African swine fever: the disease that is making giant strides
“Entry of ASF into China would have devastating consequences for animal health, food safety, and food security, and raise the possibility of further spread to Southeast Asia including the Korean Peninsula and Japan”. This is what is reported in the document on the risk assessment of the introduction of ASA in China published by the United Nations Food and Agriculture Organization (FAO) in March 2018.
Considering what happened just few months later, the FAO report can be truly considered a Cassandra’s prediction. From mid-tune 2018 ASF was repeatedly notified in China, registering so far up to 20 outbreaks in 8 provinces in less than 2 months, with new cases been reported each week. (ProMED-mail).
Epidemiology
The ASF was firstly described in Kenya in the far 1921 and was recognized as endemic in most sub-Saharan countries. The virus entered in Europe in 1957, causing outbreaks in many countries, including Portugal, Spain, Malta, France, Belgium, the Netherlands and Italy. These outbreaks and those reported in Eastern Europe later, were successfully controlled, resulting in the eradication of ASF from the European continent, although an endemic focus remained in the Italian region of Sardinia.
In 2007 the virus re-appeared in Europe, in Georgia, most probably originating from southwest Africa. From Georgia the disease spread to neighboring countries, including Armenia (2007), the Russian Federation (2007) and Azerbaijan (2008). From the southern Caucasus it continued northward and westward with additional outbreaks to the east of the Russian Federation in domestic pig and wild boar populations. In 2012 and 2013, ASF reached Ukraine and Belarus respectively, while in 2014 outbreaks involving wild boar and domestic pigs were reported in Poland, Latvia, Estonia and Lithuania. In June 2017, further outbreaks occurred in the Czech Republic and Romania.
Here we came to the first giant step: in March 2017 the disease appeared in Irkutsk, Russian Federation, around 2,000 km away from previously reported outbreaks, on the western side of the Russian Federation, and approximately 1000km from the border with China. Most likely this outbreak was due to the movement of infected swine or pig products.
In June 2018 ASF was detected for the first time in China. The disease was observed in a farm near Shenyang City in Liaoning province, where all of the pigs suffered from acute clinical pathological signs, including high fever, dullness, generalized rendering of the skin, obvious enlargement of the spleen and congestion and generalized hemorrhage of the lymph nodes, heart, spleen and kidney. All of the 400 pigs died within one month.
As Chinese authors explained in a published paper: “ the gene sequences from the three farms were the same […] The outbreak strain ASFV-SY18 belongs to genotype II group and shares 100% nucleotide identity with the Follow Using strains : Georgia 2007/1, Krasnodar 2012, Irkutsk 2017 and Estonia 2014 isolated in Georgia , Russia and Estonia based on p72 gene”. In addition, “China has been Russia’s and EU’s important trading partner. In accordance with a liberal trade policy in China, the increasing demand for pork has resulted in a great increase in the volume of live pigs and pork products imported to China. Illegal products imported and waste improperly disposed from international ports and airports to fed pigs are difficult to mitigate. With this outbreak in China, to avoid economic losses, farmers illegally send moribund pigs to local markets, possibly resulting in the rapid spread of ASF to other local farms” (X. Zhou et al., 2018).
As described in the FAO rapid risk assessment, published just few months earlier of the China’s outbreak, “the introduction of ASFV into China could Follow Us different pathways: transport- associated routes, legal and informal swine imports, and legal and informal imports of swine and swine commodities“. Experts agreed that the most likely way of ASF introduction into China was transports routes, Follow Used by illegal imports of food by Chinese migrant workers. Legal imports of pigs were considered unlikely to introduce the disease into the country.
The second long jump of the disease occurred in Belgium at around 1000 km from the first outbreak confirmation. With a dispatch of 13 September, the competent authority of Belgium announced the confirmation of two cases of ASF in wild boar founded dead in the province of Luxembourg in the region of Etalle. Since the first notification, 28 further cases of ASF have been detected in wild boars found dead in the same region. Linda Dixon, researcher in genomics of ASF at the Pirbright Institute in the UK, in an interview with CNN, formulated the hypothesis that infected meat products from ASF-infected areas has been brought and discarded along the main route through this area, but this has not yet been confirmed. There are at least 13 countries so far intending to ban the import of pigs and pork products from Belgium, including Australia, South Korea, Taiwan, China, Belarus, Philippines, Mexico, Japan, South Africa, Singapore, Serbia, Uruguay, and Malaysia (ProMED-mail).
The disease
ASF is probably the most dangerous disease affecting pigs so far, and consequently the whole pork’s market. The disease is high contagious and in domestic pigs highly lethal. The virus, belonging to the family of Asfaviridae Genus Asfivirus , can persist for a long time in the environment and in a variety of swine products , thus leading to a very efficient indirect way of transmission through long distances, as well as the direct way. According to the World Health Organization ASF is not a zoonosis.
The virus may persist for several weeks or months in frozen, fresh or uncooked meat, as well as in salted dried meat products (EFSA Journal, Scientific Opinion on ASF, 2010). By contrast, ASFV is inactivated in cooked or canned hams when these products are heated to 70 °C and in cured or processed products such as Spanish cured pork products (e.g. Serrano and Iberian hams and shoulders) at day 122–140 of curing.
The ASFV infects pigs normally via by either the oral or nasal mucosae, although other routes such as cutaneous, subcutaneous, via tick-bites or scarification have also been reported. Traditionally, virus introduction into free regions may occur as a result of uncooked pork waste–especially from ships and aircraft–being fed to pigs.
