Avian Infectious Laryngotracheitis. Main challenges in poultry farming

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Servet (División de Grupo Asís Biomedia S.L.) Centro Empresarial El Trovador, planta 8, oficina I Plaza Antonio Beltrán Martínez, 1 • 50002 Zaragoza (España) Tel.: +34 976 461 480 • Fax: +34 976 423 000 • www.grupoasis.com

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Avian Infectious Laryngotracheitis Clara Marín Orenga Santiago Vega García

The publishing strength of Grupo AsĂ­s Editorial Servet, a division of Grupo AsĂ­s, has become one of the reference publishing companies in the veterinary sector worldwide. More than 15 years of experience in the publishing of contents about veterinary medicine guarantees the quality of its work. With a wide national and international distribution, the books in its catalogue are present in many different countries and have been translated into nine languages to date: English, French, Portuguese, German, Italian, Turkish, Japanese, Russian and Chinese.

Its identifying characteristic is a large multidisciplinary team formed by doctors and graduates in Veterinary Medicine and Fine Arts, and specialised designers with a great knowledge of the sector in which they work. Every book is subject to thorough technical and linguistic reviews and analyses, which allow the creation of works with a unique design and excellent contents.

Servet works with the most renowned national and international authors to include the topics most demanded by veterinary surgeons in its catalogue. In addition to its own works, Servet also prepares books for companies and the main multinational companies in the sector are among its clients.

MAIN CHALLENGES IN POULTRY FARMING

Avian Infectious Laryngotracheitis

MAIN CHALLENGES IN P

ULTRY FARMING

Avian Infectious Laryngotracheitis Clara Marín Orenga Santiago Vega García

AUTHORS: Clara Marín Orenga

Santiago Vega García.

FORMAT: 17 × 11 cm.

NUMBER OF PAGES: 62.

NUMBER OF FIGURES: 23.

BINDING: Paperback, wire-o.

RETAIL PRICE

30 €

Handbook entirely dedicated to avian infectious laryngotracheitis (ILT), based on a handy and visual approach of the topic. This handbook has been developed by prestigious, highly experienced and renowned authors, being experts in the area of avian diseases. An upto-date and complete review has been carried out including the most significant contents, such as aetiology, epidemiology, pathogenesis, clinical manifestations, etc. A chapter about vaccination has been properly developed in order to provide the main guidelines to avoid vaccination failures and control its prevalence and incidence.

Avian Infectious Laryngotracheitis

Presentation of the book Infectious laryngotracheitis (ILT) is a highly infectious respiratory disease caused by ILTV (Gallid herpesvirus 1), a highly contagious and economically significant avian herpesvirus.

Natural infections of ILTV are limited to galliform birds and cause an acute respiratory disease, which can be responsible for significant mortality and loss of productivity in the poultry industry, as many authors have stated before. ILT causes severe economic losses due to the decrease in egg production, weight loss, susceptibility to other respiratory infections, and high mortality and morbidity. Although diagnosis of severe acute ILT may be made on the basis of high mortality and expectoration of blood, the milder forms of the disease may resemble respiratory disease caused by other agents such as Newcastle disease and infectious bronchitis. Thus, for confirmation of diagnosis, laboratory methods are required. Those available are, as follows: histological examination of the trachea, detection of virus and detection of antibodies.

Generally speaking, in veterinary medicine, it is necessary to perform an updated and graphic review about it. To make it easier, the authors, some prestigious specialists in this field, have developed a thorough study in a didactic and visual way. The inclusion of images, tables, graphs and flowcharts focuses the reader’s attention on this topic. These graphic resources are accompanied by a short text to make the handbook understandable.

Thanks to this information, the veterinarians will get an overview of the disease and this tool will help them to know and tackle the disease successfully day after day.

Authors Clara Marín Orenga After graduating in Veterinary Science by the University CEU Cardenal Herrera in 2004, Dr. Marín Orenga earned a PhD by the same university in 2009. Since then, she has been a lecturer at the Veterinary Faculty of the University CEU Cardenal Herrera in Valencia (Spain).

