With the rapidly increasing demand for poultry products and the current challenges facing the poultry industry, the application of biotechnology to enhance poultry production has gained growing significance. Biotechnology encompasses all forms of technology that can be harnessed to improve poultry health and production efficiency. Notably, biotechnology-based approaches have fueled rapid advances in biological research, including (a) genetic manipulation in poultry breeding to improve the growth and egg production traits and disease resistance, (b) rapid identification of infectious agents using DNA-based approaches, (c) inclusion of natural and synthetic feed additives to poultry diets to enhance their nutritional value and maximize feed utilization by birds, and (d) production of biological products such as vaccines and various types of immunostimulants to increase the defensive activity of the immune system against pathogenic infection. Indeed, managing both existing and newly emerging infectious diseases presents a challenge for poultry production. However, recent strides in vaccine technology are demonstrating significant promise for disease prevention and control. This review focuses on the evolving applications of biotechnology aimed at enhancing vaccine immunogenicity, efficacy, stability, and delivery.

Avian encephalomyelitis (AE) is a disease caused by the avian encephalomyelitis virus (AEV) of the genus Tremovirus in the family Picornaviridae. Recently, cases of turkey poults showing neurological signs were submitted to the veterinary diagnostic laboratories at South Dakota State University and the University of Minnesota. The affected birds were showing nervous neurological signs such as tremors, inability to stand, torticollis, and wing drop. Clinical signs were observed by 3 weeks of age. Necropsy of birds revealed no significant gross lesions in the internal organs, including the brain. There was no significant bacterial growth in the brains. Microscopic examination of various sections of the brain revealed multifocal lymphocplasmacytic perivascular cuffs in the cerebellum and cerebral cortex. The brain samples were processed for detection and whole genome sequencing by next-generation sequencing. Three full-length polyprotein sequences (6405 nt) of AEV were assembled. All three sequences shared 99.9–100% nucleotide and 100% amino acid identities with each other. Only 77.7–78.5% of nucleotide and 90.3–92.5% of amino acid identities with AEV field strains and vaccine sequences were available in GenBank. This indicates that a new divergent variant of AEV is circulating in the field and causing AE outbreaks in the Midwest region.

The recent ongoing outbreak of avian metapneumovirus subgroup B (aMPV-B) in the United States represents a serious threat to turkey and chicken production. In this study, we used the aMPV-B/chicken/USA/SD-24/P6 isolate to test pathogenicity and to establish a challenge model in chickens and turkeys. Two studies were conducted in both species: in 7- and 14-day-old chickens and in 1-, 7-, and 14-day-old turkeys. We inoculated two challenge doses: 10³ and 10⁵ 50% tissue culture infectious doses. All challenged birds were monitored for clinical signs, gross lesions, histopathologic lesions, as well as virus shedding for 7 days postchallenge (DPC). Each challenged chicken and turkey showed clear clinical signs, as well as gross and histopathologic lesions, along with virus shedding with no noticeable variations related to age or challenge dose. The inoculated virus demonstrated high pathogenicity in both chickens (the host of origin) and turkeys, indicating no host specificity. The highest virus shedding occurred at 3 and 5 DPC in all challenge groups across both species. To our knowledge, this study is the first in the United States to fulfill the Koch's postulates for aMPV-B by experimentally reproducing clinical disease in both chickens and turkeys using a U.S. field strain, followed by successful reisolation of the virus from infected tissues. These challenge models will be helpful for evaluation of the efficacy of imported and new vaccines.

Respiratory viral diseases infecting poultry lead to variable lesions in the respiratory organs, including nasal sinuses, trachea, lungs, and air sacs. Additional involvement of eyelids/conjunctiva was reported. The distribution and the intensity of lesions depend on multiple factors, including virulence, the host’s immunity, and secondary or concurrent infections. It may be challenging to detect remarkable lesions during experimental infections conducted in a controlled environment because some viruses fail to produce the intense lesions seen in field cases. This creates a challenge in developing a reliable model to study pathogenicity or vaccine efficacy experimentally. The development of the proposed histologic respiratory index (HRI) aims to help monitor the least microscopic changes that can be scored, thereby creating an objective and accurate grading of lesions in experimentally infected birds. HRI scores the changes in eyelids/conjunctiva and respiratory mucosa, including hyperplasia, metaplasia, inflammatory cellular infiltration in the submucosa, including lymphocytes and heterophils, and vascular changes (vasculitis) in nasal sinuses, trachea, and lungs. The score was validated in birds infected experimentally with avian metapneumovirus (aMPV) and low pathogenic avian influenza (LPAI-H4N6). The HRI reliably graded higher scores in the respiratory organs of experimentally infected birds compared with non-infected control ones. The HRI is the first of its type with poultry viral respiratory pathogens and it was initially proven to be a reliable in pathogenicity and vaccine trials of certain poultry respiratory viral diseases.

