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Emerging Trends in Veterinary Virology

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Infectious Laryngotracheitis Virus: Molecular Biology, Pathobiology, and Control Strategies

Author(s): Muhammad A. Shahid*, Ahmad J. Sabir, Muhammad I. Arshad, Sadeeq ur Rahman, Muhammad F. Tahir, Muhammad N. Zahid and Muhammad A. Zahoor

Pp: 18-40 (23)

DOI: 10.2174/9789815036961122010004

* (Excluding Mailing and Handling)

Abstract

Infectious laryngotracheitis (ILT) is an economically important respiratory
disease of chickens that is prevalent throughout the world. It is caused by an infectious
laryngotracheitis virus (ILTV), also named Gallid alphaherpesvirus 1 (GaHV-1). It is a
member of the genus Iltovirus, subfamily Alphaherpesvirinae, family Herpesviridae
and order Herpesvirales. The ILTV genome is a linear double-stranded DNA molecule
with an average genome length of 151,607 nt. Twelve herpes simplex virus -1
homologue genes have been identified in the ILTV genome, with seven of them,
glycoproteins B, C, H, K, L, M and N, present in the UL region, while glycoproteins D,
E, G, I and J are present in the US region of the ILTV genome. Although chicken is the
natural host of ILTV, infections have also been reported in pheasants, pheasant-chicken
crosses, peafowls, turkeys, and ducks. An incubation period of 3–12 days is followed
by an acute phase of the infection which lasts 1–2 weeks. During this phase, the virus
replication occurs in the conjunctiva, trachea, and larynx, resulting in conjunctivitis,
gasping, coughing, and expectoration of blood-mixed mucus. ILTV infection results in
decreased weight gain and egg production. It causes 0 to 80% mortality depending on
the virulence of the strain involved. Like other herpesviruses, ILTV establishes latent
infection in trigeminal ganglia and virus reactivation and shedding occur following
various stress factors.
ILTV infections are generally diagnosed by the typical clinical signs and detection of
intranuclear inclusion bodies in the affected tissues. Furthermore, the detection of
virus-specific antigen by fluorescent antibody, immunohistochemical staining of
smears and tissues, detection of DNA by a polymerase chain reaction, and virus
isolation by inoculating embryonated chicken eggs or cell cultures can also be
performed. Virus neutralization assays and different types of ELISAs have also been
established. To control ILTV infections, a combined effort is required encompassing
prompt disease diagnosis, the use of geographic information system technology,
biosecurity, vaccination, differentiation of infected from vaccinated (DIVA), and
eradication of reservoir hosts.

Keywords: Alphaherpesvirinae, Coughing, Expectoration of blood, GaHV-1, Gallid alphaherpesvirus 1, Gasping, Herpesviridae, Herpesvirales, Infectious laryngotracheitis (ILT), Infectious laryngotracheitis virus (ILTV), Iltovirus, Respiratory disease.

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