Dr. Marín Orenga has participated in more than 18 investigation agreements with companies, associations and public organisms, which have resulted in publishing of 11 international papers (JRC), 25 national papers (general journals), 2 books, 1 patent, 14 lectures in transference journeys and 44 participations in international and national seminars. During this period she did investigation placements in the VLA (Veterinary Laboratories Agency) in Weybridge (United Kingdom), in the reference laboratory for animal health of the Ministry of Agriculture, Food and Environment of Spain and in the AHVLA (Animal Health and Veterinary Laboratories Agency) in Weybridge (United Kingdom). In January 2014, she was named European diplomate for poultry by the European College of Poultry Science.

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Avian Infectious Laryngotracheitis

Santiago Vega García PhD in Veterinary Medicine from the Complutense University of Madrid in 1999, diploma in health by the National School of Health Carlos III of Madrid in 1996, Master’s degree in management of centres and social and health projects in 2010 and Master’s degree in health and porcine production by the University of Lleida in 2011. He is currently the Dean of the Faculty of Veterinary Medicine of the University CEU Cardenal Herrera and member of the European and National Conference of Deans of the different degrees of health sciences.

He has focused his research in two well defined lines, on the one hand in virology, specifically in the virus of bovine viral diarrhea and Border disease, West Nile virus and avian pneumovirus. As second-line he has studied diseases related to public health, (leishmaniosis, leptospirosis, salmonellosis, campylobacteriosis and ehrlichiosis) and possible zoonoses such as hepatitis E. This productive activity has resulted in several research projects obtained in public competition, the direction of various Diplomas of Advanced Studies (DEAs), and doctoral theses. He has maintained an active participation in congresses and national and international conferences as well as publications in conference proceedings; he also published monographs, book chapters and scientific articles in national and international journals. He has participated in numerous courses on virology, organized by different institutions.

Communication services Website Online visualisation of the sample chapter.

Presentation brochure in PDF format.

Author´s CV. Sample chapter compatible with iPad.

www.grupoasis.com/promo/laryngotracheitis_avian

MAIN CHALLENGES IN P

ULTRY FARMING

Avian Infectious Laryngotracheitis Clara Marín Orenga Santiago Vega García

Table of contents 1. Introduction General definition Synonyms Economic significance History

6. Immunity 7. Diagnosis Diagnosis History and clinical signs Gross post-mortem lesions

2. Aetiology

Histological changes

The virus

Immunological techniques

Taxonomy

Antibody detection methods (serology)

Morphology

Antigen detection methods

3. Epidemiology Hosts Age distribution

Virus isolation in cell cultures Molecular techniques

8. Prevention and control

Geographic distribution

Control through vaccination

Transmission

Available vaccines

Incubation period

Hatchery vaccination

Incidence

Mechanism of protection

Mortality

Vaccination failure

4. Pathogenesis ILTV pathogenesis cycle

5. Clinical manifestations

Management control Biosecurity Cleaning and disinfection Genetic control

3

Epidemiology

Avian infectious laryngotracheitis

Hosts Domestic fowls and occasionally pheasants have been described as natural hosts for ILTV by several authors (Lee et al., 2015). However, some other avian species such as peafowls can sometimes be naturally infected by contact with chickens actively shedding ILTV. Starlings, sparrows, crows, doves, ducks, pigeons and guinea fowls appear to be refractory to ILTV. However, Yamada et al. (1980) reported subclinical infection and seroconversion in ducks and susceptibility of embryonated eggs of turkeys and chickens to ILTV. Moreover, duck eggs have been described as less susceptible, and eggs of guinea fowl and pigeons are not susceptible to the ILTV (Table 2).

12

Table 2. Hosts for ILTV.

Natural infection

Chicken

Pheasant

Peafowl

Starling

Sparrow

Duck

+

+/-

-

-

-

+/-

+ Susceptible +/- Less common but possible

Subclinical infection

+

+

-

-

-

+

Mortality

+

+

-

-

-

-

-

Resistant

EPIDEMIOLOGY

Age distribution Fowls of all ages are susceptible and, although greatest susceptibility occurs in very young chicks (Fig. 5), the disease is most commonly observed in the field in adult birds of about 3-9 months of age (Pattison et al., 2008). In endemic areas, older birds are frequently immune. Moreover, females are more resistant than males and light breeds are more resistant than heavier ones (Pattison et al., 2008). In recent years, ILT has also caused significant respiratory problems in broilers older than 3 weeks of age, especially during the cooler seasons of the year. This is believed to be due to unwanted spread of ILT vaccines between poultry flocks (Pattison et al., 2008).

