By Diane DeWitte, UMN Extension swine educator
Written for submission to The LAND - as April 24 2026 Swine & U column
In 2015, when Highly Pathogenic Avian Influenza (HPAI) struck Minnesota poultry, hitting the US’s number one turkey producing state especially hard, Extension livestock educators took note. Poultry producers and allied agencies developed efficient methods to depopulate and dispose of sick and dead birds.
The pig industry began to prepare, in 2018, for African Swine Fever (ASF), which blew up in China but had never been in our hemisphere. Potential outbreak preparation in swine involved the creation of practical ways to depopulate and dispose of sick hogs. ASF now lives in the Dominican Republic and Haiti, under careful monitoring by the USDA.
Both are viruses and both have broken out repeatedly across the globe. March 2024 was the advent of HPAI virus infection of dairy cows. Extension educators and researchers, working with UMN veterinarians, began to call it the H5 virus, causing influenza no longer specific to birds, but possible in all animals.
H5 influenza is spread by migrating wild waterfowl, and because Minnesota is in the upper part of their migratory flyway, infections readily spread as they fly south in the winter. Wild waterfowl movement ensures a high likelihood of movement of the H5 virus. More recent research has shown H5 in wild mammals and domestic cats.
Commercial swine producers fight influenza regularly, and part of Pork Quality Assurance Plus (PQA+) training for pig farm team members is a module on zoonotics, those diseases which can pass back and forth between animals and humans. A common recommendation for people who work with swine is to get an annual flu vaccine to limit the chance of spreading illness to the pigs in the barn.
Extension’s H5 influenza group, comprised of poultry and livestock species educators, meets weekly to address outbreaks, signs of disease issues, and the latest virus and disease research. Initially formed to monitor H5 activity, the group has recently turned its attention to what was initially a cattle issue south of the border.
New World Screwworm (NWS) was eradicated in the United States in 1966 but is endemic in some South American countries as well as Cuba, Haiti and the Dominican Republic. It currently is not present in the United States, but in November 2024 it made an appearance in Central America and Mexico and has moved closer to the southern US border. USDA Animal & Plant Health Inspection Service (APHIS) is working closely with state animal health officials, particularly in Texas, and with Texas A&M University to monitor the situation and take steps to keep NWS out of the country. Currently all southern ports of entry are closed to livestock trade.
NWS does devastating damage to live animals when the fly’s larvae burrows into the tissue of a wound. Adult screwworm flies, (NWS, Cochliomyia hominivorax), lay eggs on the edges of an open wound in a live animal. Within hours, the eggs hatch into larvae which burrow into the wound to feed. This makes the wound worse, attracting more flies which lay eggs. After feeding in the live animal for a week, the larvae drop to the ground and burrow into the soil to pupate. After a minimum of seven days in the ground, adult flies emerge. The pest is called “screwworm” because when the larvae burrows into the animal’s flesh the resemblance is to a screw driving into wood.
The parasite can affect any mammal, including swine, cattle, wildlife, pets, and even humans. Because the fly is attracted to open wounds, it presents a risk in any type of livestock production system. If infestations are not treated promptly, the damage can become severe and may even lead to the death of the affected animal.
USDA APHIS has responded with a robust plan for detection and eradication. One proven method of preventing NWS is the use of sterile insect technology (SIT). Because a female NWS fly only mates one time, USDA has developed a program of sterilizing male flies and releasing them in known NWS locations. A female mated to a sterile male cannot produce viable eggs. Currently the USDA works with Panama to produce 100 million sterile flies per week. Additional funding helped build a domestic insect rearing facility at Moore Air Base in South Texas. APHIS funding also has assisted Mexico in renovation of its own sterile insect facility, with the plan to add an additional 60-100 million sterile flies to the numbers produced.
USDA continues to disperse millions of sterile insects per week in Mexico and closely evaluates the location and circumstances of each new NWS case to adjust sterile insect release efforts and locations as needed. Changes to the sterile insect dispersal area, or polygon, in Southern Mexico occur as needed to maintain broad suppression and help prevent the pest from moving further north toward the United States.
The Swine Health Information Center (SHIC) has released a new fact sheet on NWS. The educational resource was recently highlighted in SHIC’s newsletter. Spearheaded by Dr. Lisa Becton, Associate Director at Swine Health Information Center, the fact sheet is available online and was developed through a collaboration between the Swine Health Information Center and experts at Texas A&M University. The fact sheet can be found at swinehealth.org.
The resource was designed specifically for the swine industry and includes:
The full New World screwworm fact sheet is available through the Swine Health Information Center website at swinehealth.org, where producers can download the guide and review recommended reporting procedures.
Here in Minnesota, the Minnesota Board of Animal Health (BAH) has implemented new importation requirements for dogs and cats entering Minnesota from Mexico due to increased cases of NWS in that region. Animals imported from these areas may be subject to a supervised quarantine period in Minnesota and any signs of potential infection must be immediately reported to the BAH. Minnesota’s BAH is working alongside the USDA and CDC to protect against the spread of NWS.
At our weekly Extension, animal science and veterinary H5 meeting, we first review the latest H5 influenza news, then address NWS issues. As summer approaches, pig farmers who closely observe swine activity and any new wounds can help the industry prevent infection by NWS.
Information gathered from Minnesota Board of Animal Health, Swine Health Information Center, and USDA-APHIS. Diane DeWitte is an Extension Swine Educator based in Mankato, MN. She can be reached at stouf002@umn.edu.
