Disease Review: Leptospirosis

People have been interacting with animals ever since we can remember. We, humans, benefit from the animals around us. Animals provide food, livelihood, help us in our travel and companionship. They can even provide help in treating PTSD. There are a lot of things that animals do for us. We might come into contact with animals in many instances like in our households, during travel, enjoying outdoor activities, or visiting animal exhibits or zoos.

However, animals can be carriers of harmful disease-causing agents. Illnesses that are transmitted from animals to humans are called zoonotic diseases or zoonoses. Animals can appear healthy even when they are carriers of these harmful germs. 

A good example of a worldwide zoonotic disease is leptospirosis. Leptospirosis is a bacterial disease that affects humans and animals. It is an emerging zoonosis endemic in impoverished regions of the tropics that is sometimes transmitted in developed countries. 

Its Recognition and Discovery

Leptospirosis is thought to be in existence for millennia since man came in contact with wild animals, in particular rodents. There are no ancient texts or documents that can give clues on the origin of the disease. And since the disease does not produce changes in the bones, it is not possible to look for evidence in the skeletal remains of our ancestors. 

It is difficult to know when leptospirosis was first recognized as a distinct disease because many conditions produce similar symptoms. 

Scientists believed that when the black rats, Rattus rattus, reached Britain and Europe in the 12th century AD, they probably brought the disease leptospirosis from its origin region, Asia. It was transferred to the region with temperate climates by brown rats, Rattus norvegicus. 

The disease was first recognized in sewer workers by Landouzy in 1883. However, the first written history of leptospirosis began in 1886 when a professor of medicine at Heidelberg University, Adolf Weil, described four cases of an acute febrile illness accompanied by renal malfunction, jaundice and abnormal signs in the central nervous system. The term Weil’s disease was coined in 1887. 

In 1915, a group of Japanese scientists led by Inada and Ito discovered the causative agent of Weil’s disease. They called the bacteria Spirochaeta icterohaemorrhagiae.

Besides discovering the bacteria responsible, they were able to isolate the bacteria and determine the source and route of its infection. They discovered that rats are the primary carriers and reservoir of the bacteria. 

The Japanese group also experimented on the first leptospirosis immunization. They demonstrated that by injecting antibodies from humans or goats to guinea pigs, passive immunity could be provided to guinea pigs.

At that time, there were tendencies to confuse leptospirosis with yellow fever. Captain Adrian Stokes who had studied leptospirosis among Allied troops during World War I showed that leptospirosis and yellow fever were distinct diseases. Unfortunately, he died of yellow fever in 1927.

In 1989s, leptospirosis was recognized as a veterinary disease of major economic importance. Leptospirosis was found infecting different mammalian species. 

The Bacteria Responsible

Leptospires, bacteria that cause leptospirosis, are slender motile microorganisms. Their body, about five to seven microns, is in the form of a tightly wound spiral. 

They can survive in moist environmental conditions provided that the pH is near neutral. They can easily be killed by saltwater and acidic surroundings. They are found in many places. They are mostly found in the urine of most rodents, cattle, pigs, horses, and even domestic dogs. 

When the animal is infected, it may have no symptoms of the disease. Infected animals may continue to excrete the bacteria into the environment continuously. 

Humans can become infected through contact with the urine of the infected animal or contact with water, soil, or food contaminated with the urine of infected animals.

The bacteria usually enter the body through the abrasions or cuts in the skin. It can also enter through the mucous membranes (eyes, nose, and mouth). Inhalation of contaminated water or aerosols may also result in infection via the respiratory tract. Water-borne transmission of the disease has also been observed. 

The Disease and How to Fight it

Many of leptospirosis symptoms can be mistaken for other diseases. In addition, some infected persons may have no symptoms at all. 

The incubation period is usually 7 to 12 days but can be as little as two or as long as 26 days. The clinical illness of leptospirosis has two distinct phases, the septic, and the immune phase. Two clinical syndromes are observed in leptospirosis patients, the anicteric and the more severe, icteric leptospirosis. 

In anicteric leptospirosis, the septic phase is characterized by fever, abdominal pain, headache, vomiting, anorexia, and myalgia. The most common symptom is the reddening of the eye surface. The immune phase is characterized by less prominent fever, more intense headache, pulmonary involvement, aseptic meningitis, and rash. 

In icteric leptospirosis, the septic and immune phase are not as distinct. The septic phase resembles the anicteric leptospirosis. The immune phase is characterized by jaundice, vascular dysfunction, and azotemia.  

Death has been attributed to irreversible septic shock, acute respiratory failure, and multiple organ failure. Eye problems can occur in 10% of those who recovered from leptospirosis. 

Most patients with leptospirosis will be admitted to the hospital unless their illness is so mild that it is treated as a flu-like illness. 

Leptospirosis is usually treated with antibiotics including penicillin and doxycycline. For severe leptospirosis, intravenous antibiotics are given. Patients must be admitted to an ICU for supportive therapy and management of electrolytes. 

There is no vaccine available for humans but there are available preventive measures we can do to avoid getting infected. Education and information campaigns for the public on the modes of transmission of the disease will help. The risk of acquiring the disease can be greatly reduced by avoiding swimming or wading in potentially contaminated waters. 

Protective clothing and footwear should be worn by those who work in possible contaminated water and soil. Cuts and abrasions should be covered properly. 

All animals can potentially be infected with leptospirosis. While occurrence among pets was rare, the disease has been diagnosed more frequently in the past few years.