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    Advanced Topics In Resident Health: African Swine Fever – An Overview For Animal Sanctuaries

    light reflects off a window in front of a globe
    Despite the name, African Swine Fever is a global threat to pigs. Photo by Paul Volkmer on Unsplash
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    Veterinary Review Initiative
    This resource has been reviewed for accuracy and clarity by a qualified Doctor of Veterinary Medicine with farmed animal sanctuary experience as of October 2023. Check out more information on our Veterinary Review Initiative here!

    Resource Goals

    1. Learning the basics of what African Swine Fever (“ASF”) is, how it spreads, and how it manifests in pig populations;
    2. Understanding the existing known risks for pig residents in sanctuaries;
    3. And learning about what biosecurity and other measures you can take to protect your pig residents.

    Some Of The Following Information Pertains Specifically To The U.S.
    The Open Sanctuary Project strives to provide resources that can be useful to caregivers worldwide, but when it comes to governmental responses to disease outbreaks, there can be a great deal of variability from one country to the next. While much of the information in this resource should be useful to folks who want to learn more about African Swine Fever, please be aware that we are a U.S.-based organization and some of the following information is focused specifically on the United States’ African Swine Fever Response Plan. Folks living in other parts of the world should check in with their veterinarian or animal health regulatory body for more specific information about the current situation in their region and their government’s response plan.

    While it’s important for animal caregivers to be familiar with some of the more common diseases that could affect their residents, it’s also crucial that they be aware of reportable diseases that affect the species for whom they care, particularly Foreign Animal Diseases (FADs). FADs are diseases that are not typically found in a particular country and that trigger a swift response from governmental agencies focused on containing and eradicating the disease. One such disease for pig caregivers in the U.S. and many other countries is African Swine Fever (ASF). There has never been a reported case of ASF in the U.S., but as reports of ASF outbreaks increase globally (including the first reports in the Americas in almost 40 years), U.S. officials are on high alert. In this resource, we’ll take a look at the basics of this disease, the current situation in the U.S. and abroad, and what pig caregivers can do to help protect their residents.

    The Problem With Naming Diseases After Places
    Historically, human and animal disease names have often incorporated geographical references, perhaps alluding to the suspected place of origin, an area of high risk, or the location of a major outbreak. Such is the case with African Swine Fever. While disease naming practices are not within our control, we would be remiss if we did not highlight the problematic nature of this practice. Not only can naming a disease after a geographical location or labeling it as “foreign” stigmatize that area and contribute to harmful and xenophobic perceptions, but it can also cause confusion about transmission and risk (after all, ASF is a worldwide concern, not one limited to the continent of Africa). Additionally, because of the interconnectedness of our world, associating a disease with a location serves no real benefit, according to Cepheid Senior Director of Medical Affairs Dr. Michael Loeffelholz. In fact, given the ease and volume of global travel, he argues that for many diseases, the place of origin is actually irrelevant. Furthermore, because of climate change, we are seeing altered and expanded ranges for disease vectors such as ticks and mosquitos. As a result, diseases that were previously considered “tropical diseases” are being found in regions they had not been previously. Because of this, he argues, “We really need to focus away [from] using geographic origins in the nomenclature and choose names for viruses that are more relevant to their physical structure or the disease they cause.” To read more about the problem of naming diseases after places, please refer to this article from The American Society For Microbiology.

    What Is ASF?

    ASF is a highly infectious viral disease that can cause severe hemorrhagic disease in domesticated and feral pigs, as well as wild pig species such as warthogs, bush pigs, and wild boars. This disease does not affect humans and also does not appear to affect any species other than those in the Suidae family (pig family). 

    While there are various factors that affect the mortality rate of ASF, mortality can reach 100%. There is currently no effective treatment for ASF, and there are currently no vaccines approved for use in the U.S.

