Avian leukosis virus (ALV)

Test code: S0262 - Ultrasensitive qualitative detection of avian leukosis virus by reverse transcription coupled real time polymerase chain reaction

Avian leukosis virus (ALV) is a retrovirus belonging to the family retroviridae, genus alpharetrovirus. It is a single-stranded RNA virus with a genome of about 7.6–8.3 kb and can integrate into the cellular genome as a proviral latent virus. There are 10 subgroups (A–J) of this virus based on envelope glycoproteins, host range, and receptor usage.

This virus primarily affects chickens. Infection of other avian species like turkeys, pheasants, or quail can occur, but it is not common. This virus spreads vertically (from hen to egg, via germinal cells) and horizontally (through contact with infected saliva, feces, or secretions). Vertical transmission is the most economically damaging, as it perpetuates infection across generations. Infection by this virus is therefore a significant concern in poultry production because this virus can cause tumor formation, immunosuppression, and ultimately production losses. Clinical symptoms may include enlarged liver, spleen, and bursa, but many infected chickens do not show obvious symptoms and subclinical infections are widespread, causing reduced egg production, hatchability, and growth rates. Symptoms of infected chickens also overlap with those caused by Marek’s disease virus or avian reticuloendotheliosis virus.

Clinical signs and histopathology are not useful to differentiate this disease from other infections. Serological screening of chickens can detect ALV antigens (e.g., p27 capsid protein) in cloacal swabs and egg albumen, but serology may also pick up the endogenous ALV antigen to give a false positive result (Pham et al., 1999). PCR has high sensitivity and specificity, and is the most reliable means to diagnose chickens infected with this virus (Pham et al., 1999; Gopal et al., 2012).

Utilities:

• Help confirm the disease causing agent
• Environmental monitoring
• Help ensure that bird populations are free of ALV
• Early prevention of spread of the virus among bird populations
• Minimize human exposure to the virus
• Safety monitoring of biological products and vaccines that derive from birds

References:
Pham, T.D., Spencer, J.L., Traina-Dorge, V.L., Mullin, D.A., Garry, R.F. and Johnson, E.S. (1999) Detection of exogenous and endogenous avian leukosis virus in commercial chicken eggs using reverse transcription and polymerase chain reaction assay. Avian Pathol. 28:385-392.

Gopal, S., Manoharan, P’, Kathaperumal, K., Chidambaram, B. and Divya. K.C. (2012) Differential detection of avian oncogenic viruses in poultry layer farms and Turkeys by use of multiplex PCR. J. Clin. Microbiol. 50:2668-2673.

Specimen requirements: 0.2 ml feces, or cloacal swab, or tracheal swab, or 0.2 ml whole blood in EDTA (purple top) tube, or 0.2 ml fresh or frozen tissue, or 0.2 ml cell culture.

Contact Zoologix if advice is needed to determine an appropriate specimen type for a specific diagnostic application. For specimen types not listed here, please contact Zoologix to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology: Qualitative reverse transcription coupled real time PCR

Normal range: Nondetected