Australian veterinary parasitologist Dr. Matthew Playford is sharing with U.S. cattle producers what his country has done to raise awareness of potential, serious infection transmitted by the Asian longhorned tick (ALT).
In endemic areas of Australia where ticks are commonly found, almost all cattle are exposed to ticks from a very early age and get Theileriosis while young. “They start to show poor health at around two months of age,” he said. “That can be matched to their packed cell volume. Animals in endemic areas are born with normal blood parameters, then the packed cell volume starts to decrease and reaches its lowest point between two and four months of age.” Infected animals have slight anemia, slow growth rates and are highly susceptible to diseases such as pneumonia, coccidiosis, pinkeye and other calfhood illnesses. Affected animals also lose weight. Some endemic areas have recorded up to 10% mortality rate.
“It isn’t all bad news,” said Playford. “We have opportunities for Asian longhorned tick and Theileriosis control, and it revolves around five things: managing pastures, using tickicides, care when transporting cattle, monitoring introduced cattle and nutrition and nursing care for calves.”
Pasture management involves keeping cattle in a dry lot where they’re provided with hay and feed. “It’s almost impossible to imagine these cattle getting ticks or Theileriosis because it isn’t good habitat for ticks,” said Playford. “But ticks thrive, especially if there are incursions of wildlife carrying them, right up to tree edges and brush. Cattle adjacent to those areas are most at risk.”
Managing pastures and keeping the most vulnerable cattle away from wooded areas frequented by wildlife and pastures with a lot of dry matter will help modulate the dose of Theileria cattle get – ideally, a non-fatal dose. “In Australia, cattle that get one or two ticks and get a small dose of Theileria will most likely survive and become immune,” said Playford. “Cattle that get dozens or hundreds of ticks … are more likely to succumb.”
Keeping grass short helps reduce tick survival on pasture. Eliminating grazing cattle on certain pastures will not help manage ALT populations because the tick can survive for many months without feeding. In addition, the presence of wildlife on ungrazed pastures will help support tick survival.
Playford described the use of tickicides and cautioned American cattle producers to use products in accordance with label instructions. “The most commonly used products are synthetic pyrethroids,” he said. “They claim to protect for up to 10 days and are effective at killing ticks. Because this is a three-host tick, no resistance has been detected in Australia.” He said a pour-on formulation of Flumethrin will provide between three and six weeks of protection depending on infection pressure.
Organophosphates such as chlorfenvinphos and cypermethrin keep ticks off cattle for about 14 days. Another product, amitraz, is effective at killing ticks but doesn’t have any residual effect so ticks can reinfest cattle shortly after it’s applied.
“The most popular products in Australia for internal and external parasites are the mectins, particularly Cydectin® pour-on and Dectomax® injectable,” said Playford. “They’re quite effective but do not have label claims for Asian longhorned ticks. We’re just piggybacking their use from established claims for cattle fever ticks.” He suggested cattle producers use acaricide tick control to prevent tick buildup on cattle, with product selection based on what works in a particular area.
Moving cattle is problematic because most outbreaks are found in transported cattle. “Cattle fall into two groups: Naïve cattle that have never been exposed to Theileria because they live in an area where there aren’t many ticks. That would be the case for a lot of beef cattle in the U.S.,” said Playford. “Then we have cattle in endemic areas that are exposed to the disease at a young age and are unlikely to develop clinical disease.”
Cattle transported from tick-infested areas to tick-free destinations can put tick-free cattle at risk.
Transported cattle should be monitored carefully for signs of illness. Playford said cattle can go downhill quickly any time between two weeks post-introduction to several months later. Cattle close to calving, which is metabolically stressful, are at high risk of disease in tick-infested areas. Calves are susceptible in areas when there is seasonal pressure when ticks are at high levels.
Calves that have not had previous exposure and have little or no immunity should be pastured where tick populations are low. When cattlemen introduce new cattle to their farms, Playford suggested checking the history of the farm of origin.
“Manage calves carefully during the critical two- to six-month age bracket,” said Playford. “Treat all introductions, and quarantine cattle you’re bringing in. Make the best use of veterinarians and laboratories for diagnostics and develop biosecurity plans.”
by Sally Colby