13

Figure 5. Day-old chicks during first day of rearing.

3

Epidemiology

Avian infectious laryngotracheitis

Geographic distribution Since the identification of the disease in 1925, the virus has had a great impact on the poultry industry worldwide. However, morbidity and mortality rates vary depending on the virulence of the circulating strain. As reported by Menendez et al. in 2014 (Fig. 6), solely Greenland and Central America have been considered negative for ILT outbreaks.

Map regions shown in light purple indicate countries positive for ILTV between 2000 and 2013. Dark purple regions with a grid pattern indicate countries where ILT cases have been documented for longer than 10 years, while blue regions indicate countries that reported ILT outbreaks prior to, but not after 1999. Countries in yellow show that although no ILTV reports have been made, these countries are considered suspects due to their proximity to the ILTV affected countries.

14

EPIDEMIOLOGY

15 ILT + for 10 years or more ILT + between 2000-2013 ILT + in 1999 and prior ILT suspected ILT negative No data

Figure 6. Distribution of ILTV outbreaks worldwide (Menendez et al., 2014).

3

Epidemiology

Avian infectious laryngotracheitis

Transmission The primary host species for ILTV is the chicken, with natural transmission occurring by direct contact via the upper respiratory and ocular routes, mainly when infectious respiratory exudates are aerosolised or expectorated (blood and mucus) (Fig. 7).

No evidence exists for transmission of ILTV through the egg and newly hatched chicks (Pattison et al., 2008). However, in those birds that recover and even in birds given attenuated live vaccines, the virus can become latent, thereby turning these animals into carriers. The virus remains in latent form in the trigeminal ganglia (TRG) in the brain. Such birds, which usually show no signs of disease, may excrete the virus intermittently for long periods (Pattison et al., 2008).

16

Different sources of ILTV transmission have been described: Clinically affected chickens.

Chickens which are latent carriers of infection.

Fomites and poultry farm personnel contaminated with ILTV (Hidalgo, 2003).

EPIDEMIOLOGY

17

Figure 7.

Transmission of ILTV occurs mainly via respiratory and ocular routes. Image courtesy of MateoSantamaría, 2012.

3

Epidemiology

Avian infectious laryngotracheitis

Incubation period In the individual bird under commercial conditions, the clinical signs generally appear 6-12 days following natural exposure (Bagust et al., 2000). As is the case of other herpesviruses, ILTV establishes latent infections, which have been demonstrated by the re-isolation of the virus from the seventh week after infection by repeated tracheal swabbing and at 2 months after infection in tracheal organ cultures (Fig. 8) (Bagust, 1997).

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Figure 8. Tracheal swabbing.

EPIDEMIOLOGY

Incidence In areas of intensive production and large concentrations of poultry such as the United States, Europe, China, Southeast Asia and Australia, outbreaks of ILT are controlled using attenuated live vaccines produced by serial passages in embryonated hen eggs or tissue cultures. These vaccines are widely used in the poultry industry (Lee et al., 2015). For intensive broiler production, the short growth cycle and a high level of quarantine on sites can reduce the need for prophylactic vaccination. Within developed countries, ILT viruses have tended to persist as endemic infections within backyard and fancier chicken flocks (Bagust et al., 2000). Typically, outbreaks result in high morbidity (90 to 100 %) and variable mortality (5 to 70 %) rates, although the latter is usually around 10 to 20 % (Devlin et al., 2011).

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3

Epidemiology

Avian infectious laryngotracheitis

Mortality Severe epizootic forms of the disease cause high morbidity (90-100 %) and variable mortality rates; mortality can vary from 5-70 %, but is usually in the range of 10-20 % (Bagust et al., 2000).