    Because of the highly contagious nature of this virus and the way pigs are intensively farmed, ASF outbreaks have the potential to affect massive numbers of pigs. In addition to mortality from the disease itself, governmental responses to an ASF outbreak often focus on killing infected pigs as well as pigs they may have come into contact with in an attempt to contain and eradicate the disease (this strategy is referred to as “stamping out”). While the focus of ASF is often on the devastating economic impact an outbreak would have on the pig farming industry, compassionate pig caregivers and farmed animal sanctuaries need to understand the threat the virus and governmental response efforts pose to their residents should they find themselves in the midst of an ASF outbreak.

    How Does ASF Spread?

    ASF can spread to pigs via multiple transmission routes. This includes:

    Direct Contact – A pig can become infected by coming into direct contact with an infected pig (wild, feral, domesticated). The virus is found in all excretions and secretions of infected pigs including their saliva, urine, feces, and blood, as well as in their tissues. 

    Indirect Contact – A pig can also become infected via indirect contact. This includes ingestion of food or other substances contaminated with the virus. While not a practice that should occur in sanctuary spaces, ASF can be spread when pigs are fed pig flesh (which might occur when feeding household food scraps or garbage). Additionally, pigs can become infected if their pig food (“feed”) is contaminated, and this is a concern even for vegetarian and vegan food formulas, as certain plant-based ingredients could become contaminated. In addition to ingestion of contaminated foods, pigs can also be exposed to the virus via contaminated fomites such as shoes, clothing, or vehicles, or a contaminated environment.

    A Note On Language
    At The Open Sanctuary, we try to be very careful about our language choices, re-evaluating our current practices as we learn more. Because the word “feed” can be otherizing, we prefer to simply use the word “food” to refer to the things sanctuary residents are fed. However, “feed” does have a specific meaning, and in some cases, using this term is helpful for clarity. The U.S. Food And Drug Administration (FDA) defines “feed” as “food made for animals,” which includes “pet food and pet treats for dogs and cats as well as food for farm[ed] animals.” In this resource, when we use the word “feed,” we are referring to food made for pigs or other non-human animals, such as commercial pig pellets or custom pig food formulas prepared at a feed mill. While food intended for human consumption, such as produce obtained from your local grocery store, may be a potential source of ASF exposure, the literature we reviewed regarding pathways of ASF entry into the U.S. and potential ASF exposure focus specifically on “feed” and “feed ingredients” and not on other types of plant and plant-based foods.

    Vector-borne Transmission – Pigs can also be infected through vector-borne transmission, with bites from soft ticks carrying the virus being the most common example. Ornithodoros ticks are the primary concern where present, and when the virus is present in tick populations, it can make eradication extremely difficult. Evidence suggests that the ASF virus (ASFV) can be maintained in Ornithodoros spp. tick colonies for several years. While there are Ornithodoros tick species in the U.S., according to the ASF Response Plan Redbook, they are unlikely to play a significant role in transmission without a primary wild pig reservoir. There is no evidence that hard ticks (such as the common dog tick or deer tick) can act as biological vectors for ASFV. However, other blood-sucking insects (such as mosquitos or biting flies) might be able to act as mechanical vectors.

    ASFV is highly resistant in the environment, particularly at low temperatures. Estimates from one study suggest that urine can remain infectious for 3 days at 99ºF (37ºC) and 15 days at 39ºF (4ºC). At these same temperatures, feces was estimated to remain infectious for 4 days and 8 days, respectively. The virus can remain viable in blood for up to 18 months when stored at 39ºF (4ºC), and blood from infected pigs typically contains high levels of the virus. In terms of persistence in the tissue, one study suggested that the virus can remain viable in a frozen pig’s body for several years and months in various pig flesh products (i.e., boned meat, salted dried ham).  

    Most common disinfectants are ineffective against ASFV. More information about disinfection can be found in this document from the World Organisation For Animal Health (WOAH), and folks in the U.S. can refer to this table for a list of disinfectants approved for use against ASFV.  

    What Are The Signs Of ASF?