La hibridación in situ para estudiar la patogenicidad de los subtipos A y B del metapneumovirus aviar norteamericano en pavos. El metapneumovirus aviar (aMPV) es un patógeno altamente contagioso del tracto respiratorio superior que causa importantes pérdidas económicas tanto en pollos como en pavos. A nivel mundial, existen cuatro subgrupos antigénicamente distintos: A, B, C y D, basados en la secuencia de la glicoproteína G. Los subgrupos A y B surgieron recientemente en Estados Unidos, causando varios brotes en pollos y pavos, con altas tasas de morbilidad y mortalidad, así como una disminución en la producción de huevo. El metapneumovirus aviar infecta principalmente el tracto respiratorio superior, los párpados y conjuntiva. La hibridación in situ (ISH) es una herramienta molecular que localiza secuencias específicas de ácidos nucleicos dentro de células o tejidos. Se diseñaron sondas para hibridación in situ para detectar el gene N, altamente conservado, de los subtipos A y B del metapneumovirus aviar, localizando el ácido nucleico del virus a nivel celular en el tracto respiratorio, lo que permite visualizar los sitios de unión y replicación viral. Se sometieron a hibridación in situ diferentes tejidos de pavos positivos por rRT-PCR. Los pavos afectados mostraron un aumento de la morbilidad y la mortalidad, que coincidió con signos clínicos y lesiones de sinusitis catarral, rinitis y conjuntivitis. Los senos infraorbitarios, los cornetes nasales y la conjuntiva fueron los tejidos más afectados. Además de la detección del metapneumovirus aviar, se detectaron infecciones bacterianas secundarias. Las sondas diseñadas identificaron la diseminación del metapneumovirus a lo largo de la mucosa respiratoria superior, incluyendo los senos nasales/infraorbitarios, la tráquea y los bronquios secundarios. También mostraron la presencia del virus en las secreciones luminales del tracto respiratorio superior. Este trabajo describe la distribución y la excreción viral en los órganos respiratorios de pavos de engorde comerciales infectados naturalmente con metapneumovirus aviar en condiciones de campo. Estos resultados contribuyen a la comprensión de la patogénesis del metapneumovirus aviar y confirman la mejor estrategia de muestreo para el diagnóstico.

Reporte de caso - Impacto de los reovirus de pavo en el rendimiento de las parvadas de pavos comerciales: Un diagnóstico e investigación de campo. Los reovirus asociados con artritis de pavos imponen una gran amenaza a los pavos comerciales con la inducción de tenosinovitis/artritis y hepatitis, lo que ha resultado en pérdidas económicas sustanciales. La aparición del reovirus de la hepatitis de pavos se informó en 2019 y causó mortalidad entre los pavitos jóvenes. Investigamos un caso de infección por reovirus de la hepatitis de pavos en una parvada de pavipollos y se dio seguimiento a esa parvada hasta la edad de comercialización para evaluar la influencia de la infección en el rendimiento de la parvada. La parvada infectada mostró tenosinovitis con una influencia negativa en el rendimiento de la parvada, incluida reducción en la ganancia diaria de peso promedio y el peso promedio de comercialización. El reovirus se aisló del hígado de las parvadas infectadas y, posteriormente, se aisló de los tendones de las aves de la misma parvada. La secuenciación del genoma completo y el análisis de la secuencia de los aislamientos hepáticos y artríticos revelaron que están estrechamente relacionados. Además, se comparó el rendimiento de esta parvada con otras parvadas infectadas con el reovirus de la artritis del pavo y se estableció una comparación genómica. Nuestra investigación de campo mostró que el reovirus de la hepatitis del pavo puede inducir tenosinovitis y tiene un mayor impacto en el rendimiento de la parvada en comparación con el impacto de reovirus asociados con la artritis del pavo.