Ask the Vet: What can we do about the new tick in the Northeast, the Asian Longhorned Tick?

By Dayna Locitzer, DVM

Unfortunately there is a new tick in town, the Asian Longhorned Tick (ALT). Originally from east Asia, ALT was first identified in the United States in 2017 but likely has been here since 2010. It can now be found in over 22 states with the highest prevalence in Virginia and surrounding areas. In the northeast, it has been found mainly in eastern and southern New York, but also reported in isolated locations in Massachusetts, Connecticut, Rhode Island, New Hampshire and Maine. But, its geographic reach is likely to expand due to a number of factors including climate and habitat change as well as the movement of animals. ALT carries the disease called Theileriosis, caused by the blood-borne protozoal parasite Theileria orientalis. Organic dairy cows have a high level of tick exposure due to the time they spend on pasture and the lack of insecticides used, making it important to be aware of ALT and Theileriosis.

ALT is a particularly insidious bug because of how it reproduces. It asexually reproduces, therefore a single female can create a significant infestation. Oftentimes you will see patches of skin that are covered in ticks, which sets it apart from other tick species. (PICTURE 1) Like other ticks they prefer tall grasses and wooded areas and can travel on wild birds. ALT is the carrier for Theileria orientalis, but not all ALT carry it.

Theileria orientalis is the causative agent of Theileriosis, is a protozoa. This means it’s a little more sophisticated than bacteria. Theileria orientalis lives in the bloodstream and can attack red blood cells, destroying them, leading to severe jaundice and anemia. Clinical signs of this type of anemia are weakness, weight loss, yellow mucous membranes, general lethargy, all due to the destruction of the red blood cells. This disease can only be treated with a blood transfusion and supportive care, no pharmaceuticals approved in the United States are known to be effective against Theileriosis.

I’ve told you lots of bad news, now for the good news- clinical cases of Theileriosis are rare, and even rarer are the severe cases. Many animals will be infected, but only few will show signs of disease. Clinical disease will potentially occur when an animal is first exposed to Theileria orientalis and is more likely to cause issues in younger animals or animals in stressful circumstances. Once an animal is positive for Theileria orientalis, they have it for life. While that doesn’t sound like a positive, it is because once they have it, they can’t get it again!

So, what should you do with all this information?

1. Look at the attached map and see if your farm is in an area where ALT has been identified (Picture 2)
2. Look out for the ticks on your farm and notify your veterinarian if you see them
3. If you have an animal that is showing signs of anemia, have your veterinarian test for Theileriosis in addition to other diseases
4. If you are in an ALT positive area, you might want to sample a handful of your cows to see if the disease is already in your herd
5. When introducing new animals to your herd, follow the below chart for guidelines related to Theileriosis
6. Change needles in between each animal when giving injections. Because it is a blood-borne pathogen, Theileriosis can be transferred with shared needles

To prevent severe infestations on your dairy herd, utilize similar strategies that you use for fly prevention like rotating paddocks regularly, clipping pastures, essential oil sprays, and mineral supplements that deter biting insects. Inspect your youngstock regularly for ticks, and if possible remove the ticks and deposit them in alcohol to kill them. Those killed ticks can then be submitted to your veterinarian for testing.

This is an emerging pest and disease in the northeastern United States and there will continue to be new information released, look out for it!

Your Herd Status	Purchased Animal Status	Risk Level
Negative	Negative	Safe
Positive	Positive	Safe
Negative	Positive	Increased Risk Established herd at risk if Asian Longhorn Tick are present on farm Take steps to protect your herd with increased tick protection and single use needles Monitor herd for transmission through testing Observe for signs of illness related to Theileria
Positive	Negative	Increased Risk Purchased animal(s) at risk Take steps to protect purchased animal(s) from contracting Theileria during times of stress Isolate purchased animal(s) for 2 weeks upon arrival Use effective tick protection while being introduced to herd Observe purchased animal(s) for signs of illness related to Theileria

Image 1. Asian Longhorned
tick infestation on the ear of
beef Steer in Catskill, NY:

Posted: to Organic Production on Sat, Jul 4, 2026
Updated: Sat, Jul 4, 2026