science

Illustration by Aneri Pandya

Long dormant, leptospirosis experiences an outbreak in local canine populations

When we think about sharing things with man’s best friend, bacterial diseases are seldom the first that come to mind.

Although it has been centuries since it caused a large-scale human epidemic, leptospirosis, also known as Weil’s disease, has recently been on the rise in dog populations in Gainesville, infecting 12 dogs within a period of six months.

Leptospirosis is a zoonotic disease caused by Leptospira bacteria. Zoonoses, which are caused by bacteria, viruses or parasites, pass from animal hosts to humans and can occur via an intermediary host, similar to how the bubonic plague passed between humans and rats through fleas. This cross-species transmission can also transpire as a result of direct contact with infected animals or with free-living microorganisms.

The method of transmission was believed to have played a significant role in the epidemic that afflicted Native American populations in southern Massachusetts from 1616 to 1619. As their lifestyle put them in constant contact with rats, and thus their urine, they were continuously susceptible to contaminated soil and water, allowing the bacteria to thrive. In addition to exposure via bare feet, this would have allowed the bacteria to spread via sweat lodges, as it was common practice for families to bathe in cool ponds following a cleansing session.

Adolf Weil first described the traits of leptospirosis in 1886, earning it the name ‘Weil’s disease.’ Prior to then – harkening to its characteristic yellowing of the skin and eyes – it bore the moniker ‘infectious jaundice’ and was believed to have afflicted troops during the American Civil War and World War I, due to poor combat sanitary conditions.

While the disease is easily prevented by proper hygiene and treated with modern antibiotics, the United Kingdom’s National Health Service currently estimates that 7 million to 10 million people worldwide are infected each year, primarily in tropical and rural areas. However, because the Centers for Disease Control does not collect data on animal cases, the total number of infected animals worldwide is not known.

The most significant problem in eradicating a zoonosis is that it never truly goes away – unlike exclusively human diseases, such as polio, a zoonotic microorganism can maintain a presence in the populations of their ‘reservoir’ animal hosts for indefinite periods of time, before re-emerging and spilling over into human populations.

Carsten Brandt, D.V.M., an assistant professor of emergency medicine and critical care at the University of Florida’s College of Veterinary Medicine, noted the local presence of leptospirosis is not a recent development.

“Leptospirosis has always been in Florida,” Brandt said. “We just haven’t seen any for years.”

The bacterium, which is transmitted through the urine of infected animals, primarily small rodents, can survive in warm, moist environments, such as soil, for months on end.

In dogs, infections can take between two to 20 days before symptoms are exhibited. The initial symptoms – such as fever, lethargy and weakness – are generally non-descript.

“[It] always depends on how quickly we get them, how quickly the owner picks up on the disease process and when you start the antibiotic therapy,” Bandt said.

Once the bacterium reaches the kidneys, it can lead to organ failure. When this occurs – as it did in eight of the 12 recent canine cases – hemodialysis is needed.

“The indications for hemodialysis are what we call ‘overloaded,’ where they cannot produce urine,” said Leo Londono, an emergency room and critical care veterinary resident.

In hemodialysis, an external machine acts as a kidney when the patient’s – in this case, a dog’s – organs have begun to falter.

“We put a large catheter on their jugular vein and they sit on the table for five to six hours while we basically pull the blood out – not all at the same time,” Londono said.  “We cycle it through an artificial kidney, basically trying to get rid of the toxins that the kidneys are trying to get rid of.”

Depending on the severity of damage to the kidneys, the dogs may need anywhere from two to four sessions of hemodialysis to restore kidney function, in addition to antibiotic treatment and support with IV fluids. In especially severe cases – including the one dog that died – pulmonary hemorrhage can occur, filling the lungs with blood.

“You can manage the kidney part, manage the liver part, the fluid and all that,” Londono said. “But once they start bleeding into their lungs, there’s not much you can do.”

Unfortunately, once the infection has progressed to a pulmonary hemorrhage, it is very difficult to treat and often turns fatal.

“It’s just a bad disease all-in-all,” Londono said. “If you catch it in time, you have a good chance of treating it.”