Development of an improved (DIVA) vaccine against peste des petits ruminants and technology for a control strategy in endemic areas

通过开展协调一致的大规模疫苗接种运动，我们在防治许多病毒性疾病方面取得了很大进展。一种病毒性疾病(天花)已被根除，其他人类疾病(脊髓灰质炎、麻疹)接近根除或大幅下降。在牲畜疾病方面，牛瘟这一历史上最大的牲畜杀手之一已基本根除，该方案已进入最后确认阶段。然而，作为牛瘟病毒的近亲，小反刍动物害虫病毒(PPRV)是一个日益严重的问题，它从撒哈拉以南非洲相对有限的地区向北和向南传播，从印度传播到西藏和东南亚其他国家。这种病毒在绵羊和山羊中引起一种严重的疾病，因此对发展中国家最贫穷的牧民和小农所拥有的主要牲畜类型构成威胁。这种疾病的传播可能部分是由于牲畜贸易(流动)的增加，随着各国被确认为没有牛瘟，这种贸易成为可能。现有的针对PPR的疫苗正被用来试图在特定地区控制疾病。这些疫苗基本上是普通病毒的弱化版本，提供终身免疫力，但它们有两个主要缺陷：(I)它们不耐热，因此它们需要所谓的“冷链”，即具有稳定冷藏电源的兽医网络，以及配备冷库的车辆来分发疫苗；(Ii)无法区分接种疫苗的动物和那些感染了疾病并康复的动物。因此，一旦疫苗接种活动正在进行，就不可能检测到动物以前是否被感染，或者被感染的动物是否被带到正在进行疫苗接种的地区。该项目的主要目的是生产一种克服这些问题的疫苗。我们将制造一种名为鸡痘病毒(FPV)的禽类病毒的重组版本，这是一种天然耐热的病毒。FPV不会在哺乳动物细胞中复制，因此重组体不会在绵羊/山羊中引起疾病。此外，工作中使用的FPV毒株是一种用于预防鸡痘疾病的疫苗，因此家禽也不存在风险。这些重组的FPV在注射到绵羊体内时会表达两种PPRV蛋白，对这些蛋白的免疫反应应该会保护绵羊免受PPRV的攻击；然而，由于并不是所有的PPRV蛋白都是制造出来的，所以这套免疫反应将不会与真正的PPRV感染时看到的一样，因此将有可能确定哪些动物已经接种了疫苗，哪些动物受到了感染。为了增强对重组FPV蛋白的免疫应答，我们还将加入其他表达绵羊免疫刺激蛋白的重组FPV。我们希望这将意味着单剂新疫苗就足以保护动物，从而降低疫苗接种成本。我们将在英国研究所的绵羊或山羊身上测试新疫苗，然后在乌干达农场的更多动物身上进一步测试，乌干达目前正在发生PPR疫情。这将确保当动物属于发展中国家发现的类型并在相同条件下饲养时，仍然可以看到免受感染的保护措施。乌干达的其他任务是测试和验证一种新的诊断测试，它将只检测PPRV感染，而不是疫苗接种，以及一种“怀孕测试”式的设备，它将能够直接从动物泪液样本中诊断PPR疾病，而不需要实验室(所谓的“Penside”测试)。这项检测将极大地简化在PPR病毒尚未确立的地区检查感染情况。

We are making great progress in the fight against many viral diseases through the use of concerted mass vaccination campaigns. One viral disease (smallpox) has been eradicated, and other human diseases (polio, measles) are close to eradication or in great decline. In the area of livestock disease, one of the great historical killers of cattle, rinderpest, has been essentially eradicated, a programme that is in the last stages of confirmation. However, a close relative of rinderpest virus, peste des petits ruminants virus (PPRV) is a growing problem, spreading from a relatively limited area of sub-Saharan Africa both northwards and southwards, and from India into Tibet and other countries in South-East Asia. This virus causes a serious disease in sheep and goats, and is thus a threat to the primary types of livestock held by the poorest herders and small holders in the developing world. It is possible that the spread of this disease may in part be due to the increased trade in (movement of) livestock which became possible as countries became confirmed as free from rinderpest. There are existing vaccines against PPR which are being used to try to control the disease in specific areas. These vaccines are essentially weakened versions of the normal virus, and give life-long immunity, but they have two major faults: (i) they are not heat stable, so they require a so-called 'cold chain', a network of veterinarians with stable power supplies for refrigerated storage, and cold-store-equipped vehicles to distribute the vaccine; (ii) there is no way to differentiate vaccinated animals from those that have had the disease and recovered. Therefore, once a vaccination campaign is under way, it becomes impossible to detect whether animals have been infected previously, or whether infected animals have been brought into an area where vaccination is being carried out. This project is primarily aimed at producing a vaccine which overcomes these problems. We will make recombinant versions of an avian virus called fowlpox virus (FPV), a virus which is naturally heat tolerant. FPV does not replicate in mammalian cells, so the recombinants cannot cause disease in the sheep/goats. In addition, the strain of FPV used for the work is one used as a vaccine against fowlpox disease in chickens, so domestic fowl are also not at risk. These recombinant FPV will express two PPRV proteins when injected into sheep, and the immune response to these proteins should protect against PPRV; however, because not all the PPRV proteins are being made, the set of immune responses will not be the same as seen in real PPRV infection, so it will be possible to determine which animals have been vaccinated and which infected. In order to boost the immune response to the PPRV proteins made by the recombinant FPV, we will include other recombinant FPV expressing sheep immune stimulator proteins. We hope that this will mean that a single dose of the new vaccine will be enough to protect animals, which will decrease the cost of vaccination. We will test the new vaccine in sheep or goats at the research institute in the UK and then further in larger numbers of animals in farms in Uganda where there is a current, ongoing PPR epidemic. This will ensure that protection from infection is still seen when the animals are the types found in developing countries, and kept under the same conditions. Other tasks in Uganda are the testing and validation of a new diagnostic test that will only detect PPRV infection, but not the vaccination, and a 'pregnancy test' style device which will enable the diagnosis of PPR disease directly from a sample of animal tears, without need for a laboratory (so-called 'penside' test). This test will greatly simplify checking for infection in areas where the PPR virus has not yet become established.