WEST LAFAYETTE, Ind. — The number of leptospirosis cases diagnosed in dogs has nearly doubled compared to previous decades, according to a recent report.

Leptospirosis is a potentially fatal bacterial infection that all mammals – including humans, dogs, cattle and pigs – can contract. A recent report based on findings from veterinary schools across the United States shows an increased incidence in dogs, especially those living in urban areas, said Dr. George Moore, professor of epidemiology and small animal internal medicine at Purdue University.

The Midwest is at higher risk than other areas because of its high population of infected wildlife, such as raccoons, rats or deer, which spread the disease through their urine, Moore said. Standing water in ponds or puddles can become infected with diseased urine, especially after heavy rain or flooding, he added.

Animals who drink from these infected waters or come into contact with diseased wildlife are most at risk for leptospirosis; however, even smaller dogs who venture outside less are becoming infected more often due to increasing numbers of wildlife entering urban areas, Moore said.

"Leptospirosis appeared to decline in the 1980s, so vets or pet owners elected to not vaccinate their dogs. This resurgence is due to a lack of prevention in dogs," he explained.

Other animals most at risk include cattle, swine and horses. The disease causes abortions in cattle and swine. In horses, the most common manifestation is recurrent "moon blindness," or recurrent uveitis of the eye, according to the University of Wisconsin School of Veterinary Medicine.

The best offensive is to vaccinate animals against this disease annually, Moore said, although there is no vaccine for horses. Cats are rarely diagnosed with the infection, he added.

Leptospirosis may be difficult to diagnose properly in cattle, said Dr. Marc Caldwell, a specialist in farm animal field service and food animal internal medicine at the University of Tennessee.

"A farmer might know their cattle are infected if they are aborting mid-gestation. Dairy cows manifest with ‘milk drop syndrome,’ a drastic drop in milk production, for example 90 pounds to 40 pounds," Caldwell said.

Clinical tests are the best way to detect leptospirosis in suspicious cases, he added. Aggressive antibiotics can be used to stop the progression of serious infection, which can feature kidney and liver failure, abortions and ultimately death.

"Most of the time the biggest economic factor for farmers is abortion, the loss of calves and the loss of productivity in dairy cows. Unless the farmer is paying a lot of attention, it may go unnoticed," Caldwell added.

"Dogs are more severely affected by lepto. It induces severe illness ... There is the potential of infection for any mammal, but those in the backyard or pasture-raised are most at risk."

He recommends vaccination for all cattle and for pasture-raised pigs.

Humans can acquire the disease through contact with bodily fluids from sick animals, although the incidence is low, Moore said. Water sports in contaminated freshwater is another way humans can acquire leptospirosis, and that incidence is rising, according to the Centers for Disease Control and Prevention (CDC).

Caldwell, however, believes there is little risk of human infection from creeks, reservoirs, ponds or lakes. While the general public is not at great risk, farmers, veterinarians and vet technicians are more likely to come into contact with leptospirosis.

"The highest risk is from working with sick animals directly," he said. "Farmers should be careful any time they are caring for a cow that is aborting because there could be multiple pathogens transmitted from the aborted fetus. They should wear gloves and present the fetus for diagnosis, identifying to lab personnel that it could be a ‘lepto’ case."

With proper care in dealing with sick animals, there is a low risk of transmission to humans, Caldwell added.

In humans, males are more than twice as likely to be diagnosed than females, possibly because of increased exposure, according to a study by the CDC. Early symptoms in humans and animals are fever, headache, chills, muscle aches, vomiting, jaundice, anemia and sometimes a rash, with an average incubation period of seven days. These symptoms are easy to dismiss or misdiagnose, Moore said.

He said two vets on the same street may have different statistics on how many leptospirosis cases there are because testing for it is uncommon. Peak incidence of infection in the United States is late fall, according to VCA Antech, Inc.

Because of concerns of rising incidence nationally, the CDC reinstated lepto-spirosis as a reportable disease in 2013 in order to keep better records of its spread. An estimated 100-200 human cases are identified annually in the United States, with 50 percent of cases in Hawaii.

According to CDC, although incidence in the U.S. is low, leptospirosis is considered the world’s most widespread zoonotic disease, which is a disease that is transmissible from animals to humans.

The largest recorded U.S. outbreak was in 1998, when 775 people were exposed and 110 became infected after a water sport event at Lake Springfield in Illinois.

In 2014, a rise in infection of dogs was reported in Florida, according to news outlets. Travelers to Hawaii and Puerto Rico were advised by the CDC to take preventive measures earlier this year due to outbreaks of the disease. In recent years Nicaragua and the Philippines experienced a spike in human cases after severe flooding. Vaccination of dogs, cattle and pigs is highly recommended, Moore said: "Leptospirosis should be in the standard vaccination protocol of all breeding cattle and swine."