Preliminary testing in turkeys of the safety and efficacy of a putative haemorrhagic enteritis virus vaccine

Turkey Hemorrhagic Enteritis (THE): A Short Overview

Turkey Hemorrhagic Enteritis (THE) is an acute disease caused by a Siadenovirus that affects 4 week-aged and older turkeys, characterized by acute depression, bloody droppings, and a high mortality rate. The immunosuppressive attributes of THE can protract disease progression and create a predisposition in birds towards subsequent bacterial infectiodoralns involving Escherichia coli and Clostridium perfringens (necrotic enteritis). Turkey Hemorrhagic Enteritis Virus (THEV) predominantly affects turkeys and carries substantial economic implications for this industry. Macrophages and B lymphocytes are recognized as the predominant target cells for the virus, while the spleen is the principal site of viral replication. Infected cells have also been observed in various other tissues, including the intestines, bursa of Fabricius, cecal tonsils, thymus, liver, kidney, peripheral blood leukocytes, and lungs. The economic relevance of this disease is derived both from the high mortality rate, which can reach 60% depending on the virulence of the strain, and from subclinical disease responsible for poor performance in vaccinated animals. This review aims to provide a comprehensive overview of THE, spanning etiology, epidemiology clinical signs and gross lesions, prevention, and management.

Animal experiments show impact of vaccination on reduction of SARS-CoV-2 virus circulation: A model for vaccine development?

BACKGROUND

In the pre-clinical phase, SARS-CoV-2 vaccines were tested in animal models, including exposure trials, to investigate protection against SARS-CoV-2. These studies paved the way for clinical development. The objective of our review was to provide an overview of published animal exposure results, focussing on the capacity of vaccines to reduce/prevent viral shedding.

METHOD

Using Medline, we retrieved eighteen papers on eight different vaccine platforms in four animal models. Data were extracted on presence/absence of viral RNA in nose, throat, or lungs, and neutralizing antibody levels in the blood.

RESULTS

All vaccines showed a tendency of reduced viral load after exposure. Particularly nasal swab results are likely to give an indication about the impact on virus excretion in the environment. Similarly, the reduction or prevention of viral replication in the bronchoalveolar environment might be related with disease prevention, explaining the high efficacy in clinical trials.

DISCUSSION

Although it remains difficult to compare the results directly, the potential for a strong reduction of transmission was shown, indicating that the animal models predicted what is observed in the field after large scale human vaccination. This merits further attention for standardization of exposure experiments, with the intention to speed up future vaccine development.