Introduction

Since then, the disease has been a consistent and significant feature of poultry production throughout the world. Infectious bronchitis associated problems continue to be reported from all countries with a developed chicken industry. Although firm figures are not available, economic losses through respiratory disease in broilers and egg production/quality problems in layers continue to make this virus a potent limitation on good performance in those countries.

The virus has the knack of throwing up new serotypes or variants with irritating regularity, often keeping one step ahead of well tried vaccination strategies. With these variants has come an assortment of syndromes giving far more disease problems than the original "respiratory disease of baby chicks". In Europe, the recent variants 793/B (also known as CR88 or 4/91) and 42/96 have been particularly troublesome.

Clinical Signs: A. Broilers

The clinical signs seen are often related to the part of the chicken predominantly affected.

1. Respiratory tract
   Highly contagious respiratory disease causing gasping, sneezing, coughing, nasal discharge, variable head swelling, conjunctivitis and swollen sinuses. The damage to the upper respiratory tract allows rapid secondary bacterial, viral or mycoplasma infections resulting in the well established syndrome of chronic respiratory disease (CRD).
   
   

2. Intestinal tract
   As well as causing direct damage to the respiratory tract, more recent variants of IB appear able to depress weight gain and have an adverse effect on feed conversion ratio (FCR). This may be a reflection of morbidity due to respiratory disease or a direct effect on the intestinal tract causing diarrhoea and/or poor feed utilisation.
   
   

3. Kidney disease
   Certain IB strains, historically the Australian T strain, and more recently isolates from chickens in Belgium, Holland and France in the early 1990s, seem to target the kidneys leading to severe kidney damage, morbidity, dehydration and death.

B. Layers

1. Reproductive tract

   1. Laying hens
      Adverse effects on egg production with or without respiratory signs are seen regularly. This is usually followed by an increase in egg quality problems as soft shelled eggs, mis-shapes, roughened shells, loss of shell colour and poor quality albumen or "watery whites". Challenge in lay, especially approaching peak production, can cause severe economic effects and subsequently lead to mortality through egg peritonitis.

   2. Broiler breeders
      Egg production can be similarly adversely affected and shell defects may reduce hatchability.

   3. Young chicks
      Infection of young layers less than two weeks of age can lead to permanent damage to the developing reproductive tract. This may result in a failure of the oviduct to mature leaving the pullet as a "false" or "blind" layer or breeder.

   
   

2. Kidney damage
   Either as primary kidney disease or following a respiratory episode, kidney damage may lead to the deposition of urate crystals on internal organs rather than their normal excretion with the faeces. This is known as visceral gout. Alternatively, damage may cause kidney stones (urolithiasis) which can destroy one or both kidneys.

Diagnosis
Clinical signs and the effects on egg quality are strong pointers to diagnosing IB infection. This can be confirmed by blood testing (serology) for the classic or more recent specific variants. Virus growth and identification tests are helpful for added confirmation and the characterisation of new and emerging strains.

Disease Transmission
A HACCP approach to control of this economically important disease depends on knowing how the virus spreads. This is mainly via the respiratory tract from birds showing clinical respiratory disease. Infection is derived from inhalation of droplets containing the air borne virus which may travel several kilometres. Contaminated feed, drinking water and fomites, including human beings, probably contribute to more local spread.

The finding that certain strains have a tropism for the intestines or, at least, the ability to grow well in faecal material suggests that contaminated litter can be a potent method of spread of the virus from site to site. Also such viruses have the ability to persist on sites if cleansing and disinfection is not effective. Using an HACCP orientated programme (for example the Poultry Biosecurity Programme developed by DAHS) will cover all stages of control via cleaning and disinfection, using products independently proven effective against Infectious Bronchitis.

Egg transmission does not seem a significant route of spread but the fact that the virus has been isolated from semen indicates at least the theoretical possibility that infected cockerels may spread infection.

Control
The continuing economic impact of Infectious Bronchitis virus globally is an indication of the way that this ubiquitous virus seems able to "change its spots" and evade control programmes.

