Avian leukemia virus (ALV) is a type of cancer-causing retrovirus that is linked to tumorigenic disease, reduced fertility, and slowed growth in birds. It also leads to severe immunosuppression, making birds more susceptible to other infections and reducing the effectiveness of vaccinations against other diseases. The virus is mainly transmitted vertically from infected hens to their offspring through embryos, but it can also spread horizontally through direct or indirect contact with infected chickens or contaminated objects. Currently, there are no effective vaccines or treatments for this disease, so the most practical approach to controlling it is to identify and eliminate infected birds from the population.

Source: https://doi.org/10.1080/03079457.2011.646237

Clinical symptoms:

Infection with avian leukosis virus (ALV) can lead to the development of tumors, particularly lymphoid leukosi

s, in the liver, spleen, and bursa. In some cases, tumors may also be found in the kidneys and sex organs. The characteristics and frequency of these tumors depend on factors such as the specific strain of the virus, the breed of chicken, the age of the bird, and the method of infection.



Some of the clinical signs of this condition include:

• loss of appetite
• weakness
• diarrhea
• dehydration
• weight loss
• depression
• enlarged bursa and sometimes an enlarged liver

Infected birds may also lay fewer eggs, and while they may not necessarily develop tumors, they can still exhibit these symptoms.



Host immune response against Avian Leukosis Virus (ALV)

The host immune response against Avian Leukosis Virus (ALV) involves the innate immunity that acts as the first line of defense against invading pathogens. However, ALV has been found to suppress the host's innate immune response.

• Monocytes serve as the precursor cells of macrophages and dendritic cells (DCs), which are essential for both innate and adaptive immunity.
• Macrophages play a crucial role in innate immunity, and when activated by viruses, microbes, or cytokines, they are involved in pathogen clearance, immune regulation, and maintaining tissue integrity by secreting pro-inflammatory cytokines.
• DCs, as sentinel cells in the immune system, are vital for pathogen recognition, antigen presentation, and stimulation of T cells. In ALV-J-infected bone marrow-derived DCs (BM-DCs), cellular differentiation and maturation are effectively inhibited, leading to apoptosis due to the abnormal expression of microRNAs.

Diagnosis:

Standard criteria that include examining the patient's history and clinical signs, as well as gross pathological findings and histological examination.



In more advanced cases, additional criteria such as immunohistochemical testing, standard and quantitative PCR assay, virus isolation, and serological testing are also used.