    Clinical signs and mortality rates vary depending on the virulence of the virus strain and the pigs infected. Detection based on clinical signs can be difficult since clinical signs can be variable and can mimic other diseases, including classical swine fever (which is another FAD that the U.S. wants to keep out) as well as diseases that are present in the U.S. such as porcine respiratory and reproductive syndrome (PRRS) and salmonellosis. When ASFV is first introduced to a region, morbidity and mortality rates tend to be higher, whereas once it becomes endemic, there is typically an increase in the incidence of subacute and subclinical infections. Wild species such as warthogs, bush pigs, and giant forest hogs usually develop asymptomatic infections and act as reservoir hosts for ASFV.

    Clinical signs of the acute forms of ASF include:

    • High fever
    • Depression
    • Inappetence
    • Hemorrhages in the skin (ears, legs, and abdomen may appear red)
    • Cyanosis
    • Incoordination
    • Vomiting
    • Diarrhea
    • Bleeding from the nose and/or anus
    • And even death (mortality rates may reach 100%). Peracute infection may result in sudden death without any clinical signs.

    Subacute infections cause similar clinical signs as acute forms, but those signs are typically less severe. Chronic infections cause less specific signs which may include intermittent fever, weight loss, respiratory signs, arthritis, and chronic skin ulcers. Subacute and chronic forms carry lower mortality rates than acute and peracute forms, but the mortality rate can still range from 30-70%. Individuals who survive an ASF infection may become persistently infected.

    What Parts Of The World Have Been Affected By ASF?

    ASF was first described in Kenya, and prior to 1957, ASF was believed to be confined to sub-Saharan Africa but has since spread to other parts of the world. Causes of previous ASF outbreaks include the following:

    • Feeding imported raw or undercooked pig flesh to pigs (this includes legally imported and illegally transported products)
    • Feeding garbage from airports or shipping ports to pigs
    • Movement of infected wild boars

    While some countries that have experienced outbreaks were able to successfully eradicate the disease (sometimes over the course of decades), others have not. Between 2005 and July 2022, 74 countries have reported cases of ASF. Please refer to the World Organisation For Animal Health for updated situation reports regarding ASF cases and areas affected. Your region’s animal health regulatory body may also be a good source of more local information.

    Could ASF Be Introduced To The U.S.?

    As the number of countries affected grows, so too does the risk of ASF making its way into ASF-free countries, including the U.S. Because of the virus’s ability to persist in the environment, on fomites (such as shoes, clothing, or tires), and in pig flesh, human behaviors can play a significant role in transporting it across borders. According to a Qualitative Assessment Of The Likelihood Of African Swine Fever Virus Entry To The United States, the pathway with the highest likelihood to result in human-assisted entry of ASF into the U.S. is the illegal transport of pig products and byproducts. However, entry via the import of plant-based “feeds” and feed ingredients also remains a pathway of concern, as do risks associated with international travel.

    What Is the U.S. Doing To Prepare?

    After the detection of ASF in Haiti and the Dominican Republic in 2021, the U.S. ramped up their efforts to keep ASF out. According to the U.S. Department of Agriculture (USDA), this includes measures such as:

    • Strengthening the partnership between the USDA’s Animal and Plant Health Inspection Service (APHIS) and Customs and Border Protection staff at ports of entry and increased inspection of passengers and products arriving from ASF-affected countries
    • ​​Advanced risk-based restrictions on imports of pig flesh and products containing pig flesh from ASF-affected countries
    • Establishing a protection zone in Puerto Rico and the U.S. Virgin Islands
    • Increasing ASF surveillance testing to help with early detection and increased laboratory testing capacity
    • Updating ASF response plans, including revising the ASF Redbook
    • Enhancing awareness through the “Protect Our Pigs” campaign

    What Will Happen If There Is A Confirmed Case Of ASF In The U.S.?

    As we’ve stated throughout this resource, there has never been a confirmed case of ASF in the U.S. Therefore, unlike for some other diseases, we cannot look back at previous outbreaks to have an idea of what to expect. That said, the U.S. does have an ASF Response Plan that outlines what will likely occur if ASF is confirmed in the country. Below, we’ll summarize the response plan as outlined in the ASF Redbook, focusing on the actions that are most relevant to animal sanctuaries and compassionate pig caregivers, but please be aware that the proposed plan may be revised as the situation develops or as more information becomes available. Folks should defer to their veterinarian and/or animal health officials for the most current information, particularly if they find themselves in a control area during an outbreak. 

