A few years ago, many cattle producers in the Heartland had never heard of anaplasmosis. But now, when Kansas State University Extension planned a one-day seminar on the cattle disease, registration quickly exceeded the facility’s seating capacity, and the organizers added a webcast of the event to accommodate interested ranchers from Kansas and other states. The event, which took place in mid-May, attracted 164 live attendees and another 70 joined online.
Anaplasmosis, generally associated with the bacteria Anaplasma marginale, is a tick-vectored disease that, in the past, has been most prevalent in the Gulf Coast region and other humid environments. Flies also can pass the disease by mechanical means by carrying infected red blood cells between cattle.
More recently though, anaplasmosis has appeared and caused economic losses in beef and dairy herds around the country, including the Midwest and arid West.
“In 2015, almost every county in the eastern two-thirds and several far-west counties of Kansas had samples that were tested and found to be anaplasmosis positive,” says Gregg Hanzlicek, DVM, PhD, director of production animal field investigations for the Veterinary Diagnostic Lab, noting that it’s not unusual for the disease to be found in eastern Kansas but had not been so much a problem in western Kansas until recently.
“We don’t know if the geography of this disease has changed or if veterinarians and producers are looking harder for it, but it is clear that there are positive herds in a very large percentage of Kansas.”
Hanzlicek says clinical signs, in adult cattle older than two years, tend to appear within six to 70 days following infection, with an average of 28 days. Clinical signs include:
· Adult cows or bulls found dead in the pasture
· Difficulty breathing (especially when moved)
· Aggressive behavior
· Icterus or jaundice, characterized by yellow membranes in the eye related to an enlarged spleen
· Weight loss
Infection occurs through blood transfer, typically from ticks, flies or “fomites” such as needles used on multiple animals. All ages of cattle can become infected, with younger animals tending to be more resistant to infection than adults.
All recovered animals will remain lifelong carriers, which do not experience clinical disease but can serve as a source of infection for insect vectors, Hanzlicek says.
Anaplasmosis, Hanzlicek says, is not:
· A typical bacterial disease. It is a Rickettsia disease, with a very narrow choice for therapy, in which the pathogen must parasitize red blood cells to survive.
· A uniform disease caused by a consistent parasite. There are different serotypes which originated from different areas of the country. Research tells us, Hanzlicek says, that the ability to cause disease and the response to therapy may be quite different for the different serotypes.
· A disease that goes away if the animal survives clinical disease.
· A disease with different clinical outcomes based on the age of cattle infected.
· A disease that can be spread in multiple ways. Ticks serve as hosts, with the male tick acting as a carrier in which the disease replicates. Flies also can pass the disease by mechanical means through carrying infected red blood cells between cattle. We can spread the disease through fomites such as injection needles, dehorners, and implant needles.
· A disease for which some of our thinking has been informed by older studies that used relatively insensitive tests.
· A disease with limited data related to the efficacy of treatment and control programs.
Controlling the disease begins with biosecurity – using testing and quarantine to avoid introducing infected animals into herds, insect-control efforts, vaccination, ongoing testing and use of feed-grade chlortetracycline (CTC) for treatment and control, particularly during the vector season.
A vaccine is available for provisional use in many states and has demonstrated efficacy in reducing clinical signs of anaplasmosis. The killed vaccine requires two doses the first year and one dose in subsequent years.
Veterinarians remind producers that use of feed-grade CTC, beginning in January 2017, will require veterinary oversight within the context of a valid veterinarian-client-patient relationship. Full implementation of the FDA’s new veterinary feed directive (VFD) rule will end over-the-counter (OTC) sales of medically important antibiotics used in feeds.
Watch for more detailed articles on anaplasmosis in the upcoming issues of Drovers and Bovine Veterinarian.