A dairy farm in New York, milking 750 cows, in October 2024, experienced flea infestation in young calves. Seventy calves, fed a milk diet, were housed in individual hutches on gravel with chopped hay for bedding. Calves who were affected as early as 2 weeks of age presented with pruritis and alopecia. Four presumptive fleas were collected from a 3-month-old Jersey calf and submitted to the AHDC for parasite identification (PID). The fleas were confirmed as cat fleas, Ctenocephalides felis. Affected calves were treated with Ultraboss® (5% permethrin and 5% piperonyl butoxide), an insecticide labeled to kill lice and flies in cattle. There are no approved flea treatments for cattle in the US; permethrin, however, is reported to kill fleas.¹ Complete blood counts and chemistry panels on 9 affected calves were within normal limits.

One week later, AHDC veterinarians visited the farm and collected about 40 fleas from the same Jersey calf, which was the most severely affected, and had received 2 treatments with Ultraboss®, with the most recent treatment only 8 days prior. About 30 fleas were collected from a Holstein heifer calf in the neighboring hutch, and some more from younger calves. All fleas were Ctenocephalides felis. Minimal residual activity of permethrin-based products and constant reinfestation from the premises may undermine attempts at controlling flea scourge in calf hutches (personal communication with Dr. Michael Dryden, emeritus professor, Kansas State University).

Approximately 30 barn cats live on the farm and spend time near the youngstock. One cat spends time amongst the calf hutches, while others frequent the chopped hay bedding storage barn and the calving pen. It was not possible to catch and sample feral cats during the farm visit. The farm planned to treat all calves weekly with Ultraboss® for a total of five weeks, but did not plan to treat the feral cats or the environment for fleas. Note that permethrin is toxic to cats and premises can be treated with a pyrethroid product containing an Insect Growth Regulator (methoprene).

Flea infestations in dairy cattle in the U.S. is a rare occurrence, although feral cats are found on almost every dairy farm. An infestation was reported on a dairy farm in Kansas in 1993, with 3 calf deaths attributed to flea infestation and severe anemia (hematocrit 12-14%) in other calves. After combing one calf for a prolonged period, the authors counted 5,317 fleas.² To eradicate the fleas on this farm, all feral cats were removed, the calf barn was cleaned and sprayed with chlorpyrifos and methoprene, left empty, and then sprayed again in one month, and all calves were sprayed weekly with a pyrethrin and methoprene spray.² The flea lifecycle can vary from 2 weeks to more than 6 months, depending on the humidity and temperature,³ therefore continuous treatment of the animals and environment was required to eradicate a flea infestation in this setting.

Veterinarians who suspect flea infestation in cattle are encouraged to mail live fleas in a sealed container or Ziploc baggie to the AHDC and request parasite identification (test code PID).

References

1. Endris RG, Everett R, Cunningham J, Katz TL, Thompson K. Efficacy of two 65 % permethrin spot-on formulations against canine infestations of Ctenocephalides felis and Rhipicephalus sanguineus. Vet Ther. 2002 Fall;3(3):326-33. PMID: 12447841.
2. Dryden MW, Broce AB, Moore WE. Severe flea infestation in dairy calves. J Am Vet Med Assoc 1993;203:1448–1452.
3. Bowman DD. Georgis’ Parasitology for Veterinarians. Chapter 2: Arthropods. pages 38-9. 10th edition. Elsevier; 2014.