Interview about the impending screwworm threat

Chris Lee Screwworm interview

Screwworms may not be top of mind for most veterinarians today, but that could soon change. Once eradicated from the United States, these parasites have been steadily moving northward through Central America and have now reached Mexico. In this interview with 

, Christopher Lee, DVM, MPH, DACVPM, explains why the potential return of screwworms is a serious concern, how they differ from other maggot infestations, and what veterinarians need to know to be prepared if the spread continues in the US. 

Screwworm case in Mexico prompts emergency response in the United States


All right. Well, thank you for having me. My name is Christopher Lee. I'm a preventive medicine specialist. I've worked across the board in veterinary medicine, from scrubbing kennels as a young kid to being an associate, a medical director, and an owner. I've done emergency medicine, day practice, and I still do a lot of ER work.

Recently, I was honored to be part of the editorial advisory board for 

, and I am also one of the NAVLE item writers. So, for those who have recently passed the boards—I do apologize—because a lot of those questions were mine!

I'm looking forward to talking about screwworms. It's something we haven't thought about for quite a while. While the government does worry about it, it has always seemed theoretical—probably not an immediate concern. However, it is something that could impact all of us, and the implications are terrifying.

To put it into perspective: if we look back at white-tailed deer in the southeastern United States and across the country, in 1950, we had fewer than half a million deer, and they were under threat. There were other factors involved, but screwworms alone were threatening extinction in certain areas.

By 1966, screwworms were eradicated from the U.S., and within 10 years, the deer population increased tenfold. That is the kind of impact we are talking about.

I recently saw a video and a picture while talking to a friend. We were looking at a deer that had been invaded by screwworms. The parasites had burrowed through the skin, through the muscle, and through the bone—into the brain. And the poor animal was still alive.

Screwworms belong to the genus and species 

, which is the New World, or Western Hemisphere, screwworm. It has always been present in South America, but over the last few years, we've seen a steady northward movement.

It has spread through all of Central America and has now reached Mexico. The question of whether it will arrive in the United States is not "if," but "when." If that happens, we will see myiasis cases on a regular basis.

What makes the New World screwworm so concerning is that it causes primary myiasis. To clarify, myiasis occurs when a human or animal has live maggots feeding on them. Right now, in the US, we only see secondary myiasis, which means maggots are feeding on dead or decaying tissue.

For example, if you're a large or small animal veterinarian and you see an animal with maggots, you always ask, 

 As an ER vet, I see this regularly. It’s dramatic when people see maggots in a wound, but as a clinician, I recognize that secondary myiasis can actually be beneficial—maggots clean out dead tissue and help prevent gangrene.

However, primary myiasis is a different story. 

 is an obligate parasite, meaning it requires 

 tissue to survive. That’s what makes it so frightening—you don’t need an existing wound or infection for an animal or human to be infested.

If screwworms establish themselves in the U.S. again, we will be facing a severe and urgent problem in veterinary and public health.

Videos

With screwworms advancing northward into Mexico, veterinarians must prepare for the possibility of widespread infestations

Screwworms are moving north—are we prepared?

C Malambo/peopleimages.com/stock.adobe.com

Royal Canin, a global leader in pet health nutrition and one of the billion-dollar brands of Mars, Incorporated, announced during this year’s Veterinary Meeting & Expo (VMX) that it is launching a new user-centric version of the Royal Canin Academy. According to the release, the transformation is aiming to make the learning journey for its users more engaging, efficient, engaging, and intuitive.

"For more than 50 years, Royal Canin has advanced the knowledge and understanding of pet health and nutrition, and the desire to share this knowledge led to the creation of the Royal Canin Academy," said Todd East, DVM, director of veterinary affairs, Royal Canin North America, in an organizational release.

Enhancements to the Royal Canin Academy platform include flexible learning, mobile learning and accessibility, updates to the interface, improved performance, and more. The veterinary professionals using the platform will have the ability to also access tailored course management, personal progression tracking, training resources, and step-by-step guides with users being able to select the methods that they learn best with.

"Now is the time to reimagine this platform in an industry where innovation is constantly surrounding us. This industry-leading platform will continue to expand upon Royal Canin's mission of educating pet professionals in a seamless and more impactful way," East continued.