A well structured, comprehensive biosecurity strategy is the only hope of bringing about economic control, if not eradication. The DAHS Biosecurity Programmes mentioned above provide a step-by-step guide to hygiene and disinfection, incorporating HACCP methodology and identifying Critical Control Points.

Clearly, vaccination programmes will remain the cornerstone of this strategy, using a combination of live and inactivated vaccines targeted at the IB strains or variants active in a particular geographical area.

Management practices aimed at maintaining air quality over the birds and reducing challenges from E.coli, mycoplasma and viruses such as Infectious Laryngotracheitis (ILT) virus, avian pneumovirus (APV) and Newcastle Disease virus (NDV) will all reduce the economic impact of IB infection. Vaccination programmes to control these other viral challenges also have a place in the overall strategy.

Biosecurity Measures
This may be achieved in two important areas being terminal disinfection and ongoing biosecurity during the life of the flock.

a Terminal disinfection
A standard broiler programme incorporating disinfectants with proven efficacy against viral challenges, properly applied, can help to reduce the residual site contamination with all the contributing viruses.

Results of independent efficacy testing
	DAHS Longlife 250S	DAHS Farm Fluid S	DAHS Virkon S
Coronavirus spp.	1:600	1:100	1:100
Newcastle Disease virus (UK MAFF Approvals)	1:250	1:200	1:280

Spraying litter with DAHS Virkon S at 1:100 during dry cleaning reduces the likelihood of local spread of virus from contaminated litter.

A simple 5 step Terminal Disinfection Programme
Stage	Action	Suggested product used
1	Remove equipment and dry clean
2	Disinfect water system	Disinfectants (DAHS Virkon S)
3	Clean and sanitise buildings and equipment	Cleaner / Sanitiser (DAHS Biosolve DAHS DSC-1000)
4	Disinfect buildings, disinfect equipment and replace	Disinfectant (DAHS Longlife 250S, DAHS Hyperox, DAHS Farm Fluid S, DAHS Virkon S)
5	Fogging	Disinfectant (DAHS Virkon S)

b. Continuous Biosecurity

Important aspects are as follows:

• Limit people movement.
• Avoid visitors.
• Control site traffic to a minimum.
• Spray vehicles, especially wheels.
• Supply effective protective clothing.
• Provide boots.
• Use foot dips (with brush and hose).
• Hand washing facilities.
• Hand sanitisers.
• Water sanitisation.
• Aerial spray disinfection.

All these areas are important for controlling the effects of many infectious agents. In particular, with respiratory viruses such as Infectious Bronchitis, water sanitization seems to be especially important. The fact that the introduction of closed nipple water systems can have a potent beneficial effect on respiratory disease suggests that control of the E.coli burden into birds via the drinking water is a very important aspect. This can be supplemented and built upon by using in line water sanitisation during the life of the flock, with an effective product such as Virkon S.

Application	Dilution	Application Rate
Water Sanitation	DAHS Virkon S DAHS Virudine	1:1000 (Continuously) 1:2500 (Continuously)
Aerial Disinfection	Virkon S	1:200 (1 litre per 100 cubicmetres. Apply 2-4 times daily)

Conclusions

Infectious Bronchitis virus and the diseases it leads to will always be with us. New strains are likely to continue to emerge globally or in specific geographical areas with the ability to circumvent parts of the disease control programme, especially vaccination. Strict adherence to a biosecurity programme incorporating the strategic use of an effective cleansing and disinfection programme using products with a proven track record of efficacy and specificity offers the chance of control of the worst economic effects of this disease complex. When this is coupled with the strategic vaccination programme and an awareness of all the aspects of effective biosecurity, then significant viral diseases such as IB can be brought under practical and effective control.

Stephen A Lister BSc BVetMed CertPMP MRCVS is a partner in Crowshall Veterinary Services, a Norfolk, UK practice specialising in Poultry Consultancy and Diagnostic Services.

Further Reading

See Our Quick Poultry Disease Guide on Infectious Bronchitis

or Visit the Infectious Bronchitis (IB) information site

Source: DuPont Animal Health Solutions - August 2005