by Dr Oscar Blanco (DVM, PhD) Phibro Animal Health Central and Eastern Africa
Infectious Bronchitis (IB) Variant 2 (also known as IB variant IS/1494/06) was first detected in Zambia in 2017.
In an ongoing survey, Phibro has found it in two broiler flocks in the Lusaka province during the first half of 2022, confirming the problem is still prevalent. Since IB Variant 2 virus is sometimes difficult to detect, we estimate the prevalence in Zambia may be even higher. This article answers the most common questions on Variant 2 posed by our broiler customers and presents options to protect your farm. Remember to always consult your vet before modifying your vaccination plan.
What is a variant and why is it important to be aware of its presence?
A variant is a new strain of a given virus that, due to changes in very specific points of its genetic material, presents modifications in its structure and function. This results in changes in its virulence, in the type of disease it produces and, depending on the vaccination plan and vaccines used in the broiler flock, it might be able to escape immunity and infect vaccinated birds.
What should I expect to see if my broiler flock gets infected?
The symptoms and lesions depend on whether the broilers suffer an early or a late infection.
• In some cases of early infection, birds may not show any respiratory signs. The farmer only observes a reduction in performance and poor uniformity.
• When signs are present, they start around 10 to 14 days of age. The multiplication of Variant 2 in different tissues opens the door to secondary infections and septicaemia (general infection) verified at around 16 to 17 days of age. An increase in mortality (1 to 2% daily) is observed at around 20 days of age.
• If blood samples are taken at slaughter from a flock that has suffered an early infection, an increase in the antibody titres against Infectious Bronchitis is observed. It is, therefore, advisable to include serology just before slaughter as a routine procedure, particularly in large commercial enterprises.
• In post-mortem examination one may observe inflammation of the trachea (tracheitis), moderate to severe inflammation of the kidneys (nephritis) (Figure 1), general bacterial infections and polyserositis (Figure 2) (often times caused by E. coli or other coliforms), as well as lesions in the joints (such as femoral head necrosis).
• In flocks positive for Mycoplasmas, an infection with Variant 2 will result in reactivation of the dormant mycoplasma, aggravating the symptoms and prolonging the recovery.
The signs of late infection with Variant 2 in broilers begin at 28 to 30 days of age and often disappear a week later.
• The most striking feature is a sudden increase in mortality, between 2 and 5 % daily.
• Birds show lameness, with legs in wide stride position (as in Marek’s disease) or sitting on their legs and refusing to move (this is primarily due to pain caused by the severe kidney damage).
• The litter becomes wet, due to the kidney damage. The lesions in these organs reduce their ability of concentrating urine, resulting in an abnormal increase of water excretion.
• Once the symptoms subside, the surviving birds show delayed growth, resulting in poor flock uniformity.
• The post-mortem examination may show a wide range of lesions including inflammation of the kidneys (nephritis) (Figure 1) with accumulation of urates, inflammation of the trachea (tracheitis), inflammation of air sacs (airsacculitis) (Figure 3), secondary generalised infections (septicaemia, polyserositis) (Figure 2), inflammation of the intestines (enteritis), inflammation of the testicles (orchitis) (Figure 4), liver lesions, fluid collection around the heart (hydropericardium), swollen spleen, necrosis of the femoral heads, gout (accumulation of urates on the surface of organs).
• The occurrence of late septicaemia and polyserositis results in high levels of abattoir condemnations.
How do I protect my birds against infection with Variant 2?
As we mentioned in Issue 69 of ProAgri Zambia, maximum protection against Infectious Bronchitis Variant 2 is obtained with the application of a homologous vaccine, that is a vaccine containing a virus strain identical to the field virus. Currently, Phibro’s TAbic IB VAR206 is the only vaccine in the market containing a virus that is homologous to the circulating Variant 2 field strain. Additionally, Phibro’s TAbic IB VAR206 has also been shown to provide cross protection to some other field strains as well (such as 4/91, QX, etc). Heterologous vaccines (that is
vaccines containing a strain different from the field strain), used alone or in different combinations, confer variable, suboptimal levels of protection against the Variant 2 strain.
How often should I apply TAbic IB VAR206 in broilers?
High challenge risk situation:
In cases where Variant 2 has been a problem at the broiler farm or where it is present in the vicinity of the farm, protection is achieved with the application of Phibro’s TAbic IB VAR206 at the hatchery, followed by a second dose at 10 to 12 days at the farm. The application at the hatchery is essential to avoid the risk of early infections.
Medium challenge risk situation:
In cases where there is a potential risk of IB Variant 2 challenge in the area, Phibro TAbic IB VAR may be applied at the hatchery, followed by TAbic IB VAR206 10 to 12 days later at the farm. In all cases, TAbic IB VAR206 and TAbic IB VAR can be mixed with TAbic VH to also immunise the birds against Newcastle Disease.
Are there any ways of maximising the vaccination success?
• Apply the vaccines by coarse spray or eye drop only — not via drinking water. Fine spray is more effective but, under Zambian conditions, a coarse spray (150 to 200 micron) is recommended especially in young birds or in Mycoplasma positive flocks.
• Reconstitute the vaccine in clean, cool water with a pH of 7. It is very important to keep the water temperature between 6 and 10 °C during mixing and application. Studies have shown that the vaccine will be stable for up to 4 hours at 4 °C but at 19 °C you can lose a large proportion of virus immediately and it will be completely inactivated after 2 hours. Placing frozen ice bricks or ice packs in the container of the spraying machines may assist to maintain the temperature the closest to the ideal 4 °C.
• Use the correct volume of water — see the package insert for more information.
Please consult your veterinary advisor to get further information on IBV Variant 2 and how to control it at your enterprise.
Visit Phibro Academy (www. academy.pahc.com) to learn more about IB and other poultry topics.