Clinically, the disease may appear in three forms (Table 3), namely peracute, subacute, and chronic or mild. In the peracute form, the onset of the disease is sudden with a rapid spread. Morbidity is high and mortality may reach 100 % (OIE, 2014). In the subacute form, the onset of the disease is slower and respiratory signs may extend over some days before deaths are seen. Morbidity is high but mortality is lower than in the peracute form, and ranges between 10 and 30 %. A chronic or mild form may be seen in survivors of the peracute or acute forms of the disease, although some outbreaks themselves may be entirely mild. The morbidity and mortality rates of these strains are 5 % and around 2 %, respectively. The animals within chronic ILT flocks usually die of suffocation (Bagust, 2000).

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EPIDEMIOLOGY

Table 3. Morbidity and mortality rates of ILTV. Clinical form

Morbidity rates

Mortality rates

References

Peracute

High

>50 %

OIE 2014

Subacute

High

10-30 %

OIE 2014

Chronic/mild

5%

1-2 %

OIE 2014

21

4

Pathogenesis

Avian infectious laryngotracheitis

ILTV pathogenesis cycle The target organ system for ILTV infection and disease is the respiratory tract. The epithelium of the trachea and larynx is always affected, whilst other mucous membranes such as the conjunctiva, the sinus mucosa, air sacs and lung tissue may also become infected periodically. Whether chickens are exposed to ILTV by nasal, oral, conjunctival, or even experimental route such as via the intraorbital sinus, the most active replication of ILTV will occur within the tissues of the trachea (Fig. 9). Active viral replication occurs only during the first week after infection, although low levels of ILTV infectivity can be detected sporadically, up to ten days post infection (Bagust, 2000).

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Figure 9. ILT virus replicates actively within tracheal tissues. Image courtesy of Mateo-SantamarĂ­a, 2015.

5

Clinical manifestations Depending on the virulence of the ILTV strain, a peracute, acute or mild form of the disease can be seen in the field (Table 4). In the peracute form, birds may be found dead without prodromal signs, or they may show sudden acute dyspnoea with severe coughing and expectoration of mucus, bloodstained exudate and blood clots, followed by death within 1-3 days.

In the acute form, dyspnoea is a feature but it is not as severe as in the peracute form. In some cases, the increasing obstruction of the trachea with exudate causes the bird to breathe with long-drawn-out gasps, with a wide-open beak and often a high-pitched squawk, and invariably moist rales can be heard.

Avian infectious laryngotracheitis

Table 4. Summary of the main clinical manifestations of poultry laryngotracheitis, depending on the virulence of the ILTV strain.

Peracute form Dead No prodromal signs Severe dyspnoea

Acute form

Mild form

Long-drawn-out gasps

Slight coughing

Wide open beak

Head shaking

Dyspnoea

Nasal exudate

Moist rales

Moist rales

Decline in egg production

Decline in egg production

No decline in egg quality

No decline in egg quality

24

Conjunctivitis

CLINICAL MANIFESTATIONS

There may be nasal discharge and conjunctivitis with frothy exudate at the anterior canthus of the eye (Fig. 10). In the mild form, there may be one or more of the following signs: moist rales, slight coughing and head shaking, nasal exudate and conjunctivitis. Affected birds show depression commensurate with the severity of disease, and the most severely affected birds are recumbent on their hocks. Egg production is also affected and may cease entirely for a time but, in those birds that recover, egg production in uncomplicated cases returns to the expected level. There is no loss of egg quality (Pattison, 2008).

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Figure 10. Nasal discharge and conjunctivitis in a young chicken.

Image courtesy of BellĂŠs-Medall and BellĂŠs-Rubio, 2015.

6

Immunity

Avian infectious laryngotracheitis

A variety of responses are generated by the immune system following infection by ILTV, mainly humoral and cell-mediated (Palomino-Tapia, 2013). Best known are the virus-neutralising antibodies which become detectable in the serum within five to seven days of tracheal exposure, peak around twenty-one days, and then wane over the next several months to low levels at which they can persist for a year or more (Fig. 11).

Mucosal antibodies (immunoglobulin IgG and IgA) are capable of binding to the ILTV antigen, and low levels of virus-neutralising and enzyme-linked immunosorbent assay (ELISA) antibody activity. These antibodies become detectable in tracheal secretions and washings from approximately seven days postinfection, and plateau at days ten to twenty-eight (Fig. 12). However, numerous laboratory and field studies have independently confirmed that immune protection to ILTV challenge is neither indicated by, nor conferrable through the presence of serum or maternally-derived antibodies. Cell-mediated immunity is known to be the protective immune response in ILT infection and for vaccination. Studies

by Fahey and York, using vaccinated bursectomised chickens, have demonstrated that even tracheal mucosal antibodies are not essential in preventing the replication of virus in vaccinated chickens.