To give back to their community, when a veterinary professional signs up for the Royal Canin Academy in 2025, Royal Canin will donate 4 meals to pets in need through the company’s partnership with Greater Goods, up to a limit of 60,000 meals donated to pets in need, according to the release.

Royal Canin was founded in 1968 by Jean Cathary, DVM, when during his career, he began to realize that food can have an impact on the health of animals.

 This lead him to create “yellow soup” for dogs, and the Royal Canin brand was registered. Four years later, the company was acquired by Guyomar’h Groupe, which brought to the company its expertise in diet formulation and nutritional precision.

Royal Canin would go on to be launched in the United States in 1985 with 4 importers before Guyomar’h Groupe was purchased by Paribas Affaires Industrielles, creating a shift in strategic direction, global development, and a geater ambition. Over the next couple of decades, Royal Canin would become part of Mars, Inc. and continue to expand its portfolio to become the pet food company it is known for today.

Royal Canin Academy Announces Advancements to Digital Learning Platform at VMX 2025. News release. Royal Canin. January 21, 2025. Accessed February 4, 2025. 

https://prnmedia.prnewswire.com/news-releases/royal-canin-academy-announces-advancements-to-digital-learning-platform-at-vmx-2025-302355575.html

Royal Canin. Our History. www.royalcanin.com. Accessed February 4, 2025. https://www.royalcanin.com/us/about-us/our-history

Articles

The platform can provide flexible and mobile learning for veterinary professionals

Royal Canin unveils revamped digital learning platform

Jason B. Pieper, DVM, MS, DACVD talks about what goes into the diagnostic process for atopic dermatitis

Diagnosing atopic dermatitis

The diagnostic process for atopic dermatitis—one of exclusion—can be challenging. In an interview with 

on his lectures presented at the 2025 Veterinary Meeting & Expo (VMX), Jason B. Pieper, DVM, MS, DACVD, assistant professor at Iowa State University, goes into detail about this process. In this video, Pieper discusses one of the first causes of pruritus that are usually ruled out first in the diagnostic process and talks about what should follow.

Below is a partial transcript which has been lightly edited for clarity.

Diagnosing atopic dermatitis is a matter of just ruling out all other causes of itching, which can be somewhat difficult at times. But one of the big things that we typically start to rule out is parasites, looking you know, whether it's fleas that could potentially be causing flea allergies. Also other parasites, like Demodex, scabies, things like that, that can cause pruritus, so that's a big one.

The other big ones we're always ruling out is infections. So secondary infections, whether it's bacteria, fungal, whether it's Malassezia or dermatophytes, those are other causes of pruritus.

Then we get to other kind of aspects of autoimmune diseases, keratinization disorders, endocrinopathies, that can also cause actually pruritus but then, you know, be kind of subsequent to that of causes. But once you rule out those, then the other aspect that becomes a little bit more difficult is ruling out food allergies. And once you rule out food allergies, you know, based on either clinical criteria or doing a good diet trial for them, then once you do that, you actually back yourself into a corner to say, ‘Yes, this dog has atopic dermatitis now,’ and you feel comfortable with that.

With food and environmental allergies or atopic dermatitis, you know, some of it can be ruled out honestly just from the history alone. If the animal is highly seasonal, that pretty much tells you it's not a food allergy, unless they [client is] feeding [them] something seasonal. So that's probably one of the things, just from the history alone, you can kind of rule out food allergies and make it easier on yourself as a you know, a veterinarian and a diagnostician.

Pinpointing atopic dermatitis in patients

Zoetis has updated the US label for Librela (bedinvetmab injection), following its submission of a supplement to the FDA, according to the company. The updated labeling is based on post-approval experience with Librela in the US since the product launched domestically in October 2023.

Librela is indicated for the control of pain associated with osteoarthritis (OA) in dogs. It is a once-monthly injectable monoclonal antibody that is administered by veterinary professionals.

