African Swine Fever and Classical Swine Fever: Differences and Similarities

Since 2014, an outbreak of the viral disease African Swine Fever (ASF, not to be confused with Classical Swine Fever, or CSF) — which is not transferable to humans but has almost a 100% mortality rate (for the most virulent forms) in swine — has been occurring throughout Europe and Asia, affecting and killing hundreds of thousands of bush pigs, warthogs, wild boars, and domestic pigs.

ASF is a highly virulent disease from the Asfarviridae family (its only genus is Asfivirus)

and is made up of a double stranded DNA-containing icosahedral capsid.

The virus has been found in bodily fluids such as blood, nasal fluid, feces, semen, and urine, and infection can occur either directly (through contact with infected animals) or indirectly (through consumption of infected meat, Ornithidoros ticks, or contact with or ingestion of disease-carrying objects like clothes or vehicles). Humans are often the cause of outbreak due to modern marketing conditions, which make it more difficult to control the movement of goods or, on a smaller scale, by leaving uncooked carcasses out where they can be ingested by swine.

Because there is no known vaccination against African Swine Fever, most prevention methods are related to hygiene, biosecurity, and control of trade and the buying and selling of pigs. Depending on the virulence (peracute, acute, subacute, or chronic) of the virus, infected animals may present themselves with hemorrhaging, high fever, sudden death, vomiting, diarrhea, abortion, reduced appetite, and lesions. Mortality rates and times also vary with virulence, ranging from 90-100% mortality in peracute (very sudden death) and acute cases (death in 6-20 days), 30-70% in subacute (death in 15-45 days), and even lower in chronic cases.

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Animals who are affected with and survive chronic ASF can sometimes become carriers for the virus. R0, or how many animals one affected animal will infect, also varies with virulence and is affected by whether or not spread happens through direct or indirect transmission. It impossible to distinguish African Swine Fever from Classical Swine Fever without laboratory examination.

Classical Swine Fever (CSF), often referred to as hog cholera, is extremely similar to ASF in that it only affects swine, generally has a very high mortality rate, develops similar symptoms, and is transmitted both indirectly and directly, but there are also some key differences. The hog cholera virus, which has an incubation period of 2 – 15 days, is of the genus Pestivirus in the Flaviviridae family and holds single-stranded RNA rather than the double-stranded DNA of ASF. Hog cholera can also be divided into four different severity categories: acute (death after 5-25 days), chronic (death follows apparent recovery), congenital (may or may not die, depending on strain), and mild (also depends on strain), each of with come with different symptoms including fever, hemorrhaging, swollen lymph nodes, vomiting, constipation and then diarrhea, fetal death or abortion, weakness, and poor growth.

Transmission of Classical Swine Fever happens mainly orally or oronasally through direct contact with infected animals, and indirect contact with things like vehicles, people, clothes, and instruments and needles. In addition, it can be transmitted through inhalation of airborne disease, usually coming from high density pig farms. Similar to African Swine Fever, populations of wild boar are often infected through the consumption of infected carcass left behind by humans, also increasing the risk for surrounding domestic pigs. Unlike ASF, ticks or any other insects are not vectors for disease. A major issue of CSF is the infection of fetuses within the womb, which can lead to persistent infection, abortion, and stillbirth. Additionally, R0 remains heavily dependent on the virulence of the strain as well as the density of the population. While vaccines protecting from hog cholera exist, there are no known treatments for the virus.

For both types of swine fever, lack of treatment and exceedingly high virulence and mortality rates mean that when animals are infected, they must be immediately slaughtered and disposed of and the surrounding area must be sterilized, followed by close surveillance in order to prevent further spread of the disease. Both ASF and CSF are able to survive for very long periods of time in cold conditions and less so in warmer temperatures, so they are greatly affected by climate change. They are also able to survive well in pork products and on surfaces, like transport trucks or slaughterhouses, that come into contact with infected swine. As a result, biosecurity is extremely important in preventing the spread of virus, in addition to having well-kept records on all swine, specifically wild boars, which are much more difficult to control.

ASF and CSF: Spread

In 1833, the first cases of hog cholera were reported in Ohio, USA. Later, from 1860 to 1970, it was found throughout North America and Europe, where multiple have outbreaks occurred in places such as the Netherlands and Germany, with the worst occurring in the late 1990s. The disease remains endemic in parts of Asia, Europe (specifically Latvia), and Central and South America. The prevalence of CSF in Africa is unclear due to insufficient surveillance. As of 1978, hog cholera has been eradicated from North America, parts of Central and South America, and is also not present in Australia. Today, Classical Swine Fever outbreaks are not a major issue compared to those of African Swine Fever, which is currently an epidemic in China and Europe.

While CSF epidemics do not pose a major threat right now, they most definitely have in the past. In 1997-1997, the Netherlands witnessed the infection of 400+ herds, and the deaths of about 12 million swine. Over 2 billion dollars were spent in eradication efforts. More recently, a single outbreak of hog cholera was reported in Japan, where it had previously been virus-free since 2007, in September 2018 on a farm in the Gifu province containing 610 pigs. Luckily, due to its proximity away from other farms, no additional cases have been reported since (except for a few wild boars inside of the restriction zone) and the area is expected to be considered disease free by December 12, 2018. Past outbreaks have also occurred across Europe. Due to the existence of a vaccine, the spread of CSF is not as predominant as that of ASF.

The first case of African Swine Fever that was distinguished from Classical Swine Fever occurred in 1910 in Kenya, where it mostly circulated throughout the African countries until 1957, when it was introduced to Portugal in 1957, where it was eradicated, but then returned and spread through several European countries in 1960. In addition to several European countries, like Italy, where it is still endemic in Sardinia, ASF spread to countries in South and Central America, where it has since been eliminated. In the 2000s and 2010s, outbreaks were reported throughout Eastern Europe through Lithuania, Latvia, Estonia and Poland. It is still prevalent in these countries, but mostly among wild boars. African Swine Fever remains widespread throughout Africa.