Rather, the effect of the mechanism of protection from ILT is likely to be the local cell-mediated immune response in the trachea (Bagust and Guy, 1997; Palomino-Tapia, 2013; OIE, 2014).

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IMMUNITY

Via respiratory tract

Peak

Detection

Decrease Lower detection

5-7 days

21 days

Figure 11. Description of virus-neutralising antibodies immunity against ILTV.

30 days 3 months

1 year

27

6

Immunity

Avian infectious laryngotracheitis

Peak

Detection

Decrease

28

7 days

Figure 12. Description of mucosal antibodies against ILTV.

10 days

28 days

7

Diagnosis

Avian infectious laryngotracheitis

Diagnosis

Thus, for confirmation of the diagnosis, laboratory methods are available (Table 5, OIE, 2014):

Diagnosis based on clinical signs and lesions in the peracute forms may be made on the basis of high mortality and expectoration of blood. However, mild forms of the disease may be difficult or impossible to differentiate clinically or at necropsy from other mild respiratory diseases such as Newcastle disease and infectious bronchitis.

a) Histological examination of the trachea b) Virus isolation c) Antibody detection d) Antigen detection

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Table 5. Test methods available for the diagnosis of avian infectious laryngotracheitis and their purpose (OIE, 2014).

Purpose Method

Population freedom from infection

Individual animal freedom from infection prior to movement

Contribution to eradication policies

Confirmation of clinical cases

Prevalence of infection– surveillance

Immune status in individual animals or populations post-vaccination

Agent identification1 Virus isolation Immunofluorescence for antigen ELISA–antigen detection PCR Histopathology

-

-

-

++

-

-

-

+

-

++

-

-

+

++

+

+++

+

-

++

+++

++

+++

++

-

-

-

-

++

-

-

Detection of immune response2 VN

+

-

+

-

-

+

ELISA–antibody detection

++

+

+++

+

+++

+++

Key: +++ = recommended method; ++ = suitable method; + = may be used in some situations, but cost, reliability and other factors severely limit its application; - = not appropriate for this purpose.

Although not all the tests listed as category +++ or ++ have undergone formal validation, their routine nature and the fact that they have been widely used without dubious results make them acceptable.

ELISA = enzyme-linked immunosorbent assay; PCR = polymerase chain reaction; VN = virus neutralisation.

1 A combination of agent identification methods applied on the same clinical sample is recommended.

2 One of the listed serological tests is sufficient.

31

The publishing strength of Grupo AsĂ­s Editorial Servet, a division of Grupo AsĂ­s, has become one of the reference publishing companies in the veterinary sector worldwide. More than 15 years of experience in the publishing of contents about veterinary medicine guarantees the quality of its work. With a wide national and international distribution, the books in its catalogue are present in many different countries and have been translated into nine languages to date: English, French, Portuguese, German, Italian, Turkish, Japanese, Russian and Chinese.

Its identifying characteristic is a large multidisciplinary team formed by doctors and graduates in Veterinary Medicine and Fine Arts, and specialised designers with a great knowledge of the sector in which they work. Every book is subject to thorough technical and linguistic reviews and analyses, which allow the creation of works with a unique design and excellent contents.

Servet works with the most renowned national and international authors to include the topics most demanded by veterinary surgeons in its catalogue. In addition to its own works, Servet also prepares books for companies and the main multinational companies in the sector are among its clients.

PRESENTATION BROCHURE MAIN CHALLENGES IN P

Servet (División de Grupo Asís Biomedia S.L.) Centro Empresarial El Trovador, planta 8, oficina I Plaza Antonio Beltrán Martínez, 1 • 50002 Zaragoza (España) Tel.: +34 976 461 480 • Fax: +34 976 423 000 • www.grupoasis.com

ULTRY FARMING

Avian Infectious Laryngotracheitis Clara Marín Orenga Santiago Vega García