Veterinarians might be the first line of defense in identifying New World screwworm (NWS) as the parasite re-emerges in the U.S. In a special episode of “The Bovine Vet Podcast,” Dr. Diane Kitchen, state epidemiologist with the Florida Department of Agriculture and Consumer Services, emphasizes rapid reporting and careful wound monitoring will be critical to limiting the impact of the disease. Dr. Kitchen was in Florida in 2016 during an incursion of NWS and has first hand experience with eradication of the pest.
“Early reporting is really the key to a rapid response. Any kind of delays in reporting can be very costly to our animals and to our industry,” she says.
Because suspicious lesions can be difficult to distinguish from other maggot infestations, Kitchen urges practitioners to err on the side of caution whenever larvae are found in living tissue on a live animal.
“I tell our practitioners I’d rather get a thousand cases that are not New World screwworm than miss one that is,” she says.
For veterinarians responding to potential cases, proper sample collection and follow-up treatment are essential components of the response effort.
NWS Sample Collection Protocol
When NWS is suspected, veterinarians should collect samples before beginning wound treatment whenever possible.
1. Photograph the wound before disturbing it.
Take clear photos of the lesion with larvae still in place. The distribution of larvae within the wound can help investigators determine the likelihood of a screwworm infestation and prioritize follow-up activities.
2. Collect larvae from multiple locations within the wound.
Do not limit sampling to larvae found on the surface. Collect specimens from deeper portions of the lesion as well, as different life stages may be present throughout the wound.
3. Collect multiple larvae of different sizes.
NWS passes through three larval stages while feeding within a wound. Collecting larvae of varying sizes increases the likelihood of obtaining diagnostically useful specimens.
4. Preserve samples properly.
Place collected larvae in a sealed container containing at least 70% alcohol to preserve them for laboratory examination.
5. Record the animal’s location.
Whenever possible, document the location where the animal was found, including GPS coordinates. This information can assist animal health officials with surveillance and response efforts.
6. Contact animal health officials.
Work with state animal health officials or USDA personnel to determine submission procedures, shipping requirements and any local collection points that may be available.
NWS Treatment Recommendations
Treatment begins with removing as many larvae as possible from the wound. However, removed larvae should not simply be discarded onto the ground. Instead, they should be destroyed using an approved insecticidal product to prevent further development.
Once larvae have been removed, wound management should proceed based on the severity of the lesion. Depending on the case, treatment may include topical therapies, systemic antibiotics, anti-inflammatory medications and pain control measures.
It is important to know a single appraisal is not sufficient. Additional larvae can remain hidden deep within the wound and might emerge after the initial treatment. As a result, affected wounds should be inspected daily until healing is well underway and no further larvae are observed.
Monitoring should not stop with the affected animal. Producers should carefully examine the remainder of the herd for additional wounds or suspicious infestations. Early identification of new cases can improve response efforts and help limit the spread of the parasite.
NWS infestations indicate the presence of flies in the area rather than direct animal-to-animal transmission. Any wound, including navels, castration sites, dehorning wounds, branding sites and other injuries can serve as an attractive location for egg deposition and should be monitored closely.
Vigilance Remains the Best Defense
While sterile fly release programs and other control efforts continue to expand, Kitchen stresses surveillance remains one of the most effective tools available to veterinarians and producers. Routine observation, prompt reporting and diligent wound management will remain critical as animal health officials work to contain and eliminate new infestations.
“Nothing replaces the close monitoring of individual animals,” Kitchen says. “I can’t stress the importance of that enough, getting out there and looking at animals.”
For practitioners in affected and at-risk areas, that simple advice may be one of the most important tools available in the fight against NWS.
To hear more from Dr. Kitchen on New World screwworm, tune in to the latest episode of The Bovine Vet Podcast:
