Infectious laryngotracheitis - poultry

Infectious laryngotracheitis (ILT) is an economically important respiratory disease of poultry. This highly contagious disease is caused by Gallid alpha herpesvirus type 1 (GaHV-1), commonly known as infectious laryngotracheitis virus (ILTV). The virus can be easily transmitted by infected birds and fomites. Lax biosecurity, transportation of infected birds, and spread of contaminated litter facilitates spread of the virus. Clinical signs of respiratory disease are not pathognomonic. Diagnosis is by real-time PCR and histopathology . Implementation of biosecurity is necessary for prevention, but vaccination is commonly used for control of the disease in endemic regions worldwide.

1. INFECTIOUS LARYNGOTRACHEITIS AVIAN DIPTHERIA RANJINI MANUEL

2. INTRODUCTION Viral respiratory tract infection of chicken -also affect pheasants and peafowl P roduces severe production losses mortality of infected birds decreased weight gain and egg production. The principal lesion is tracheitis In infected birds, the virus can become latent and re-excreted at a later date without clinical signs

3. history The disease was first reported in 1925 in Canada , followed by the USA in 1926, Australia and Great Britain in 1935, and Europe in 1940 (Cover, 1996). By 1962 the disease had been described in at least 40 countries ( Pulsford , 1963). Gibbs described brush vent application as the first vaccination method for ILT (Gibbs, 1933, 1934 ). Live virulent virus isolated from tracheal scraping preparations was used for this. Response of birds to the vaccine involved inflammation of the cloacal mucosa 3 to 8 days post vaccination (Gibbs 1933, 1934). Although vaccination provided birds with protection against disease , immunity was not achieved and vent-vaccinated birds were still able to shed live virulent virus

4. HISTORY Described in many countries- of intensive production and large concentrations of chickens North America, South America, Europe, China, Southeast Asia and Australia outbreaks continue to occur- when ILT virus strains- contact from persistently infected flocks to non-vaccinated birds Field strains and live attenuated vaccine- establish the latent infection

5. ETIOLOGY Family - Herpesviridae S ub family - alpha Herpesvirinae currently depicted as gallid herpes virus 1 LTV glycoproteins gB , gC , gD , gX , gK The target organ of virus is upper respiratory tract ,conjunctiva Survive outside the host- weeks – longer in cold- presence of organic matter

6. Etiology Strain Differentiation S trains are homogenous – serum neutralization, IF and ELISA tests Differentiation done by – restriction endonuclease analysis of DNA, PCR, RFLP and Morphology in cell cultures .

7. Host factors Only domestic fowl and occasionally pheasants All ages are susceptible -  very young (3-9 months ) Endemic area older will be immune Males > females Heavier > light Exacerbated by concurrent infection with ND, IB, Fowl Pox, Haemophilus gallinarum and Mycopasma Deficiency of vit A  ammonia increases the severity

8. epidemiology

9. TRANSMISSION Transmitted through aeroso l or expectorant from infected birds It enters the body through upper respiratory tract and conjunctiva Transmission through egg is not known to occur Shed mainly in exudates from Nares Oropharynx Trachea conjunctiva

10. Among recovered birds ,even birds vaccinated with live vaccines can become latent the birds which appears apparently healthy could act as carriers and excrete virus intermittently for years Latency seen in trigeminal ganglia Viable in fomites for weeks Mechanical transmission – personnel, wild birds, cats and dogs

11. Precipitating factors Movement of stock Handling social stress Onset of lay

12. pathogenesis Virus attaches to the receptor Envelop fusion into the host cell Nucleocapsid released to the cytoplasm releases viral DNA into the nucleus Transcription & replication of DNA Monomeric units & packaged to nucleocapsid Acquire envelop by migration through inner lamellae of N.M Exit endoplasmic reticulum Accumulate in vacuoles in cytoplasm Virions released by cell lysis

13. Clinical signs Period of incubation is 6 – 12 days ,it can be 14 days in chronic carriers The disease are manifested in three form Per acute form Subacute form Chronic form

14. Per acute form The bird appears dead with out showing any prodromal signs shows sudden dyspnea with severe coughing expectoration of mucous and blood stained exudate Clots of blood may be coughed up and can be found on the floor and walls D eath in 1 to 2 days Post-mortem changes are confined to the upper respiratory tract hemorrhagic tracheitis with blood clots, mucoid rhinitis blood-stained mucus along the length of the trachea. Morbidity is very high and mortality may exceed 50%

15. Sub acute form dyspnea, gasping with wide open beaks High pitched squawk- moist rales The onset of illness is slower and respiratory signs may extend over some days before deaths are seen. The morbidity is high but the mortality is lower , between 10% and 30%. Post-mortem findings are less severe -consist of mucoid exudate with or without blood in the trachea . Yellow caseous diphtheritic membranes may be found adherent to the larynx and upper tracheal mucosa

16. Birds extend their head and neck to facilitate breathing (commonly referred to as “pump handle respiration ”)

17. Usually the first symptom noticed will be watery eyes

18. Chronic form Recovered birds Incidence of chronic ILT within a flock may be only 1–2 % Signs include coughing and gasping, with nasal and oral discharge and reduced egg production. On post-mortem examination, diptheritic and caseous necrotic plaques and plugs are found in the trachea, larynx and mouth Recovered carrier birds are also a potential means of transmission of the disease

19. Virus detection/isolation Infectious laryngotracheitis virus can be grown in fertile chicken eggs and several avian primary cell cultures Epithelial scraping and tracheal swab- emulsified in nutrient broth and supernatant- inoculated in CAM Inoculation- CAM of eggs after incubation for 10- 12 days results in pock formation and embryo death between 2- 12 days post inoculation .

