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

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.

The morbilliviruses are a discrete genus of negative sense RNA viruses with monopartite genomes. The genus contains a number of viruses of great significance for human or livestock disease. These include the cattle pathogen rinderpest virus (RPV), which is close to official recognition of its eradication, and measles virus (MV), the eradication of which is being discussed. Peste des petits ruminants virus (PPRV) is a morbillivirus that causes disease in sheep and goats. Current live attenuated PPRV vaccines are effective but require a cold-chain for distribution and do not allow the distinguishing of vaccinated animals from those which have recovered from disease. The purpose of the current project is construct and test an alternative vaccine which promises to overcome these defects. The vaccine will be based on recombinant fowlpox viruses (rFPVs) expressing the surface glycoproteins of PPRV (F and H). These will be combined with other rFPVs expressing ovine GM-CSF and/or IL-2 in order to boost the immune response to the vaccine and increase the chance that protection will be achieved with only a single dose of vaccine. The vaccine will be tested both in controlled conditions (animal units at the IAH) and in the field in Uganda. Two new assays will be developed to assist in PPR disease control programmes. A new diagnostic ELISA will be developed which will recognise the PPRV nucleocapsid (N) protein; this assay will be specific for animals that have been infected with PPRV and, coupled with existing assays for antibodies to the PPRV H protein, will allow us to distinguish infected animals from vaccinated animals. We will also work with a commercial partner to develop a pen-side test (lateral-flow device) for PPRV, a test that can be used to rapidly check for PPRV infection in the field.

The principal impact of this project will be to improve PPR disease control through the development of a heat-stable vaccine and associated diagnostic technology in order to differentiate vaccinated from infected animals. The project will also develop rapid on-site diagnostic assays. Ultimate beneficiaries of the combination of vaccine and diagnostic tests will be farmers, village-level livestock keepers and others involved in livestock production and processing in countries which are affected by PPR. This means the benefit should be felt in a large section of sub-Saharan Africa as well as the Middle East and Indian sub-continent. Other beneficiaries of the project will be national veterinary services who, through using a DIVA vaccine strategy, will be able to accurately establish the full extent of spread of the disease through surveillance programmes. This means that vaccination can be carried out with optimal efficiency thus improving the control of the disease. Directly, the Diagnostic Centre in Uganda will have improved capability for diagnosis of PPRV (and other diseases) through both training and the introduction of rapid, sensitive, high-throughput diagnostic assays. These outputs will have a direct impact on local control of livestock disease. The commercial private sector will also be beneficiaries, since they will have the opportunity for commercial development of new diagnostic tests and vaccines. We are presently in discussion with OIE with the aim of setting up an OIE twinning project between the IAH and the DEC. The objective of this twinning exercise is to build on the existing collaborations between the two laboratories and to raise the diagnostic status of the DEC to OIE Regional reference lab for East Africa. This process will improve the dissemination of best practice in the use of the vaccine and the associated diagnostic procedures locally. The FAO are working with partners in a number of countries experiencing outbreaks of PPR and are interested in applying the combination of vaccine and diagnostic tests. Engagement of diagnostic laboratories in neighbouring East African countries and subsequently local veterinarians and communities for use of these vaccines and diagnostic tests will build on existing networks and links. IAH has a product development pipeline which ensures the early identification and protection of Intellectual Property. Genecom is the IAH commercialisation partner and provides documentation and advice on agreements relating to research results, collaborations and exploitation. The penside test will be in the hands of our commercial partner Svanova AB. This product will have an immediate effect in improving the ability of local veterinarians to identify PPR as it moves into new areas; early diagnosis will have a significant effect on limiting spread. For the novel vaccine, we have already made contacts with GALVmed (Global Alliance in Veterinary medicine), who have PPR as one of their targets for improved vaccines and control measures. They will act as the facilitators for putting us in contact with potential commercial partners, in addition to the contacts IAH already has with commercial partners in the developing world (JOVAC, Indian Immunologicals). We will be seeking a commercial partner to whom to licence the ELISA test, in the same way as the IAH has licensed other tests developed in-house. The successful deployment of novel diagnostic tests will require that they are validated to OIE standards and this will be an important goal of the project. The tests can then be included in the OIE Manual, which is available online, and provides detailed protocols for validated diagnostic tests for OIE listed diseases. The IAH is an OIE reference laboratory for a large number of livestock viral diseases and is fully experienced in disseminating standard procedures by this route.