally occurs only in birds > 10 weeks old. Although the specific vector has not been identified, the seasonal incidence and sporadic occurrence in flocks on the same farms strongly suggest it is transmitted by insect vectors, most likely mosquitoes and Culicoides midges. The virus has been detected only in Israel and South Africa.
The complete nucleotide sequences of Israel turkey meningoencephalitis virus isolates suggest that this virus is closely related to another flavivirus, Bagaza virus (Orthoflavivirus bagazaense). The reports of at least two studies propose that Israel turkey meningoencephalitis virus and Bagaza virus are the same virus species, based on full genome sequence comparisons, although currently, both viruses are listed by the International Committee on Taxonomy of Viruses (1, 2).
Bagaza virus has been detected in western and South Africa, India, the Arabian Peninsula, Portugal, and Spain. Bagaza virus causes listlessness and neurological clinical signs similar to those of Israel turkey meningoencephalitis virus in game birds, including domestic turkeys and some captive and wild pheasants and partridges.
Clinical Findings in Israel Turkey Meningoencephalitis Virus in Birds
Turkeys with Israel turkey meningoencephalitis exhibit neurological dysfunction characterized by progressive paresis and paralysis, with variable mortality rates. Morbidity and mortality rates average 15%–30% but may be as high as 80%. In turkey breeder hens, egg production drops severely.
Lesions
Gross lesions in turkeys with Israel turkey meningoencephalitis include splenomegaly or atrophy of the spleen, catarrhal enteritis, and myocarditis. The principal microscopic lesions are nonpurulent meningoencephalitis characterized by submeningeal and perivascular lymphocytic infiltration and focal myocardial necrosis.
Diagnosis of Israel Turkey Meningoencephalitis Virus in Birds
Laboratory diagnosis of Israel turkey meningoencephalitis is based on the same procedures as those used for eastern equine encephalitis virus.
Prevention and Control of Israel Turkey Meningoencephalitis Virus in Birds
No specific treatment for Israel turkey meningoencephalitis is available. It is best prevented by measures designed to decrease vector populations (ie, most likely flying vectors but not definitively identified) and by locating production facilities away from vector habitats.
Transmission and disease also may be controlled by vaccination. A live, attenuated virus vaccine has been prepared by serial passage of virus in Japanese quail kidney cells; this vaccine is highly efficacious and commercially available.
Key Points
Israel turkey meningoencephalitis is a disease of turkeys characterized by neurological disease, with variable mortality and decreased egg production. No species other than turkeys is known to be affected.
Diagnosis is by virus isolation and identification by ELISA, PCR assay, and serological testing.
Control of Israel turkey meningoencephalitis virus infections is based on decreasing exposure of susceptible turkeys to vectors. An efficacious commercially available live vaccine can be used for immunization.
Israel turkey meningoencephalitis virus is not known to be pathogenic in humans.
References
Falcão M, Barros MC, Duarte MD, et al. Genome characterization and spaciotemporal dispersal analysis of Bagaza virus detected in Portugal, 2021. Pathogens. 2023;12(2):150. doi:10.3390/pathogens12020150
Fernández-Pinero J, Davidson I, Elizalde M, Perk S, Khinich Y, Jiménez-Clavero MA. Bagaza virus and Israel turkey meningoencephalomyelitis virus are a single virus species. J Gen Virol. 2014;95(Pt 4):883-887. doi:10.1099/vir.0.061465-0
