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Is Infectious Bronchitis Variant 2 (IS/1494/06) a problem at your layer farm?

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by Dr Oscar Blanco (DVM, PhD), Phibro Animal Health Corporation, Central and Eastern Africa

In issue 69 of ProAgri Zambia, we presented an overview of the signs and lesions of infectious bronchitis Variant 2 (also known as IS/1494/06) in broilers, layer hens and breeders. This variant was first reported in Zambia in 2017, and Phibro has detected it again in 2022, confirming its circulation in the country.

In this new article, we give information that may assist you to detect the problem at your layer enterprise. Please consult your veterinarian to get a professional diagnosis, and to obtain guidance on how to protect your birds against IB Variant 2.

What do you see in layer birds?

In cases of early infection:

If the infection with IB Variant 2 occurs during the pullet phase, there will be permanent damage in the reproductive tract. In cases when the virus infects the birds in the first or second week of age, birds may develop silent layer syndrome. In this case, birds reach sexual maturity and, most of the times, they look like normal adult hens, however they do not produce eggs.

Figure 1: Reproductive tract of the hen. (After Jonchere et al, 2010)

Although the ovary is functional and ovulation is verified, the oviduct (Figure 1) will develop cysts in its wall (Figure 2), preventing the progression of the yolk along the oviduct, resulting in failure to produce eggs. In a few cases, when cysts are very large, the abdomen appears distended and the birds adopt a penguin-like vertical position (Figure 2), waddling when walking. If the birds are in cages, the ones with distended abdomens normally choose to stay at the back of the cage. The egg yolks are released inside the abdomen and reabsorbed, although peritonitis (inflammation and infection in the abdomen) can sometimes develop.

Figure 2: Silent later syndrome. A, B and C: Cystic oviduct (CO). D: Penguin posture.

It is difficult to detect false layers, as most of the time they do not show any signs suggesting disease. They are normally found when inspecting the flock due to unusual production curves, for example in flocks where there is a delay to reach peak and/or the maximum production is considerably lower than the production target.

When layers get infected:

Changes in egg production

Although layers can be infected at any age, infection often occurs during the peak of lay. Infected flocks show a drop in production sometimes as large as 50%. Usually, egg production recovers in approximately 3 to 4 weeks, however it stabilises at levels lower than before the outbreak. That being said, some flocks do not show production drops. If birds are not vaccinated after the outbreak, using the correct vaccine at the right time, the problem will return every 6 to 12 weeks; this normally results in oscillations of egg production, mostly accompanied by changes in egg quality.

Changes in egg quality

The virus affects different sections of the oviduct (Figure 1), resulting in a range of changes in egg quality:

Lesions in the magnum:
The magnum (Figure 1) is the section of the oviduct that secretes the egg albumin. The inflammation of its wall results in eggs with very liquid albumin, or an albumin that liquifies within a couple of minutes after cracking the egg open.

Lesions in the uterus

The uterus (Figure 1) is the organ where the shell is formed and the external cuticle, responsible for the egg colour, is deposited.

IB lesions in the uterus initially cause eggs to lose their shine and their traditional golden colour (Figure 3). This translates into a range of different tones of brown when inspecting egg trays after collection (Figure 3). The discolouration may eventually lead to completely white shells (Figure 3).

Figure 3: Eggshell alterations due to IB Variant 2. A: Normal; B: Discoloured eggs; C and H: Discoloured shells with calcium deposits; D and J: Soft shell eggs; E, F, and G: Misshapen eggs; I: White, brittle shell; K: Egg tray showing variations in colour and shape.

When the virus affects the uterine glands in charge of producing calcium carbonate, the shells become thinner, brittle, chalky, deformed, or even soft (when the mineralisation is totally absent) (Figure 3). Sometimes, eggs are laid with irregular deposits of calcium on their surface (Figure 3).

As mentioned above, if birds are not vaccinated with the correct vaccine and at the right times, the problems with egg quality and production will return in 6 to 12 weeks.

Other signs and lesions observed

Infected layers can present mild respiratory problems, concurrent with inflammation of kidneys (nephritis), and diarrhoea. When the damage in the kidneys is severe, urates start to accumulate first in the kidneys (Figure 4) and then in other internal organs, a condition known as gout (Figure 4). Daily mortality can sometimes be as high as 2%.

Figure 4: A. Nephritis (kidney inflammation); B. Urate accumulation on liver surface (gout).

The impact on the flock’s performance can be intensified by the occurrence of secondary infections, especially in flocks infected by mycoplasmas. These birds show generalised infections (septicaemia, polyserositis), and airsacculitis (inflammation of air sacs). This translates into long-haul respiratory symptoms, higher mortality, and low productive performance.

How to prevent infection with Variant 2?

As we mentioned in our article in ProAgri 69, Phibro IB VAR206 is the only vaccine that will give the highest protection against Variant 2, since it contains a virus that is the closest possible to the field strain. The optimum protection is achieved after priming the birds with two doses of the vaccine administered 10 to 14 days apart, followed by boosters at 10 to 12 weeks, just before transfer, and every 8 weeks in lay (Table 2).

The vaccine should be applied by coarse spray, or by eye drop, as levels of protection achieved with vaccination in drinking water are very poor. In order to protect against early Variant 2 infection and avoid the silent layer syndrome, birds should be spray vaccinated with Phibro IB VAR206 at day 1 at the hatchery, followed by a second spray vaccination at the farm at day 10. The vaccine can be sprayed together with Phibro VH against Newcastle disease.

Please visit Phibro Academy (www.academy.pahc.com), register, and access further information on IBV variants and other poultry topics via their range of online webinars.

The post Is Infectious Bronchitis Variant 2 (IS/1494/06) a problem at your layer farm? appeared first on ProAgri.


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