“Pets are at the center of everything we do at Zoetis, and we are constantly working to support veterinarians and pet parents in ensuring they have the resources to make informed decisions for the animals in their care,” Richard Goldstein, DVM, DACVIM, DECVIM-CA, global chief medical officer and head of medical affairs for Zoetis, said in the release.

Label updates for pharmaceutical products are not uncommon, often occurring in the first few years after a launch and with real-world drug experience data gathered, according to Zoetis. The company has been working with the FDA to review real-world drug experience data and its own pharmacovigilance monitoring for safety and efficacy.

Adverse events with Librela have been reported by veterinarians and pet owners. In January 2025, the FDA alerted animal health professionals about adverse events in dogs treated with bedinvetmab injection, in a “Dear Veterinarian” letter listing neurologic signs as well as excessive thirst, urination and death.

In a public statement, Zoetis said the “Dear Veterinarian” letter was an informational update rather than a warning. “This agency review of reported adverse events is part of the FDA’s standard process following approval of any product. FDA’s communication to veterinarians is designed to inform and educate professionals and pet owners, supporting transparent and meaningful discussions about treatment decisions. The data shared with veterinarians by the FDA aligns with our own ongoing monitoring of Librela’s safety and efficacy. At Zoetis, we work closely with the FDA and other global regulatory agencies to provide context to reported events,” the statement noted.

In a recent letter about the Librela label updates sent to veterinarians and shared with 

, Goldstein noted there is no change to contraindications, warnings or precautions. However, this label update includes the addition of a client information sheet, a post-approval experience section, a section of information for dog owners, and a statement in the dosage and administration section regarding the client information sheet and potential adverse events.

The client information sheet includes medication information, monitoring guidelines and when to consult a veterinarian, according to the letter. The client information sheet is available on 

 and is being shared directly with veterinarians. The updated label and client information sheet will also be included in future distributions of the drug.

The company and Goldstein expressed continued confidence in the safety and effectiveness of Librela.

 “Every medicine has potential benefits and risks, and it’s important for pet owners to work closely with their veterinarians to weigh those appropriately and maintain an open dialogue about their pets’ experiences…We stand firmly behind Librela, and the positive impact it is having on dogs that suffer from osteoarthritis pain,” Goldstein said.

Since it was approved by the FDA in May 2023, the drug has been used to treat more than one million dogs in the US. The implementation of the label update will be immediate, according to Zoetis.

The product was first launched 4 years ago in Europe and nearly 25 million doses have since been distributed globally, according to Zoetis. In a release, the company has said no individual adverse event signs have been reported at a rate higher than “rare” under European Medicines Agency (EMA) standards, with less than 10 occurrences per 10,000 doses.

 have also stood by the drug’s safety and efficacy. Although some post-injection adverse effects such as itching, loss of appetite, and head tremors were reported in some cases, they saw no serious adverse effects in these patients, while quality of life was noticeably improved.

Zoetis is continuously providing veterinarians with resources that include data, research and access to leading OA experts, according to the company. More than 1000 medical education webinars have been hosted by Zoetis in the past year to support veterinarians’ knowledge and understanding of how to use its products. The company has also held frequent Librela ‘office hours’ with Goldstein to address questions from veterinarians, and has field veterinarians assigned to regions in the local markets it operates in to provide additional support.

Zoetis announces US label update for Librela (bedinvetmab injection), a treatment to control canine osteoarthritis (OA) pain. News release. Zoetis. February 4, 2025. Accessed February 4, 2025. 

https://investor.zoetis.com/news/news-details/2025/Zoetis-Announces-U.S.-Label-Update-for-Librela-bedinvetmab-injection-a-Treatment-to-Control-Canine-Osteoarthritis-OA-Pain-2025-iu22I1cCqp/default.aspx

Bautista-Alejandre A. FDA notifies veterinarians of adverse events linked to canine osteoarthritis treatment. 

. January 8, 2025. Accessed February 4, 2025. 

https://www.dvm360.com/view/fda-notifies-veterinarians-of-adverse-events-linked-to-osteoarthritis-treatment

Zoetis statement on the safety of Librela. Zoetis. December 18, 2024. Accessed February 4, 2025. 

https://news.zoetis.com/press-releases/press-release-details/2024/Zoetis-Statement-on-the-Safety-of-Librela/default.aspx

Coppock K, McCafferty C, Yankowicz S. Animal health company assures veterinarians that OA drugs are safe. 

