by Sally Colby
Most horse owners will say they don’t recall ticks being a problem on their horses 10 to 15 years ago, but these freeloaders are increasingly responsible for transmitting serious diseases to both humans and horses.
Dr. Ericka Machtinger, assistant professor of entomology at Penn State University, said tick ecology isn’t well studied, but the risk of tick bites is increasing. “In a 2018 study, the CDC compiled 13 years of data and stated that there has been a tripling of vector-borne disease in the United States over those 13 years,” she said. “Ticks, mosquitoes and fleas are primary vectors in the United States, and the pathogens they transmit have become more common.”
The northeastern part of the country is rife with Lyme disease, and cases of two other tick-borne diseases – anaplasmosis and babesiosis – are on the rise. “Lyme disease cases are seen predominantly in heavily wooded areas,” said Machtinger, noting that many Lyme cases are seen in and near state forests. “But even outside those areas, there is risk of infection.”
Tick problems aren’t limited to pastured horses or those used for trail riding. “Any time we are outside, we’re potentially at risk for tick-borne diseases from tick bites,” said Machtinger. “That has a lot to do with the ecology of the tick – where they are and the host they bite.”
It’s important for realize that ticks are everywhere, and even though there are about 20 tick species in the northeast, only a few are of concern to horse owners. The challenge in identifying ticks is that their appearance varies according not only by species, but also life stage and the extent of a blood meal they’ve consumed.
“The most common tick associated with pathogens is the black-legged tick (Ixodes), also called the deer tick,” said Machtinger. “This is the one you’ll see most frequently on yourself, dogs and occasionally on horses.”
The female black-legged tick has a red abdomen with a dark scutum, or shield, on its back; the male is dark brown. “The key characteristic with black-legged ticks is that they’re very small, one of the smallest tick species, but have an elongated shape,” said Machtinger. “The nymphs are also very elongated, and are extremely small. That’s why they’re such a concern for us – they’re the Lyme disease vector, and they’re so small it can be difficult to see them.”
The American dog tick is often found on pastured animals, and adults are easy to identify because they have ‘ornamentation’ that gives them a painted appearance. “Male American dog ticks have all-over coloration on their backs,” said Machtinger. “Females are a darker reddish brown and have an elongated shape similar to the black-legged tick. These ticks are really big, and it’s obvious they’re different from black-legged ticks.”
Two other potentially harmful tick species are the Lone Star tick, which is more frequently found in southern Pennsylvania, Maryland and Virginia, and the brown dog tick, which has a wide range but most common in southern states.
Machtinger discussed a relatively new tick arrival, the Asian longhorned tick. This tick is originally from Asia, was first found in New Jersey in 2017 and has now been found in Pennsylvania, Virginia, West Virginia, New York, Connecticut, North Carolina and Arkansas. One concern with this tick is that it’s parthenogenic – it can reproduce without a male. Machtinger describes this tick as boring brown, making it more difficult to identify, but some state universities accept samples for identification.
Understanding tick biology is important in both identifying ticks and predicting highest activity levels. In short, adult females lay eggs in spring and eggs hatch in late summer. The larvae are not infected with diseases, but if the larval tick bites an infected mammal, it may pick up that pathogen and become infective. The tick drops off the animal, molts to nymph and overwinters. The following spring, that infective nymph may infect humans, horses, dogs or other mammals. Nymphs can become carriers after biting an infected animal, which is why tick infection rates range from 30% to 80%.
The American dog tick has somewhat different seasonality. Adult American dog ticks are the species most often found on horses; usually around the chest, under the jaw and around the ears from spring through late summer. Nymphs are common from mid-summer through early fall, and larvae are present year round.
Limiting ticks around the farm is possible, primarily through landscape management to eliminate host habitat. Machtinger said black legged tick populations can be reduced by up to 100% just by removing leaf litter. Rock walls and fallen vegetation harbor small mammals, so eliminating those can help. “Instead of having pastures that border vegetation, have a nine foot or greater path around the pasture can help reduce the ability of ticks to get to the edge of the fenceline where they can seek hosts,” said Machtinger. “Keep grass cut short, open the space and leaf litter removed. Ticks are susceptible to drying out, so if you can keep grass low and take away places where they can hide and stay wet, there’s a better chance of reducing tick numbers around pastures.”
Biocontrol is another tick management method, and one option is a naturally occurring fungus that can kill ticks with minimal applications. The product is compatible with beneficial arthropods such as pollinators. “There are concerns that it can be tricky to purchase, and it is not compatible with aquatic wildlife,” said Machtinger. “If you’re near a stream or pond, be careful because it’s toxic to fish.”
Chemical applications are an option for heavily infested areas. In most cases, two applications will be sufficient. Be sure to check the product label and use according to labeled instructions. Chemical applications are proven to be effective in significantly reducing tick populations, but can be toxic to beneficial arthropods and aquatic life.
Host-targeted control helps to minimize ticks on small mammals such as chipmunks and mice. This method is most effective when used in conjunction with other methods. Results are variable.
There’s evidence that free-range fowl can help manage tick populations. Machtinger said a graduate student in Virginia conducted research and found that although guinea hens eat ticks. ticks also got on the guinea hens – so did the birds eat enough ticks to be useful?
Horse owners should check themselves and their animals at least once a day for ticks, especially after outdoor exposure or trail riding. Prompt removal of ticks can prevent costly and debilitating disease.
For more detailed information on tick species and control, visit tickencounter.org