Infectious laryngotracheitis diagnosed in laying chicken
By Martin D. Ficken, DVM, PhD, DACVP, DACPV
With over 800,000 tests run annually, TVMDL encounters many challenging cases. Our case study series will highlight these interesting cases to increase awareness among veterinary and diagnostic communities.
A 12-month-old black and white female laying chicken from a small backyard flock was received for necropsy. The owner had elected euthanasia of this bird following a clinical exam revealing acute abnormal respiration including open mouth breathing. Another bird in the flock had similar clinical symptoms and had died. Following euthanasia and refrigeration, the bird was submitted by the referring veterinarian to the Texas A&M Veterinary Medical Diagnostic Laboratory in Gonzales, Texas for necropsy.
Necropsy revealed changes only within the trachea. Blood and fibrinous exudate were present in the upper one-third of the trachea. The underlying mucosa had a roughened appearance. Microscopically sections of trachea had extensive exudation of red blood cells, fibrin, heterophils, and macrophages into the tracheal lumen (Figure 1). Many degenerating epithelial cells contained eosinophilic intranuclear inclusions (Figure 2) characteristic of avian herpesvirus. The lamina propria contained large numbers of lymphocytes and plasma cells. Polymerase chain reaction (PCR) evaluation of tracheal swabs was positive for infectious laryngotracheitis virus.
Infectious laryngotracheitis (ILT) is a respiratory tract infection of chickens caused by Gallid herpesvirus type 1 (GaHV-1). The virus may cause severe production losses due to mortality and/or decreased egg production. Severe epizootic forms of infection are characterized by signs of respiratory distress including gasping and expectoration of bloody mucus with high morbidity and moderate-to-high mortality. Milder enzootic forms of infection are encountered increasingly in developed industries and manifest variously as mucoid tracheitis, sinusitis, conjunctivitis, general unthriftiness, and low mortality. Infected birds that recover often become latent carriers and may intermittently shed the virus into the environment and infect other birds. These recovered carrier birds are often the source of infection after introduction to naïve birds.1 GAHv-1 is a pathogen that is reportable in the state of Texas.
The chicken is the natural host for this virus although infections have been reported in pheasants, pheasant-chicken crosses, and peafowl. Rarely, the disease has been reported in turkeys and subclinical infections with seroconversion have been reported in ducks.1 How this virus was introduced into this backyard flock is unknown.
This case highlights the need to have ILT in rule-outs for acute upper respiratory disease in chickens. It also demonstrates the importance of biosecurity practices within backyard flocks similar to what is practiced by corporate commercial producers to protect these birds from accidental introduction of this disease.
To learn more about this case, contact Dr. Martin Ficken, Gonzales Resident Director. For more information about TVMDL and our test offerings, call 1.888.646.5623. To read other cases, visit our case study library.
Reference
1. Garcia M, Spatz S, and Guy JS. Infectious laryngotracheitis. In Diseases of Poultry, 13th edition, Swayne DE editor, pp. 161-179, Wiley & Sons, Inc., 2013.
Figure 1: Trachea. Extensive exudation of hemorrhage, fibrin, heterophils, macrophages, and sloughed epithelial cells into the tracheal lumen.
Figure 2: Trachea. Numerous intranuclear inclusion bodies in sloughed tracheal epithelial cells.