Omony John Bosco, Wanyana Agnes, Mugimba Kizito K, Kirunda Halid, Nakavuma Jessica Lukanga, Otim-Onapa Maxwell, Byarugaba Denis Karuhize
College of Veterinary Medicine, Makerere University, P.O. Box 7062, Kampala, Uganda.
Uganda Industrial Research Institute (UIRI), P.O. Box 7086, Kampala, Uganda.
Virol J. 2016 Jun 21;13:103. doi: 10.1186/s12985-016-0560-0.
Uganda poultry production is still faced with frequent outbreaks of Newcastle disease (ND) in the backyard free-range systems despite the accessibility of cross protective vaccines. Live bird markets and waterfowl has long been reported as a major source of disease spread as well as potential sources of avirulent strains that may mutate to virulent strains. ND-virus has been reported enzootic in Ugandan poultry but limited studies have been conducted to ascertain thermostability phenotypes of the Ugandan ND-virus strains and to understand how these relate to vaccine strains.
This study evaluated thermostability of 168 ND-virus field isolates recovered from live bird markets and waterfowls in Uganda compared to two live commercial vaccine strains (I2 and LaSota) by standard thermostability procedures and Hemagglutinin-Neuraminidase (HN) gene domains. The known pathotypes with thermostability profiles were compared at HN amino acid sequences.
Field isolates displayed disparate heat stability and HN gene domains. Thermolabile isolates were inactivated within 15 min, while the most thermostable isolates were inactivated in 120 min. Four thermostable isolates had more than 2 log2 heamaglutinin (HA) titers during heat treatment and the infectivity of 9.8 geometric mean of log10 EID50 % in embryonated eggs. One isolate from this study exhibited a comparable thermostability and stable infectivity titers after serial passages, to that of reference commercial vaccine was recommended for immunogenicity and protection studies.
The occurrence of ND-virus strains in waterfowl and live bird markets with disparate thermostability and varying HN gene domains indicate circulation of different thermostable and thermolabile ND-virus pathotypes in the country.
尽管有交叉保护疫苗，但乌干达的家禽生产在后院自由放养系统中仍频繁爆发新城疫（ND）。长期以来，活禽市场和水禽一直被报道为疾病传播的主要来源以及可能突变为强毒株的无毒株的潜在来源。据报道，ND病毒在乌干达家禽中呈地方流行，但为确定乌干达ND病毒株的热稳定性表型以及了解这些表型与疫苗株的关系所开展的研究有限。
本研究通过标准热稳定性程序和血凝素-神经氨酸酶（HN）基因结构域，评估了从乌干达活禽市场和水禽中分离出的168株ND病毒野毒株与两种市售活疫苗株（I2和LaSota）相比的热稳定性。在HN氨基酸序列上比较了具有热稳定性特征的已知致病型。
野毒株表现出不同的热稳定性和HN基因结构域。热不稳定毒株在15分钟内失活，而最耐热的毒株在120分钟内失活。4株耐热毒株在热处理期间血凝素（HA）滴度增加超过2 log2，并且在鸡胚中的感染性为9.8 log10 EID50%的几何平均数。本研究中的一株毒株在连续传代后表现出与参考市售疫苗相当的热稳定性和稳定的感染性滴度，建议用于免疫原性和保护性研究。
水禽和活禽市场中存在热稳定性不同且HN基因结构域各异的ND病毒株，这表明该国存在不同的耐热和热不稳定ND病毒致病型在传播。