    If there is a presumptive case of ASF, the following actions will occur:

    • Quarantine and hold orders will be placed on the infected premise 
    • Confirmatory diagnostics will be performed
    • An epidemiologic investigation and contact tracing will be initiated 

    While waiting on confirmation via laboratory testing, state and/or federal animal health officials will likely begin notifying pig farming operations in what will become the control area upon ASF confirmation. Whether or not farmed animal sanctuaries and other pig caregivers would also be notified may depend on the area and whether or not officials are aware of their presence. 

    Following confirmation of a positive detection of ASF, the following actions will occur:

    • A control area with a perimeter at least 5 kilometers (~3.12 miles) beyond the perimeter of the nearest infected premise/pig will be established
    • Premises that have had direct contact with the infected premise will be quarantined
    • If the detection involves domesticated pigs in the contiguous U.S., an extraordinary emergency will be declared and a 72-hour National Movement Standstill will be initiated

    What Is A National Movement Standstill?
    As mentioned above, if the detection of ASF involves domesticated pigs in the contiguous U.S., a 72-hour National Movement Standstill will be initiated. During this time, all movement of both live and deceased pigs will come to a halt within the contiguous U.S. This movement standstill will give officials time to trace any movement to and from the infected premise so that they can coordinate necessary testing and establish quarantine and control areas. Officials will then announce National Movement Standstill Hour 73 status, communicating whether the standstill will end after 72 hours, will be extended, or will be applied to a more specific geographical region.

    Farms and sanctuaries within the control area may be asked to provide information regarding animal movement as well as the movement of pig “feed”, equipment, personnel, and visitors. Pigs in the control area may also be subjected to mandatory ASF testing, and a positive case will almost certainly result in the compulsory killing (“depopulation”) of all pigs on the premise. Even after the National Movement Standstill concludes, movement of pigs and potential ASF fomites into, within, and out of the control area(s) will require a permit.

    What Can Sanctuaries Do To Protect Their Residents?

    While routine biosecurity will not be enough to protect against ASF, if you do not currently have a biosecurity plan in place, now is the time to change that. ASF is far from the only disease your residents need to be protected from, and a biosecurity plan is one of your best lines of defense against many infectious diseases. You can read more about biosecurity here

    In some cases, establishing a relationship with your state animal health official prior to an emergency can be beneficial, so if you have not already introduced yourself, consider if this is something you should do. These officials or your veterinarian may be able to provide information about any notification systems used to relay information about things like FADs. Identifying ways to stay informed of the current situation is imperative so that you can respond accordingly. 

    While there are certain measures you may need to implement if ASF is detected in the U.S., there are also actions you can take now to help protect your residents from ASF and to ensure you are as prepared as possible should ASF come to the U.S. First, if you live in an area where feral pig populations are present, it is crucial that you take steps to prevent contact between your pig residents and feral pigs (as well as their excretions and secretions). If your current setup does not already do this, we urge you to change this before ASF is detected in the U.S. 

    In addition to contact with feral pigs, be sure to consider other ways your residents might be exposed to ASFV. Most farmed animal sanctuaries have policies in place that prohibit folks from bringing non-vegan food items onto sanctuary grounds, and in addition to this policy being aligned with a farmed animal sanctuary’s philosophy about animals, it also eliminates one of the more common ASF exposure routes. If you do not already have a policy like this, we’d encourage you to implement one now. Additionally, make sure you are not feeding residents food waste that could put them at risk (this is not to say you cannot give your residents that last piece of watermelon sitting in your fridge or a piece of your banana peel – we’re talking about feeding garbage or feeding food scraps from unknown sources here). 

    Also, consider the role vehicles, shared equipment, and human traffic could play in transmission, and find ways to reduce this risk (and be prepared to take more drastic steps if a case is detected in the U.S.). Now might also be a good time to chat with your “feed” supplier to learn what they are doing to prevent contamination of pig “feed” and its ingredients. 

    If you do not currently have robust record-keeping practices in place, this should be another focus area before ASF is detected in the U.S. Record keeping is an important element of animal care regardless of the risk of disease outbreaks, but during a disease outbreak, being able to provide animal health officials with the information they seek is critical. As mentioned above, folks in a control area may need to provide information regarding the movement of pigs (both in terms of intake and transportation off-site) and the movement of humans and potential ASF fomites. You can read more about the importance of record-keeping here

    In addition to the measures described above, you should consult with your veterinarian about what enhanced biosecurity measures you should be prepared to implement if ASF is detected in the U.S., as well as additional measures you might implement if cases were reported in your region. For example, if ASF is detected in the U.S., you may need to consider halting all pig rescue/intake and restricting the humans who are allowed on sanctuary grounds.  

    The thought of an ASF outbreak in the U.S. is both scary and frustrating – scary because of what it would mean for pigs, including those living in sanctuary, and frustrating because there is little farmed animal sanctuaries and pig caregivers can do to prevent ASFV from coming to the U.S. Whatever feelings are elicited by the idea of an ASF outbreak, it’s important that pig caregivers also focus on the things that are within their control. Taking steps now to familiarize yourself with this dangerous disease and its modes of transmission, as well as understanding the proposed governmental response can go a long way in being as prepared as possible. Additionally, considering the ways in which your residents might be exposed to ASFV (such as via contact with feral pigs) and working to reduce or eliminate that risk is crucial. 

    Action Steps

    1. Keep aware of alerts relating to ASF, and consider reaching out to local officials to establish and maintain cooperative communications about any potential of heightened risk.
    2. If you don’t have one, create a biosecurity plan for your sanctuary in conjunction with advice from your veterinarian. If you have an existing plan, revisit it and consult with your veterinarian to analyze whether you can take additional measures to protect your pig residents in our current circumstances.
    3. Assess all ways that your existing practices may potentially expose your residents to ASFV and work to mitigate those risks. This may include:
      1. Preventing contact between your pig residents and feral pigs;
      2. Instituting an absolute prohibition on non-vegan foods on site;
      3. Assessing the food that you currently offer to residents in terms of any potential risk of exposure;
      4. Assessing and revamping your record-keeping protocols to make sure that they are robust enough to accommodate any heightened scrutiny from officials in the case of an outbreak;
      5. And developing an even more heightened biosecurity protocol in conjunction with your veterinarian in advance of any potential outbreak in your region.


    African Swine Fever | USDA APHIS 

    Why Scientists Should Not Name Diseases Based On Location | American Society For Microbiology

    African Swine Fever | World Organisation For Animal Health (Non-Compassionate Source)

    African Swine Fever | Merck Veterinary Manual (Non-Compassionate Source)

    African Swine Fever | The Center For Food Security And Public Health (Non-Compassionate Source)

    African Swine Fever: What You Need To Know | USDA APHIS (Non-Compassionate Source)

    African Swine Fever (ASF): Biosecurity | USDA APHIS (Non-Compassionate Source)

    Risk And Mitigation Of African Swine Fever Virus In Feed | Megan C. Niederwerder (Non-Compassionate Source)

    Qualitative Assessment Of The Likelihood Of African Swine Fever Virus Entry To The United States: Entry Assessment | USDA (Non-Compassionate Source)

    APHIS Celebrates African Swine Fever Preparedness and Prevention Accomplishments | USDA APHIS (Non-Compassionate Source)

    African Swine Fever Response Plan – The Red Book | USDA (Non-Compassionate Source)

    ASF Response Declaration of Extraordinary Emergency & 72-Hour National Movement Standstill | USDA APHIS (Non-Compassionate Source)

    Animal Feed Regulations | U.S. Food And Drug Administration (Non-Compassionate Source)

    Non-Compassionate Source?
    If a source includes the (Non-Compassionate Source) tag, it means that we do not endorse that particular source’s views about animals, even if some of their insights are valuable from a care perspective. See a more detailed explanation here.

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