Written for submission to The LAND - as April 24 2026 Swine & U column
In 2015, when Highly Pathogenic Avian Influenza (HPAI) struck Minnesota poultry, hitting the US’s number one turkey producing state especially hard, Extension livestock educators took note. Poultry producers and allied agencies developed efficient methods to depopulate and dispose of sick and dead birds.
The pig industry began to prepare, in 2018, for African Swine Fever (ASF), which blew up in China but had never been in our hemisphere. Potential outbreak preparation in swine involved the creation of practical ways to depopulate and dispose of sick hogs. ASF now lives in the Dominican Republic and Haiti, under careful monitoring by the USDA.
Both are viruses and both have broken out repeatedly across the globe. March 2024 was the advent of HPAI virus infection of dairy cows. Extension educators and researchers, working with UMN veterinarians, began to call it the H5 virus, causing influenza no longer specific to birds, but possible in all animals.
H5 influenza is spread by migrating wild waterfowl, and because Minnesota is in the upper part of their migratory flyway, infections readily spread as they fly south in the winter. Wild waterfowl movement ensures a high likelihood of movement of the H5 virus. More recent research has shown H5 in wild mammals and domestic cats.
Commercial swine producers fight influenza regularly, and part of Pork Quality Assurance Plus (PQA+) training for pig farm team members is a module on zoonotics, those diseases which can pass back and forth between animals and humans. A common recommendation for people who work with swine is to get an annual flu vaccine to limit the chance of spreading illness to the pigs in the barn.
Extension’s H5 influenza group, comprised of poultry and livestock species educators, meets weekly to address outbreaks, signs of disease issues, and the latest virus and disease research. Initially formed to monitor H5 activity, the group has recently turned its attention to what was initially a cattle issue south of the border.
New World Screwworm (NWS) was eradicated in the United States in 1966 but is endemic in some South American countries as well as Cuba, Haiti and the Dominican Republic. It currently is not present in the United States, but in November 2024 it made an appearance in Central America and Mexico and has moved closer to the southern US border. USDA Animal & Plant Health Inspection Service (APHIS) is working closely with state animal health officials, particularly in Texas, and with Texas A&M University to monitor the situation and take steps to keep NWS out of the country. Currently all southern ports of entry are closed to livestock trade.
NWS does devastating damage to live animals when the fly’s larvae burrows into the tissue of a wound. Adult screwworm flies, (NWS, Cochliomyia hominivorax), lay eggs on the edges of an open wound in a live animal. Within hours, the eggs hatch into larvae which burrow into the wound to feed. This makes the wound worse, attracting more flies which lay eggs. After feeding in the live animal for a week, the larvae drop to the ground and burrow into the soil to pupate. After a minimum of seven days in the ground, adult flies emerge. The pest is called “screwworm” because when the larvae burrows into the animal’s flesh the resemblance is to a screw driving into wood.
The parasite can affect any mammal, including swine, cattle, wildlife, pets, and even humans. Because the fly is attracted to open wounds, it presents a risk in any type of livestock production system. If infestations are not treated promptly, the damage can become severe and may even lead to the death of the affected animal.
USDA APHIS has responded with a robust plan for detection and eradication. One proven method of preventing NWS is the use of sterile insect technology (SIT). Because a female NWS fly only mates one time, USDA has developed a program of sterilizing male flies and releasing them in known NWS locations. A female mated to a sterile male cannot produce viable eggs. Currently the USDA works with Panama to produce 100 million sterile flies per week. Additional funding helped build a domestic insect rearing facility at Moore Air Base in South Texas. APHIS funding also has assisted Mexico in renovation of its own sterile insect facility, with the plan to add an additional 60-100 million sterile flies to the numbers produced.
USDA continues to disperse millions of sterile insects per week in Mexico and closely evaluates the location and circumstances of each new NWS case to adjust sterile insect release efforts and locations as needed. Changes to the sterile insect dispersal area, or polygon, in Southern Mexico occur as needed to maintain broad suppression and help prevent the pest from moving further north toward the United States.
The Swine Health Information Center (SHIC) has released a new fact sheet on NWS. The educational resource was recently highlighted in SHIC’s newsletter. Spearheaded by Dr. Lisa Becton, Associate Director at Swine Health Information Center, the fact sheet is available online and was developed through a collaboration between the Swine Health Information Center and experts at Texas A&M University. The fact sheet can be found at swinehealth.org.
The resource was designed specifically for the swine industry and includes:
- Details and imagery of the life cycle of NWS
- Photos to illustrate specific examples of infestation in swine
- Discussion of clinical signs and wound care
- Recommendations to manage housing and the environment regarding NWS
- Information on sample collection, and encouragement to involve the veterinarian immediately
The full New World screwworm fact sheet is available through the Swine Health Information Center website at swinehealth.org, where producers can download the guide and review recommended reporting procedures.
Here in Minnesota, the Minnesota Board of Animal Health (BAH) has implemented new importation requirements for dogs and cats entering Minnesota from Mexico due to increased cases of NWS in that region. Animals imported from these areas may be subject to a supervised quarantine period in Minnesota and any signs of potential infection must be immediately reported to the BAH. Minnesota’s BAH is working alongside the USDA and CDC to protect against the spread of NWS.
At our weekly Extension, animal science and veterinary H5 meeting, we first review the latest H5 influenza news, then address NWS issues. As summer approaches, pig farmers who closely observe swine activity and any new wounds can help the industry prevent infection by NWS.
Information gathered from Minnesota Board of Animal Health, Swine Health Information Center, and USDA-APHIS. Diane DeWitte is an Extension Swine Educator based in Mankato, MN. She can be reached at stouf002@umn.edu.
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