Full Breakdown
FDA Approves New Treatment for Screwworm and Cattle Fever Tick
12/9/2025, 11:10:12 PM
Conditional Approval of Exzolt Cattle-CA1
The U.S. Food and Drug Administration (FDA) has granted conditional approval for Exzolt Cattle-CA1, a topical solution developed by Merck Animal Health, aimed at preventing and treating New World Screwworm (NWS) infestations and controlling cattle fever tick in beef cattle aged two months and older, as well as replacement dairy heifers under 20 months. This approval comes as U.S. cattle ranchers face significant threats from these parasites, particularly as the screwworm has been decimating cattle populations in Mexico.
The FDA's decision allows farmers to access Exzolt Cattle-CA1 starting December 20, 2024, through their veterinarians. The drug is designed to be applied directly to the cattle's skin and is effective for 21 days, with a 98-day withdrawal period to ensure no drug residues remain in meat. FDA Commissioner Marty Makary emphasized the importance of this approval, stating, “This conditional approval gives cattle producers a new tool to combat two parasites threatening the well-being of cattle in the U.S.”
Background on Screwworm and Cattle Fever Tick
The New World Screwworm is a parasitic fly that lays its eggs in open wounds of livestock, leading to severe infestations and often death if untreated. Although NWS has not been detected in the U.S., the cattle fever tick is present and poses a significant risk to cattle health. The FDA noted that the conditional approval of Exzolt Cattle-CA1 is a response to the urgent need for effective treatments against these parasites, especially given the complex nature of demonstrating the drug's effectiveness.
Implications for Cattle Producers
The introduction of Exzolt Cattle-CA1 represents a critical advancement in the fight against these parasites. However, Holger Lehmann, vice president of pharmaceutical research and development for Merck Animal Health, cautioned that the drug alone cannot quickly eradicate the screwworm problem, indicating that it may take several years to resolve the issue fully. The FDA has also highlighted that antiparasitic drugs should only be used when medically necessary and as part of a comprehensive parasite management strategy.
Criticism and Concerns
While the approval of Exzolt Cattle-CA1 is seen as a positive step, there are concerns regarding the long-term effectiveness of the treatment and the potential for developing resistance among parasites. Critics argue that reliance on a single drug may not be sufficient to address the widespread issues posed by screwworm and cattle fever tick infestations.
Verbatim Quotes
- “This conditional approval gives cattle producers a new tool to combat two parasites threatening the well-being of cattle in the U.S.,” — Marty Makary, FDA Commissioner.
- “Experts tell us in Mexico that they don't expect that they're going to be able to get rid of the screwworm problem quickly,” — Holger Lehmann, Merck Animal Health.
The conditional approval of Exzolt Cattle-CA1 marks a significant development in cattle health management, providing producers with a new option to combat the threats posed by screwworm and cattle fever tick. However, ongoing monitoring and comprehensive management strategies will be essential to ensure the long-term health of cattle herds.
