Morocco study identifies AEV in broiler outbreaks from 2020 to 2024

A new Frontiers in Veterinary Science report documents avian encephalomyelitis virus in six Moroccan broiler flocks affected between 2020 and 2024, giving the country its first published pathological and molecular characterization of these outbreaks. The affected birds were just 6 to 17 days old, and the investigators linked the cases to severe neurologic disease, with morbidity up to 90% and cumulative mortality above 25%. (frontiersin.org)

Avian encephalomyelitis is a well-known viral disease of poultry, but it tends to be most clinically apparent in young chicks, where tremors, ataxia, leg weakness, paresis, and recumbency are the hallmark signs. According to the Merck Veterinary Manual, vertically infected chicks often show disease in the first week after hatch, while horizontally infected chicks more often develop signs at 2 to 4 weeks of age. The disease has long mattered economically because even when mortality is limited, affected flocks can show substantial performance losses, and adult breeders can contribute to transmission if immunity is inadequate. (merckvetmanual.com)

In the Moroccan study, researchers evaluated six broiler flocks from multiple regions, including the Northern territories, Berrechid, Casablanca, Tit Mellil, and Beni Mellal. Histopathology showed multifocal gliosis, neuronal degeneration and chromatolysis, axonal degeneration, demyelination, and perivascular cuffing, with especially marked cerebellar lesions and Purkinje cell degeneration. RT-PCR detected AEV, and Sanger sequencing followed by phylogenetic analysis of the partial 5′-UTR placed four isolates in genotype B, close to the Hungarian strain pf-HK1, and two in genotype A. (frontiersin.org)

That genotype split is notable because the paper points to at least two evolutionary lineages circulating in Moroccan broilers rather than a single outbreak strain. The article also notes broader concern in the literature that divergent field variants can show meaningful genetic distance from vaccine strains, an issue that could become more important if surveillance uncovers wider spread or changing epidemiology. That said, the current study is descriptive, so it does not establish vaccine failure or quantify how these genotypes affect field protection. (frontiersin.org)

Industry-facing reference sources still frame prevention in familiar terms. Merck Veterinary Manual states there is no treatment for avian encephalomyelitis and that control relies on removing affected birds and vaccinating broiler breeder pullets to prevent vertical transmission and provide maternal immunity. Commercial products for breeder-age chickens remain available, including combination AE and fowl pox vaccines marketed for use before lay. (merckvetmanual.com)

Why it matters: For poultry veterinarians and diagnosticians, this paper is less about a brand-new pathogen than about sharpening case recognition and surveillance. Neurologic disease in very young broilers can quickly trigger concern for other infectious or nutritional causes, and Merck notes the differential list includes bacterial or mycotic encephalitis, neurotropic Newcastle disease, rickets, and nutritional encephalomalacia. The Moroccan findings reinforce the value of pairing flock history and age pattern with histopathology and molecular confirmation, especially in regions where AEV may be undercharacterized or masked by broader chick-quality and hatchery investigations. (merckvetmanual.com)

The report may also matter for production medicine beyond Morocco. If AEV is circulating in multiple lineages in commercial broilers, veterinarians may want to revisit breeder immunization records, maternal antibody assumptions, hatchery-linked epidemiology, and sample selection for neurologic cases. Merck specifically notes that brain, duodenum, and pancreas are important tissues for confirmation, and that not all published RT-PCR primer pairs amplify all isolates because of strain variation. (merckvetmanual.com)

What to watch: The next step is broader epidemiologic work, including serology, breeder-flock investigations, and expanded sequencing to determine whether these Moroccan detections represent sporadic spillover, endemic circulation, or a larger regional pattern. If more isolates are characterized, veterinary professionals will be watching for any evidence of shifts in transmission dynamics, diagnostic sensitivity, or vaccine match. (frontiersin.org)