Genotypes are used to tracing the origin of ASFV during outbreaks. To date, 22 different p72 (protein 72) genotypes have been identified from East and South African countries. Genotype 1 is predominant in West Africa. Outside Africa, genotype I was the only one found in Europe, America, and the Caribbean, until the introduction of genotype II in 2007 into Georgia in 2007 from East Africa. Current available molecular data derived by using standardized genotyping procedures have indicated the presence of the sole p72 genotype II circulating in eastern European, thus indicating a single introduction in 2007.
The disease mainly spreads by direct contact between sick and healthy animals (domestic pigs and wild Suidae), recovered carrier pigs and soft ticks or, for example, through indirect transmission by lorries, at drinking and eating troughs, via surgical and personal equipment, rodents, or other farm animals. ASF has an incubation period of 4–19 days. Clinical course lasts for 4–5 days in acute infections or longer in cases of the subacute forms of the disease. Usually, peracute and acute, are characterized by a febrile syndrome with erythema and cyanosis of the skin, appear at the beginning of the epidemic, which is characterized by high lethality and the rapid spread of outbreaks. Anorexia, cyanosis and incoordination may occur 1–2 days before death. Mortality rates that decline over time. Infected animals can survive for several weeks and some even recover from the infection and remain sub-clinically infected for a period. In endemic zones, the disease progresses towards subacute and subclinical forms, sometimes due to the emergence of virus strains characterized by moderate or low virulence, which are more difficult to be recognized in the field. In these cases, the infection may persist for several months with no particular obvious symptoms in infected animals other than transient fever, stunting or emaciation, symptoms that may even mimic some other diseases. (Ma Carmen Gallardo et al., 2015).
Survey and control measures
Immediate notification to the European Commission (EC) and to the other EU Member State, stamping out of all the pigs as well as the definition of protection (3 Km) and surveillance (10km) zones with controlled and restricted pigs and pig-products movements must be immediately established (Council Directive 2002/60/EC).
With the Decision 2014/709 of the 9 of October 2014, the EC decided to differentiate states and areas on the basis of the risk level:
- Part I where the risk is due to certain proximity to the infection in the feral population,
- Part II where the disease concern only feral population,
- Part III where the disease concern both feral and holdings populations but the situation is still dynamic with uncertain evolution,
- Part IV where the disease become endemic, concern feral, and holdings pigs, for which at the time of Decision promulgation Sardinia was the unique example.
Control measures took on the basis of this classification includes:
- the prohibition of dispatch of live pigs as well as feral boars, pig meat, preparation, products, as well as consignments of animal by-products, semen, ova and embryo,
- the immediate after use cleansed and disinfection of vehicles,
- the application of special health marks and certification requirements for pigs came from infected areas.
Actually, a vaccine does not exist but for sure, the current situation may be the perfect trigger for increasing the efforts for the development of effective vaccines against ASF.
Figure 1. ASF regionalization according to Decision 709/2014/EU (Source of data: European Commission)
Conclusions
China is the home of around half of the global pig population and has the world’s highest per capita consumption of pork and pork products (FAOSTAT, 2014). Pork productions are estimated to increase in 2018 to 54,75 million tons. Globally, in 2018 more than 361,000 infected wild boars and domestic pigs have been reported to the OIE, with more than 119,000 deaths.
As experts widely explained, the virus Follow Uss transport –associated routes, including trucks, airplanes and ships and it could have probably been introduced into China by the illegal import of infected animals and food products for private consumption or small-scale trade. Other ways potentially resulting in the introduction and spread of ASF are the legal import of infected live pigs or contaminated pig’s products, wild boars cross passing borders and workers abroad, especially those working in the Russian Federation.
On 8 February 2018, the EC requested the European Food Safety Authority (EFSA) to deliver a Scientific Opinion on ASF. The Terms of Reference (ToR) concerned the Follow Using study’s arguments: the density of wild boar population, the epidemiological data to identify threshold in wild boar density do not allow sustaining the disease, the review of the fencing methods available for wild boar in different scenarios and for different objectives. The opinion aimed at proposing and assessing a surveillance strategy, provide sample size, frequency of sampling and identify possible risk groups for early detection of ASF in a naive wild boar population.
A multidisciplinary approach and the control of the wild boar population, since its role in the spread of the disease, will be of fundamental importance to fight the rapid spread of ASF, in particular the study of epidemiological factors, the biology and ethology of the species.
References
- Food and Agriculture Organization of the United Nations. “African Swine Fever Threatens People’s Republic of China “. 6 March 2018. FAO Animal Health Risk Analysis.
- Gallardo C, Nieto R, Soler A, Pelayo V, Fernández-Pinero J, Markowska-Daniel I, Pridotkas G, Nurmoja I, Granta R, Simón A, Pérez C, Martín E, Fernández-Pacheco P, Arias M. 2015. Assessment of African swine fever diagnostic techniques as a response to the epidemic outbreaks in eastern European Union countries: how to improve surveillance and control programs. J Clin Microbiol 53:2555–2565. doi:10.1128/JCM.00857-15.
- Nina Avramova. CNN Interview: Health officials 'very worried' as African swine fever spreads in Europe and Asia. October 2, 2018
- ProMED-mail
- Xintao Zhou, Nan Li, Yuzi Luo, Ye Liu, Faming Miao, Teng Chen, Shoufeng Zhang, Peili Cao, Xiangdong Li, Kegong Tian, Hua‐Ji Qiu, Rongliang Hu. Emergence of African Swine Fever in China, 2018. Transbound Emerg Dis. 2018 Aug 13. doi: 10.1111/tbed.12989.
Valentina Zenobio (COVEPI)