20. The virus can be propagated in avian cell cultures derived from Chick embryo (liver, lung, kidney and tissues) where the typical cytopathic effect is syncytium formation ( cow dry type A intranuclear inclusion bodies ) As it is surrounded by a halo with migration of the chromatin –difficult to demonstrate – pathognomonic to ILT Epithelial hyperplasia – multinucleated cells – includes in the hemorrhage of lamina propria Desquamation of mucus glands Regeneration occurs – 6days- after no longer IB will be seen IB can be stained by giemsa / hematoxylin & eosin

21. Chick embryo liver has been found to be the most sensitive The target organs for ILTV infection -respiratory tract epithelium of the trachea and larynx. Other mucous membranes such as the conjunctiva, as well as respiratory sinuses, air sacs and lung tissue can be used 4-6 hrs post inoculation - syncytium formation. IB -12hr post inoculation as multinucleated giant cells

22. Virus identification Can be done by virus neutralization – time consuming Electron microscopy AGID – commonly used Immunofluoresence and immune peroxidase test- rapid tests (tracheal sections ) Antigen capture ELISA – accurate method DNA hybridization PCR- within 2 days, sensitive ELISA – large flock – semi automated commercial kits available

23. Immune Responses Virus neutralization antibodies – detected within 5-7days and peaks at 21 days. Antibodies waned to be detected to low level over a year ILTV vaccinated chicks – IgA and IgG synthesizing cells in trachea by day 3 P.I IgA provide resistance to mucosal surface Maternal antibodies to ILTV do not protect offspring or interfere with vaccination

24. Latency of ILTV Trigeminal ganglion – site of latency It provide main sensory innervation to tissues of URT Reactivation of latent ILTV from TRG in 15 months after vaccination- reported ( Kaleta et al., 1986) Stress, rehousing etc can also potentially reactivate the virus

25. Chemical & physical resistance  infectivity by organic solvents- chloroform and ether Retain infectivity when kept in glycerol/ nutrient broth @ 4 degrees Rapidly inactivated by heat @ 55 degrees for 15 mins or 38 degrees for 48 hrs LTV survive tracheal exudate and chicken carcass for period of 10-100days @13-23 degrees Inactivated < 1 min under 3% cresol Decontamination- iodophores – halogen detergent Complete inactivation – 5% hydrogen peroxidase as a fumigant in poultry houses

26. control The application of biosecurity measures will avoid exposing susceptible chickens via contaminated fomites For control of an ILT outbreak, the most effective approach is a coordinated effort to obtain a rapid diagnosis , to establish a vaccination program, and prevent further virus spread There should not be mixing of the flock Once a flock is affected – cull After fumigation and disinfection take new disease free flock

27. ILT Vaccination Vaccination is done with either ; 1. Live attenuated vaccines 2 . Viral vector recombinant vaccines 3. Modified live vaccine

28. ILT Vaccination Live Vaccines In the 1950s and 1960s - attenuate field strains by consecutive passages in chicken embryos. These vaccines exhibited reduced levels of virulence, increased safety, and improved efficacy. It is now applied as eye drop or through mass vaccination by water or spray

29. In 1964 the first tissue culture (TCO) modified vaccine was developed ( Gelenczei & Marty, 1964); its attenuation was obtained by consecutive passages of the virulent ASLL-6 strain in primary tissue cultures of chicken cells.

30. ILT - Viral Vector Recombinant Vaccines There are many reported experiments on the use of Fowlpox virus and Marek's disease virus as vectors for the insertion of genes from avian pathogens ILTV genes have also been inserted into these vectors, for this either the ILTV glycoprotein B or glycoprotein D genes (Keeler  et al ., 1992 ). The recombinant viruses produce proteins, which are immunogenic and elicit a protective immune response. They are increasingly safe due to their inability to transmit from bird to bird, revert to virulence, establish latent infections, or recombine. In addition, they can be administered in ovo without a negative impact on production performance (Johnson et al., 2010)

31. ILT Vaccination At present, only modified-live vaccine viruses are available for prophylactic vaccination . Modified live virus vaccines are prepared by propagation of vaccine strains in either : 1. Cell culture (tissue culture-origin) • Low post vaccine reaction, suitable for priming dose . 2. Embryonated eggs ( chick embryo-origin) • High post vaccine reaction, suitable for booster dose (Guy & Garcia, 2008)

32. ILT Vaccination Primary Vaccination Primary vaccination with current modified-live ILT vaccine strains will confer: Partial protection against challenge by 3-4 days post exposure. Complete protection after one week. High levels of protection occur between 15-20 weeks post vaccination, with variable degrees of protection within a flock over the following year.

33. CONTROL Quarantine vaccination, if enzootic or epizootic in an area, after 4 weeks of age. All-in/all-out operation. Keep susceptible stock separate from vaccinated or recovered birds. Apply strict biosecurity in moving equipment or materials between these these categories of stock.