. April 16, 2024. Accessed February 4, 2025. 

https://www.dvm360.com/view/animal-health-company-assures-veterinarians-that-oa-drugs-are-safe

Librela (bedinvetmab injection) is a monthly injectable monoclonal antibody, for which real-world drug experience data has been collected in the past year.

Drug label is updated for pain management therapy

Lindsay Starkey, DVM, PhD, DACVM (Parasitology) explains the common misconceptions pet owners can have about feline parasite prevention

interview with Dr Lindsay Starkey

According to the American Heartworm Society, only 5% of cats are on year-round heartworm disease prevention.

 Although there can be many reasons that these patients are not being given year-round heartworm disease prevention, one thing veterinary teams can do to help is discuss common misconceptions with clients. But what are they?

In this video with dvm360 prior to her lectures at the Veterinary Meeting & Expo (VMX), Lindsay Starkey, DVM, PhD, DACVM (Parasitology) shared the common misconceptions she hears when it comes to heartworm prevention in feline patients.

Linsday Starkey, DVM, PhD, DACVM (Parasitology): 

So there are a couple of big misconceptions about just vectors and vector control in general when it comes to cats, and they kind of center around the same thing, that the cat is at little to no risk for interactions with vectors because they live an indoor, or predominantly indoor, lifestyle, so fleas and mosquitoes and ticks can't come inside, therefore my cat is safe. Absolutely not true. I catch mosquitoes in my house routinely, and they can even bite through the screen window. If you have a cat that likes to sunbathe and press its body as closely to the outside as possible in that window, fleas obviously just reside indoors just fine. 

So if you get that infestation started, it could absolutely be a problem. In my own personal cat, when I was in veterinary school, [my cat] got a flea infestation because I got a dog and he was on good flea control, but [my] cat wasn't, and so [the] cat turned into the flea reservoir in the house. And then ticks too can hitch a ride indoors. Some ticks actually do survive indoors. And then that indoor only cat is rarely indoor only. They like to try to go outside and escape on you, or maybe they actually do have a Catio, or go on leash walks, or just get to go outside, but predominantly spend their time inside, and therefore the owner classifies them as indoor only because of the way we phrase that question. 

Take 5 on Feline Heartworm Disease. American Heartworm Society. Published 2025. Accessed February 3, 2025. https://www.heartwormsociety.org/resources/vet/infographics/632-take-5-on-feline-heartworm-disease

During this interview with dvm360, Lindsay Starkey, DVM, PhD, DACVM (Parasitology), shares some of the common misconceptions she hears surrounding feline heartworm prevention

Feline heartworm prevention misconceptions

Jen Sheehy, DVM, BCPA, discusses research on heartworm surveillance presented at the 2025 Veterinary Meeting & Expo.

Analyzing heartworm surveillance

Jenifer Sheehy, DVM, BCPA, medical lead, canine parasiticides at Zoetis, presented recent research on heartworm surveillance at the 2025 Veterinary Meeting & Expo (VMX), hosted by the North American Veterinary Community. She also discussed research insights from a new study in an interview with 

The following is a transcript of the video:

: With changes in micro climates, natural disasters, and dogs and cats being transported widely, we hope that more practices will be willing to participate in the future surveillance studies, not only for heartworm, but also for ticks and other vector borne diseases.

The biggest takeaway for us is that resistance is spreading geographically. The study found that resistant markers were as far north as Michigan, as far east as New Jersey, as far west as Kansas, and everywhere in between. So resistant isolates have now been identified quite a far distance from the Lower Mississippi River Valley, and in regions with endemic heartworm, every unprotected dog becomes a potential reservoir for resistance. 

I think it's really, really important that we all start to think of ourselves as shepherds for surveillance. This is a great opportunity for us to participate in the lessons that we can learn and in the information that we can share with each other.

Jenifer Sheehy, DVM, BCPA, presented new research on heartworm surveillance at the 2025 VMX event, and discussed study insights in an interview with dvm360.