Anatid alphaherpesvirus 1

Did You Know?

• Resveratrol has shown some antiviral activity against DEV.
• It took 300,000 times more virus material to infect a northern pintail than a blue-winged teal.
• DEV is considered pantropic, replicating in multiple organs and increasing vascular permeability.

Clinical signs and diagnosis

The incubation period for domestic fowl is 3–7 days, and up to 14 days for wildfowl. A sudden and persistent increase in flock mortality is often the first observation. Individual birds may show loss of appetite, decreased egg production (20–40% reduction), nasal discharge, increased thirst, diarrhea, ataxia, tremors, a drooped-wing appearance, and in males a prolapsed penis. Death usually occurs within 5 days after symptom onset.

Clinical signs vary with virus strain virulence, species, sex, and immune status. Diphtheroid plaques on eyelids and mucosae of the respiratory and gastrointestinal systems may cause ophthalmic signs and refusal to drink. DEV infects only birds of the family Anatidae (order Anseriformes), with a possible exception of coots (order Gruiformes) based on lesion similarities. Waterfowl species differ in susceptibility; blue-winged teal are among the most susceptible, mallards among the least.

Diagnosis is usually made from clinical signs and postmortem findings: petechial hemorrhage in conjunctivae, mucous membranes, trachea, syrinx, and intestine is pathognomonic. Confirmation can be via virus inclusion bodies in tissues or positive immunohistochemical staining for viral antigen.

Epidemiology

DEV occurs during spring seasons globally. In the United States, Netherlands, and UK, most outbreaks happen from March to June; in the Southern Hemisphere, such as Brazil, outbreaks occur November through February. Survivors of primary infection enter a latent stage lasting up to 4 years. Latent carriers shed virus in shared water or through direct contact (horizontal transmission), and there is evidence of vertical transmission to eggs and offspring, which remain asymptomatic. Stress—such as migration, breeding season, or social interaction—can trigger shedding and induce herpetic lesions. Primary latency sites include the trigeminal ganglion, lymphoid tissue, and blood lymphocytes.

Virology

DEV is classified as the species Mardivirus anatidalpha1 in the genus Mardivirus, subfamily Alphaherpesvirinae, family Herpesviridae, order Herpesvirales. Three genes have no homologs in other herpesviruses. The genome is arranged as UL-IRS-US-TRS and encodes 78 predicted proteins. Morphology includes a DNA core, icosahedral capsid, tegument, and envelope; the nucleocapsid is 75 micrometers wide and the envelope diameter 181 micrometers. Transcription occurs in three phases: immediate early (IE), early (E), and late (L). IE genes are transcribed without other proteins; E genes depend on IE products. Virions attach to cells using glycoprotein spikes (gB, gC, gD, gH, gL). gC aids binding, gD stabilizes, and gB, gD, gH, gL enable fusion.

History

The first known duck plague outbreak, caused by Anatid alphaherpesvirus 1, occurred in the Netherlands in 1923. In the United States, the disease first appeared on Long Island, New York, severely harming the local duck industry. Another major U.S. outbreak happened in 1973 at Lake Andes, South Dakota, killing 43,000 birds. By 2005, the World Organisation for Animal Health stopped requiring reports of the virus, citing little evidence of international spread and a low risk to human health. Still, economic worries persist in poultry-dependent areas like India.