Written by Aileen Thompson, DVM
Veterinarians play a unique role in protecting both animal and human health. Many diseases affecting animals have the potential to impact people, livestock, wildlife, and entire communities. Through disease surveillance, preventive medicine, and public education, veterinarians are often among the first to identify emerging health threats.
Two infectious disease concerns currently receiving significant attention are the re-emergence of New World Screwworm in the United States and the identification of a newly recognized tick-borne rickettsial disease in Northern California. While these diseases are very different, both highlight the importance of vigilance, prevention, and the interconnected nature of animal and human health.
New World Screwworm: A Parasite Returns to the United States
One of the most significant veterinary public health developments of 2026 has been the return of New World Screwworm (Cochliomyia hominivorax) to the United States.
For decades, New World Screwworm was considered eradicated from the U.S. through an extensive federal control program. However, after spreading northward through Central America and Mexico, confirmed cases have now been identified in both Texas and New Mexico. These cases have involved livestock as well as a dog, demonstrating that the parasite can affect both agricultural animals and companion animals.
The detection of New World Screwworm in the United States marks the first confirmed U.S. cases in approximately sixty years and has prompted a significant response from federal and state animal health officials.
What Is New World Screwworm?
New World Screwworm is a parasitic fly whose larvae feed on living tissue.
Unlike common maggots, which generally consume dead tissue, screwworm larvae actively invade healthy tissue and burrow deeper as they grow. This behavior can result in rapidly progressive and painful wounds.
Adult flies are attracted to:
- Open wounds
- Surgical incisions
- Bite wounds
- Skin infections
- The ears, eyes, nose, mouth, and other body openings
After eggs are deposited, the larvae hatch and begin feeding on healthy tissue. Without treatment, wounds can become extensive within days.
Which Animals Are at Risk?
New World Screwworm can affect:
- Dogs
- Cats
- Horses
- Cattle
- Sheep and goats
- Wildlife
- Humans in rare circumstances
Because the larvae consume living tissue, infestations can cause severe pain, secondary infections, tissue destruction, and even death if left untreated.
Why Pet Owners Should Be Concerned
Although much of the focus has been on livestock, companion animals are also susceptible. A recently confirmed case involving a dog highlights that pets are not immune to infection.
Pet owners should carefully monitor any wounds, surgical sites, or skin lesions and seek veterinary care if they notice:
- A wound that rapidly worsens
- Foul odor or discharge
- Swelling around a wound
- Visible larvae or maggots
- Persistent pain or irritation
Early diagnosis and treatment are critical.
Travel Considerations
The spread of New World Screwworm has resulted in increased surveillance and movement restrictions involving animals traveling across the U.S.-Mexico border.
At the time of writing, restrictions and additional requirements are in place for many animals crossing from Mexico into the United States. Pet owners planning international travel should verify the latest requirements well in advance of their trip, as regulations may change rapidly in response to disease outbreaks.
Veterinarians issuing health certificates should remain aware of evolving regulations and screening requirements related to New World Screwworm prevention.
What Is Being Done?
Fortunately, animal health officials have successfully battled this parasite before. Federal agencies are deploying surveillance, containment measures, and sterile-fly control programs similar to those used during the original eradication effort.
While the situation remains concerning, there is optimism that rapid intervention can prevent widespread establishment of the parasite within the United States.
Emerging Tick-Borne Diseases in California
Ticks remain one of the most important disease vectors affecting both animals and people. Most Californians are familiar with Lyme disease, but researchers continue to discover additional pathogens carried by ticks throughout the western United States.
Recently, scientists identified a newly recognized rickettsial disease in Northern California. This bacterium belongs to the same family of organisms responsible for Rocky Mountain spotted fever, one of the most serious tick-borne diseases in North America.
Although human infections remain rare, the discovery serves as a reminder that new pathogens continue to emerge and that our understanding of tick-borne diseases is constantly evolving.
What Are Rickettsial Diseases?
Rickettsial diseases are caused by bacteria that are typically transmitted through tick bites.
In people, these infections may cause:
- Fever
- Headache
- Fatigue
- Muscle aches
- Rash
- Neurologic symptoms in severe cases
Many rickettsial diseases respond well to treatment when recognized early, but delayed diagnosis can result in serious complications.
Why This Matters for Pet Owners
Dogs and cats often serve as sentinels for environmental health risks. Pets frequently encounter ticks during outdoor activities and may bring ticks into the home, increasing opportunities for human exposure.
While pets may not always develop the same illnesses as people, effective tick prevention helps protect both animal and human family members.
The emergence of new tick-borne pathogens reinforces the importance of year-round parasite prevention, even in regions where tick-borne disease has historically been considered uncommon.
Tick Prevention Strategies
Pet owners can reduce risk by:
- Using veterinarian-recommended flea and tick preventives year-round
- Checking pets for ticks after hiking, camping, or outdoor activities
- Keeping grass and vegetation trimmed around the home
- Removing attached ticks promptly and properly
- Scheduling regular wellness examinations
Consistent tick prevention remains one of the most effective tools for reducing disease risk.
The One Health Connection
Veterinarians often refer to the concept of One Health, which recognizes that the health of people, animals, and the environment are closely interconnected.
The return of New World Screwworm and the discovery of emerging tick-borne pathogens illustrate why disease surveillance is so important. Many public health threats are first identified through monitoring wildlife, livestock, companion animals, or environmental changes.
By staying informed, maintaining preventive veterinary care, and working closely with public health and medical professionals, we can help protect both animals and people from emerging infectious diseases.
While new health threats will continue to emerge, awareness, prevention, and early intervention remain some of our most powerful tools. Keeping pets current on wellness care, parasite prevention, and routine examinations not only protects them—it helps safeguard the health of our entire community.