An epidemic of African Swine Fever, which began in 2014, is currently spreading across Europe and China, resulting in the culling of a total of over 150,000 swine due to the extremely contagious nature of the disease — when one animal is infected, the whole surrounding population of swine must be culled to prevent further spread. A Chinese slaughterhouse is the most recent site of outbreak, with 8 Chinese provinces also reporting a total of 29 cases. In Europe, most outbreaks have been concentrated in Romania, Estonia, Latvia, Lithuania, and Poland. While some outbreaks affect only a few backyard pigs, others can result in the deaths of thousands due to the high concentrations of pig farms and slaughterhouses. The disease spread to Western Europe and China in late September (2018) was likely caused by humans who leave contaminated meat products in the forest, where wild boars can consume them. Additionally, because the illegal and legal trade of swine and pork products is so prevalent and uncontrollable, it is exceptionally difficult to find the original cause of the virus and the movement of these products is another probable cause for outbreak. Since the outbreak began, there have been over 355,000 cases reported in Europe, and 361,000 globally.

Both African Swine Fever and Classical Swine Fever are extremely contagious viruses that present themselves in very similar ways. Because both viruses are so easily spread and widely distributed, it is very important that detailed records be kept so that the locations and severity of each outbreak are clear and accessible. This way, proper measures, such as the culling of swine and careful observation at places of infection, can be taken in an attempt to control the risk of epidemic. When instances are not reported, it is more than likely that the amount of cases, not only in places where they are endemic but also throughout the world and in places where they have previously been eradicated, will increase.

ASF and CSF: Impact

Neither African Swine Fever nor Classical Swine Fever cause adverse effects when infected products are ingested by humans. The economic effects, however, are much greater, especially for the pig farmers or owners themselves. When a pig is infected with AFS or CFS, in most cases, the whole population must be slaughtered in order to prevent further spread of the disease. As a result, the farmer loses much of the income from those pigs as the value of the pork products decreases. This was seen in Poland (when instances of disease began to increase) when an estimated 855 million US dollars decrease in export value occurred in 2014 and 2015. In those same years, the values for Lithuania, Latvia, and Estonia also dropped heavily. The effects on China may be even more drastic, as it houses almost half of the worldwide pig population and is the greatest consumer per capita of pork products. Due to the nature of AFS and CFS, the transcontinental transport of pork products is very highly regulated, and the epidemics may negatively affect food security for many people around the world. There are also undoubtedly the extremely negative impacts on swine health, with a massive amount of swine killed either directly as a result of being infected with the disease, or indirectly to prevent additional instances and outbreaks. Overall, both African Swine Fever and Classical Swine Fever have a particularly negative impact on humans and animals alike.

ASF and CSF: Sources of Information

The information for this paper is mainly sourced from government websites, as well as the Encyclopedia Britannica and CNN, a major news outlet. A major source of information was the World Organization for Animal Health (OIE), which is made up of delegates from a number of different member countries, which work together in order to publicly document issues and information regarding worldwide animal health and to notify the public of both health standards for animals and information about said diseases. Another source was the National Center for Biotechnology Information (NCBI), which, as part of the United States National Library of Medicine, gives people access to information about biomedical and genomic matters. Information from the United Kingdom Department for Environmental Food and Rural Affairs, the United States Department of Agriculture (USDA) Foreign Agricultural Service (FAS) and Global Agricultural Information Network (GAIN), as well as the Food and Agriculture Organization of the United Nations (FAO) was also heavily utilized. All of these sources are from websites that use professional, experienced writers and editors and that have a high standard of reporting factual and credible information.

ASF and CSF: Credibility of Information

It is difficult to find and use only credible information when researching a topic because there are so many different possible sources available on the internet. As a result, all of the material for this paper was gathered with conscious effort to only pull from reliable websites — such as those of government organizations (ending in .gov or .uk etc.), widely known outlets like CNN, and the generally dependable and consistent Encyclopedia Britannica. Many of the chosen sites specified that contributions, writing, and edits had been made by professionals, such as veterinarians and other experts. Furthermore, the fact that most sites are government websites means that research was funded and undertaken by highly qualified specialists and that topics were thoroughly investigated and fact-checked before publishing. Additionally, all of these sources are usually unbiased and closely edited. Another sign that all of the sources were trustworthy is that they were published or updated recently, which provides information reflective of the current state of, in this case, African Swine Fever or Classical Swine Fever. While no information is guaranteed to be 100 percent accurate and reliable, the sources for this paper were carefully chosen in an attempt to convey material that is as credible as possible.

ASF and CSF: How much information is enough?

After finding all of my credible sources on the internet, I was able to determine that I had enough information — to the point where I was confident enough to begin writing this paper — when the data began to overlap for each website, and, when reading new articles, I no longer found any new material. From that point, I was able to narrow down exactly the sources I was going to use by finding the most reliable of those websites and using their information to write a fully informed essay. Furthermore, when I knew that I was able to fully understand the topic from my online research, I felt that I could inform others in depth about the severity of African Swine Fever and Classical Swine Fever. I also decided that I had enough information when I felt that I could easily reinforce and explain any claims that I made about the diseases and had a long list of trustworthy resources to further back up said claims, in order to avoid any discussion that is not grounded in concrete facts. Only after spending numerous hours critically analyzing information and researching and selecting my sources, I felt that I had a sufficient amount of information to write a cognizant essay.

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