An imminent threat to the South African wool, sheep and goat industries called PPR virus, and the urgent need for an appropriate Vaccine
Dr Baty Dungu
- Agriculture & Livestock production have always been important contributors to the SA economy.
- Due to the burden of animal diseases, some of which are unique to Africa, South Africa has relied on several animal vaccines for more than 100 years to ensure effective livestock production. To mention but a few: the keeping of horses and wool sheep in South Africa has been possible thanks to vaccines such as those against African horse sickness and bluetongue respectively. South Africa was the first country in the world to describe the viruses causing these two dreadful diseases and developed these 2 vaccines around 1904.
- To date, SA has been able to establish a vibrant wool industry, which, according to industry statistics, counts more than 15 million wool sheep, of which 4 million sheep are owned by the emerging and communal sector. With a total production of around 45 million kg of wool per annum – more than 90% is exported, essentially to China, Italy, and other big international markets. SA produces 2-3% of the wool globally, and about 12% of the world apparel (fine) wool. This multi-billion industry relies on around 6 000 commercial and 4 000 communal wool producers in South Africa. The emerging sector produces about 13% of the national clip.
- More importantly, the wool industry employs 35 000 farm workers as well as 4 000 sheep shearers and wool handlers.
- This vibrant economic sector of our country could be in jeopardy due to serious animal diseases. One such disease is Peste des Petits Ruminants known globally as PPR, a disease caused by a virus of the same family as the causative agent of the now eradicated Rinderpest. PPR is currently one of the most important small ruminants (sheep and goats) diseases globally, with massive negative economic and livelihood impacts.
- Once introduced to a new country, the virus has been shown to be capable of infecting up to 90 percent of a flock, and the disease kills anywhere from 30 to 70 percent of infected animals. Luckily, the PPR virus does not infect humans. Spreading fast in recent years, more than 70 countries in Africa, the Middle East and Asia have to date confirmed PPR within their borders, and many countries are at risk of the disease being introduced. These regions are home to approximately 1.7 billion heads – roughly 80 percent – of the global population of sheep and goats.
- Recent experience in areas where the disease had spread is that, sadly, once established, it becomes very difficult to eradicate. Morocco is one of the very few countries that managed to eradicate the disease after the incursion but sadly got reinfected again a few years later. Large countries with extensive resources like India and China have been battling with the disease. In India, the PPR associated annual losses have been shown to vary between the US $653 million and $669 million (more than R10 billion!). Closer to us, a massive outbreak in the naïve small ruminant population in West DR Congo up to 2012 resulted in recorded deaths of 744,527 goats, which converted to a trade value of USD 35,674,600 (more than R565 million). These are underestimated figures, and the disease has since become endemic, causing further economic damage.
- South Africa is at great risk as the disease has spread southward in recent years on the African continent, reaching, and establishing itself already in Tanzania and Angola. There have been brief intrusions into Zambia which, luckily were short-lived.
- However, with the spread seen in other regions, including Asia and the Middle East, PPR may likely continue its spread south and reach South Africa.
- With a fully naïve population of sheep and goats in South Africa, an introduction will be devastating as high morbidity and mortality can be expected, thus compromising the lucrative wool industry, food security and the tens of thousands of jobs in the sector.
- It has been declared by the global animal health and livestock community is the next disease to be eradicated from our planet. Meanwhile, while not occurring in South Africa, it is a serious threat to our country as it has been spreading southward on the African continent. More worryingly, once in a country, it has been difficult to eradicate, without sustained coordinated efforts, thus resulting in catastrophic losses for the sheep and goat industries, and subsequently the livelihood of millions of people.
- Preventing its entry into South Africa should therefore be a priority, with a preparedness program including surveillance activities and rapid detection capacity.
- At the first indication of entry or imminent risk, two options could be considered for South Africa: stamping out or targeted slaughter of infected or exposed animals, and vaccination. With the disease not always being easy to detect, stamping out will be difficult to effectively implement.
- Vaccines against PPR do exist, and the most used one is based on a live attenuate (weakened) virus isolated from Nigeria and called the Nigeria 75/1 vaccine. This vaccine, which has been very successful in controlling the disease, is produced by many vaccine manufacturers and is widely used in infected countries, including countries like China.
- Vaccination, clearly a critical tool for PPR, should be part of a well-structured control program.
- Given the PPR free status of South Africa, a vaccination strategy will require serious considerations in terms of the approach to be adopted.
- As stated earlier, the currently widely used vaccine, the Nigeria 75 strain, is a live attenuated virus, which causes an infection that doesn’t lead to the disease, but rather builds a protective immunity in vaccinated animals. As is the case with many other vaccines, vaccinated animals can be identified by blood tests that detect antibodies generated by the vaccine. Sadly, infected animals also will test positive in the same way as vaccinated animals. It becomes therefore difficult to differentiate vaccinated from infected animals during the control of the disease. This phenomenon is not seen as a problem in already infected, endemic countries where the disease has been established.
- In PPR-free countries like South Africa, if the disease had to suddenly enter, it will be important to detect infected animals without confusing them with possibly vaccinated ones. The differentiation of infected from vaccinated animals, called in short DIVA, can be made possible when vaccines lacking the section detected by the test are used. These are called marker or DIVA vaccines.
- South Africa will therefore require a critical tool in the control of PPR, a DIVA vaccine. This could already be stockpiled in vaccine banks and be used as soon as the disease reaches our neighbouring countries or when the danger of entry becomes very important.
- Sadly, such PPR DIVA vaccines are not widely available and are not produced in South Africa. Globally to date, two PPR DIVA vaccines have been fully developed and almost ready for large scale use. Other candidate vaccines are at different stages of evaluation. Based on recent experience with the weakening South African veterinary vaccine sector, we may not have the time and capacity here in South Africa to start the development and production of a suitable PPR DIVA vaccine. It would be wiser to either arrange the registration of one of the two DIVA PPR vaccines mentioned earlier or license the technologies where it is available. These arrangements could then lead to possible emergency purchases when the need arises or the establishment of virtual or physical PPR vaccine banks.
- However, this process will be stretched, and we may not have the luxury of time to be ready to face the threat.
- The urgency for actions toward PPR preparedness for South Africa is clearly a no-brainer. The South African wool industry, and more specifically Capewool, has been working toward a vaccine availability plan but requires support and mobilisation of the whole livestock sector.
- The potential disastrous impact of PPR, primarily on the wool, sheep, and goat industries, but equally on both food security, employment and South African economy, as a whole, should wake us up to avoid surprises and avoid seeing the disease establish itself in South Africa, with lasting consequences that will be difficult to address.
Dr. Baty DUNGU is a veterinarian with PhD in vaccinology and more than 20 years’ experience in vaccine development and manufacturing. In addition to his South African vaccine activities, he is one of 6 members of the World Animal health organisation Scientific Commission, panellist of the One Health High Level Expert Panel (established by WHO, FAO, OIE and UNEP), board member of the International Veterinary Vaccinology Network and Member of the Group of Experts on Animal Health for the African Union.