Of mice (or rats) and man: The story of leptospirosis

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The Philippine Clinical Practice (CPG) Guidelines has classified leptospirosis as an endemic zoonosis in the Philippines. This means that it is occurring regularly and could be transmitted between animals and humans.

There is an average of 680 leptospirosis cases and 40 deaths from the disease reported every year.

It is seasonal with a peak incidence during the rainy months of July to October.

Lepto comes from the greek word that means “thin” and spira is latin for “coil”.

"Wounded rat in London. " by Jan van der Crabben, Wikimedia Commons is licensed under CC BY-SA 2.0
“Wounded rat in London. “ by Jan van der Crabben, Wikimedia Commons is licensed under CC BY-SA 2.0

It was aptly named because the spirochete bacteria looked like thin coils.

There are many Leptospira species but the most common cause of Leptospirosis come from the Leptospira interrogans strain.

Leptospirosis is a zoonotic infection, meaning it can be transmitted from animals, most especially rodents (rats, mice), to humans. Humans that are at risk are more often those that work in the sewers or farmers who wade in water that is contaminated with animal urine.

Transmission is usually via abrasions in the skin, which is why there is high risk of contamination when wading in flooded waters infected with animal urine for persons with wounds on their feet and legs.

The bacteria may also be transmitted through the eyes, especially when swimming in contaminated water, and rarely, it may come from contaminated food. The bacteria may also be transmitted via bite from an infected animal.

Currently, little is known of the pathogenesis of this bacteria but that it has virulence factors – these are molecules produced by pathogens that help it evade or attack the immune system so it can successfully colonize the host. Generally, the bacteria will usually occupy the bloodstream and spread throughout other organs.

Symptoms

There are two phases of Leptospirosis – the first one is called the Leptospiremic Phase in which the bacteria proliferate, cross tissue barriers and spread through the blood.

This is usually accompanied by symptoms like fever which may last for three to 10 days.

It is during this period that the Leptospira bacteria can be isolated from the blood stream, cultured and detected by PCR.

This is also where the various virulence factors of the Leptospira bacteria help it evade the immune system.

In this phase of the disease, Leptospirosis may present with non-specific – flu-like symptoms such as muscle pains, headache, fever and Conjunctivitis.

One may also experience photophobia and conjunctival suffusions. The eyes may gradually become red but without tearing or discharges.

While Leptospirosis can generally cause pain in the muscles of any part of the body, it’s usually characterized by calf pain and tenderness.

In theory, since leptospira are aerobic (oxygen loving) bacteria they are more attracted to the larger muscles of the calf which relatively contain more oxygen than the smaller ones around it.

The second phase is called the Immune phase – this is where the appearance of antibodies such as IgM coincide with the disappearance of the leptospira bacteria from the blood, it may be from recovering but in most cases the bacteria may have already invaded the organs.

Generally the signs and symptoms depend on the affected organ. With liver damage there may be jaundice, with kidney damage there may be kidney failure, reduced urine output and increased fluid retention leading to edema and swelling in the legs or in the face.

With lung damage, there may be difficulty of breathing and coughing up of blood. If the brain is affected, meningitis symptoms occur – which is commonly a headache with fever and stiff neck.

Unfortunately for some, the involvement of organs may be fatal. Leptospirosis has a death rate of 5-10% according to the journal, Future Microbiology. And according to the World Journal of Clinical and Infectious Diseases, this rate increases to 50-70% if Lungs are involved.

Weil’s Disease

Mild forms of Leptospirosis spontaneously resolve within 7-10 days and may only have flu-like symptoms. If a patient’s vital signs are stable, they can take oral medications, and they don’t have signs of organ damage such as difficulty of breathing or difficulty urinating they may be exempt from hospitalization. The rest of the cases need to be hospitalized for close monitoring.

When leptospirosis becomes severe, it’s known as Weil’s disease. And is most often seen with the triad of jaundice (a yellowing of the eyes and skin), kidney injury and hemorrhage / bleeding.

This is due to the bacteria having invaded and dealt sufficient damage to various organs such as the liver causing the jaundice, the Lungs in which it damages the alveolar capillary membrane and causes it to bleed resulting in hemorrhage and coughing up of blood and the kidneys leading to interstitial nephritis or tubular necrosis which subsequently causes kidney failure. Finally the bacteria may even occupy the brain causing Meningitis, this is why diagnostics may include collecting and culturing of Cerebrospinal fluid to determine infection.

Diagnosis, Treatment and Prevention

Leptospirosis is usually detected by culturing from the blood, CSF or urine which is the gold standard but it usually takes very long for the result to turn around. Serological tests, PCR, ELISA, and Rapid Antibody testing specific for leptospirosis may also be used.

Other laboratory parameters like clinical chemistry and urinalysis is usually requested to check for signs of end organ damage.

Leptospirosis is commonly treated with Penicillin G or Doxycycline. Supportive treatment is also done especially when multiple organs are affected like maintaining hydration through IV fluids, Oxygen and Respiratory support and Blood Transfusions.

Pre exposure prophylaxis is not routinely recommended and avoiding endemic areas is still the best way to prevent infection.

If this cannot be avoided protective equipment such as boots and goggles are recommended.

If a person is sure that he or she will be exposed to bacteria causing leptospirosis, doxycycline is the antibiotic used for pre- or post-exposure prophylaxis although it is contraindicated for pregnant women as it could affect the bones and teeth of the baby (yellow or gray discoloration) and alternatives such as Azithromycin is used instead.

Leptospirosis during pregnancy is highly associated with high fetal mortality rates.

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