Texas FeverIt was the mid-19th century. The cattle drive era was in full swing, and longhorns from Texas were entering Kansas in droves on their way up to the railheads. New towns were booming and fresh beef was being supplied to industrialized, post–Civil War consumers. But something was seriously wrong.

The problem was not with the hardy longhorns themselves, but with the other breeds of cattle grazing in Kansas pastures. They were suddenly falling prey to a strange disease which caused anemia, high fevers, red urine, and severe lethargy, soon followed by death. What could be the matter?

Someone somewhere eventually realized that the disease only occurred in cattle who mingled with longhorns or who grazed pastures recently vacated by them. So the longhorns were to blame! No one could fathom how or why the healthy-looking longhorns were passing along the fatal disease, soon called Texas fever, to other breeds of cattle, but one thing was for certain: it had to be stopped.

Indignant citizens began meeting the herds with guns as they approached. Quarantines protected populated areas, but it was not enough. In 1885, Kansas prohibited Texas cattle from crossing the state lines, thus barring the herds from key railheads and effectively ending an already dying cattle drive era. Yet the disease still raged on, and no one knew why.

 

Unraveling the Mystery of Texas Fever

However, the disease-causing properties of bacteria were by this time becoming more widely known and acknowledged. Louis Pasteur had made strides in combating intractable diseases such as anthrax and chicken cholera over the past few decades. Inspired by his work, scientists set to work searching for the microorganism that was to blame.

In 1893, Theobald Smith and Fred Lucius Kilborne of the Bureau of Animal Industry in Washington, D.C., announced that they had discovered the organism responsible for Texas fever. Pyrosoma bigeminum, as they called it, was a microscopic protozoan that inhabited red blood cells and caused the disease.

Texas Fever

Cattle being treated for ticks

Furthermore, the protozoan was carried by ticks. A tick received Pyrosoma bigeminum by sucking on a longhorn carrying the protozoan. After engorging itself with infected blood, the tick dropped off into the grass to lay eggs. The new ticks carried the protozoan from the day they hatched, and whenever they bit another animal, they passed the microorganism on to their host and gave it Texas fever.

There were several aspects of Texas fever not understood at the time. For starters, there are actually two protozoans responsible for the disease in North America—Babesia bovis and Babesia bigemina. Accordingly, Texas fever is now called babesiosis.

Furthermore, we now understand better how it was that longhorns could carry the disease without any ill effects. Calves are born with a certain level of resistance to babesiosis that lasts for a month or two. A calf born in Texas in the late 1800s was quite likely to be bitten by an infected tick shortly after birth and would contract a mild form of the disease. However, the calf’s natural immunity would adapt to the presence of the protozoans and it would remain a carrier the rest of its life, although it would never appear to have babesiosis.

 

Eradicating Texas Fever

Quarantines were the first step in eradicating Texas fever from the United States, and vaccines were developed, but experts believe it was regular use of tick dips that did the job. In 1943, the federal government declared that Texas fever was eradicated from the country.

Today, the protozoans responsible for babesiosis are endemic to Mexico, with an estimated 60% of Mexican beef calves being exposed. In the United States, the protozoans can only be found in a buffer zone along the border, which has been quarantined since 1938. However, white-tailed deer can carry the responsible tick, and recent reports indicate that they along with stray cattle are carrying it right out of the quarantine zone. Furthermore, growing resistance to pesticides among ticks has made keeping the disease under control an increasingly knotty problem.

The USDA has hired “tick riders” to ride the border in search of stray cattle, which the inspectors rope and return to the quarantine zone. In November 2018, the USDA also announced plans to protect the buffer zone with eight-foot-tall wildlife fencing.

The mortality rate among adult cattle that were not exposed to babesiosis parasites as calves is estimated somewhere between 70% and 90%. Should bovine babesiosis ever manage to re-enter the American South, it could present a serious problem for cattle owners, as the immune systems of American cattle today are completely unequipped to deal with the parasite.

Posted by hsotr