by David Rethorst, DVM, Veterinary Diagnostic Lab
Historically, anaplasmosis in Kansas has been diagnosed in the counties east of and including the I-35 corridor. The 2013 Disease Trend Map from the Kansas State Veterinary Diagnostic Laboratory (KSVDL) shows that anaplasmosis was diagnosed in 37 of the 51 counties in this area and only 8 of the 54 counties west of the I-35 corridor.
In 2015, the KSVDL map revealed that cattle infected with anaplasmosis were diagnosed in 45 of the 51 eastern counties and 24 of 54 counties west of the I-35 corridor. Three of the fifteen counties west of the I-35 corridor, yet east of and including the 281 corridor, had positive cases of anaplasmosis in 2013.
Yet in 2015, cattle infected with anaplasmosis were diagnosed in 13 of the 15 counties. Are there more cases of anaplasmosis creeping west in Kansas or are our improved diagnostic tools and our awareness of the disease helping us do a better job of finding this problem in our cows? Or is it a little bit of both? With cows being routinely hauled into and out of disease endemic areas on an annual basis for summer grazing and reports of strains of Anaplasma marginale that are resistant to chlortetracycline, one can see why the prevalence is increasing in Kansas.
Anaplasma marginale is a blood parasite that is spread by wood ticks, dog ticks, horse flies, deer flies, stable flies and fomites such as injection needles, tagging tools, tattoo pliers and other instruments that may be contaminated with blood. Cattle and the male wood tick are the primary reservoirs of the disease, with the organism multiplying in the salivary gland of the male wood tick. In Kansas, clinical signs of the disease are seen late summer through the fall months. These signs are the result of a marked anemia caused by A. marginale including open mouth breathing, staggering, and an aggressive attitude which are attributable to hypoxia created by the anemia. Other signs are yellow membranes of the eyes and vulva, abortion and death of mature cows. Death of mature cows during late summer and fall is one of the more common signs of anaplasmosis.
Many producers use chlortetracycline (CTC), a feed grade antibiotic, to prevent, control and treat anaplasmosis in their cows. In January 1, 2017 the Veterinary Feed Directive (VFD) that will go into effect will require a producer to have a VFD signed by their veterinarian and filed with their feed supplier before they can purchase CTC. Extra-label use of feed grade antibiotics will not be allowed and certainly will not be prescribed by a veterinarian in the VFD era.
Chlortetracycline is labeled for “the control of active infection of anaplasmosis.” Control, by Food and Drug Administration definition, means that signs of clinical disease are present in the herd and the antibiotic is being used to control the spread of disease to other animals in the herd. In the case of anaplasmosis, if CTC cannot be used until clinical signs of the disease are present, the producer is “behind the eight ball”. If the use of positive blood tests is allowed in order to document “active infection” and thus allow “control” strategies to begin would be a step in the right direction. At this point, we do not know if this will be allowed by FDA. Hopefully we will have a better idea after the Anaplasmosis Symposium being sponsored by Kansas State Research and Extension (KSRE) and the KSU College of Veterinary Medicine (KSU CVM) on May11, 2016 in Salina. For more information on the meeting or to register, contact Anthony Ruiz at firstname.lastname@example.org or 785-392-2147. Registration is due May 6, 2016. In some instances, there are questions about how is CTC delivered that hopefully can be clarified at the symposium.
Other strategies that can be utilized in the control of anaplasmosis include tick control, fly control and being diligent in avoiding the transfer of blood from animal to animal via needles, tattoo pliers and other instruments. Insecticide pour-ons can aid in the control of both ticks and flies. Reducing and eliminating potential breeding sites is necessary for proper fly control. Studies indicate pasture burning reduces tick numbers however, anecdotal reports following burning indicate that ticks are driven to the draws during burning.
A killed, provisional use anaplasmosis vaccine is currently being produced at Louisiana State University. This vaccine was a federally licensed product at one time but a change in marketing strategy by the sponsoring pharmaceutical company removed it from the market. The vaccine is reported to not prevent infection by A. marginale but will reduce the clinical signs of the disease. The use of this vaccine must be authorized by the state veterinarian. Once again, more questions that need to be answered.
As you can see, anaplasmosis is a growing concern in the state of Kansas. The disease is being reported in more counties than three years ago. There are questions about how we are going to be able to use CTC after January 1, 2017 as well as questions about use of the killed vaccine and how to control ticks and flies. Communicate with your veterinarian as you seek answers for your questions. KSRE and KSU CVM are both committed to helping the producers and veterinarians in the state of Kansas answer these questions.