Global change in vaccination practices


D and IB are caused by a paramyxovirus and coro- navirus, respectively. Notably, mortality of 80- 100% and 25-80% have been reported for ND and IB, respectively. To date, there are no specific glob-

al figures outlining total economic losses due to ND and IB. However, a recent publication, the World Livestock Disease At- las (The World Bank, Agriculture and Rural Development), stated that losses in poultry production due to IB are far high- er than losses due to ND. Workers in Brazil indicated that for every 1,000 chicks placed, losses due to IB in broiler and breeder chickens were estimated at US$ 266 and around US$ 3,567, respectively.

Vaccination against ND and IB Traditionally, for many decades live ND or IB vaccines were administered to chicks when maternally derived antibodies (MDA) against ND or IB had sufficiently declined. This was practiced because highly virulent live vaccines had been shown to neutralise MDA and potentially cause disease in susceptible flocks. However, with the development of attenu- ated live vaccines continually improving, less virulent vac- cines were administered at a day-old. This therefore induced early immunity and reduced the frequency of vaccine admin- istration to the same flock (thus avoiding stress to birds). Vac- cination at a day-old also means that the vaccines are admin- istered at the hatchery which provides a cleaner and more regulated vaccination environment compared to the farm. Initially, only live ND vaccines were applied in day-old broiler chicks at the hatchery or farm in many countries. With the availability of milder IB vaccine strains such as H120 or Ma5, producers started to use a combined IBMass+ND vaccination. This has been the practice for a few decades now and is still common in many countries. From the 1990s, poultry farming began experiencing the emergence of variant IBVs (such as 793B, QX, Q1, Variant 2), which caused increased levels of res- piratory and kidney disease in broilers, with high mortality and carcass condemnation at abattoirs. To tackle this, in addi- tion to IBMass+ND at a day-old, a second dose of IBMass or IBVariant given at 10-14 days became common practice. Un- fortunately, in some countries such vaccination regimes did not manage to suppress the production losses effectively. Our

In global chicken farming, other than avian influenza, Newcastle disease (ND) and infectious bronchitis (IB) are considered the most economically important diseases. According to evidence-based publications and survey results, global vaccination practice of day- old broiler chicks has been shifting from IBMass+ND to co-vaccination with IBMass+IBVariant+ND.

research at the University of Liverpool has shown that IB- Mass+IBVariant or IBMass+IBVariant+ND can be jointly ad- ministered in day-old broiler chicks. Such a vaccination re- gime provided excellent protection (>90%) against classical and variant IBV strains, including M41, 793B and QX (Table 1). In addition, ND HI titres were equal to or more than 5 log2, which is considered to be a protective titre. In particular, the compatibility of administering IBMass+IBVariant+ND in day- old commercial broiler chicks has given producers much more confidence where ND is endemic. Co-vaccination in- duced the same protection against challenge as if the vaccines had been administered separately.

From IBMass+ND to IBMass+IBVariant+ND To ascertain the degree of change in ND and IB vaccination programmes since 2012, a short survey was undertaken in different regions of the world. Producers in Africa, Asia, Europe and South America, whose combined production amounts to approximately 1,337 million chickens, were sur- veyed. From the information they provided, it was evident

Table 1 – Ciliostasis protection scores for IBV vac- cination schemes following challenge by classical and variant IBV strains. University of Liverpool.

Vaccination Scheme IBMass

IBMass+IBVariant IBMass+ND IBMass+IBVariant+ND

IBV Challenge strain M41 M41 793B QX

M41 M41

Ciliostasis score (%) 95

90-99 93 92 95

94-97 ▶ POULTRY WORLD | No. 1, 2021 25

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