There are many other infections with similar symptoms, from influenza to obscure tropical diseases, and usually the only way to tell is to take a blood or urine sample and run an assay. Leptospirosis is a very variable illness and even to experts it can be mistaken for other conditions, so if in doubt – test!
Where people have been exposed to the bacteria through contaminated water, there is a possibility of other infections at the same time, and these can cause symptoms that make the leptospirosis difficult to notice, especially if it doesn’t produce some of the classical warning signs like a skin rash. ‘Flu-like illness’ is easy to miss if you’re suffering from gastroenteritis at the same time, and this is one of the reasons why so many cases of leptospiroisis are not reported to anyone.
Because of the vague nature of the illness in the first few days it can be identical to many other infections, the most common of which we have listed below along with any differences (often there are none). The only realistic option for patients is to consult their doctor and have a blood test, as waiting for the illness to develop more recognisable symptoms may be a problem for some of the items on this page.
Influenza
Also shows a fever, headache, nausea and muscle pain but there is no skin rash, and inflammation of the eyes is uncommon. The fever from influenza usually passes in one or two days whereas the fever from leptospirosis, in moderate to severe cases, lasts three to five days. Mild cases are impossible to tell apart so blood testing is required to diagnose.
Meningitis
Leptospirosis produces many if not all the symptoms of meningitis, so blood testing is required to diagnose.
Hepatitis
Patients with severe leptospirosis often show jaundice, and can be confused with viral hepatitis – however the other symptoms of leptospirosis (hemorrhages, severe muscle pain, headaches, etc.) can be used to differentiate. Also the fever for viral hepatitis passes very quickly.
Yellow fever
This occurs only in certain countries, and has an incubation period of 3 to 6 days. It follows the same two-phase course as leptospirosis and both stages have identical symptoms so the only diagnostic tools are blood tests. There is a human vaccine for yellow fever, which is spread by mosquito bites.
Hemorrhagic fever
There are a group of hemorrhagic fevers (Lassa, CCHF, Ebola, Marburg, etc.) and all develop similar sudden-onset symptoms of pain, nausea, bleeding and skin rashes, so blood testing is required to diagnose. Patients with suspected hemorrhagic fever will be isolated as some of the viruses involved are extremely contagious. Diarrhoea is often seen, which is not common in leptospirosis cases.
Dengue fever
A viral infection also spread by mosquitos and with severe flu-like sypmtoms but rarely fatal. Symptoms in the first few days are identical to leptospirosis and blood testing is required to diagnose.
Malaria
A parasitic infection spread by mosquito bites, with fever, headaches, vomiting and chills developing after 10 to 15 days. Onset is slightly slower than leptospirosis and pinprick rashes are rare.
Lyme disease
Another bacterial infection (also a spirochete) that is spread by a tick bite and is common in the USA and Europe. A very characteristic circular rash is seen near the bite after 3 to 30 days, gradually expanding to cover up to 30cm in a few days. Other symptoms are generalised and can be mistaken for leptospirosis if the rash is not noticed. As with leptospirosis there is a high incidence of long-term ill health following infection.
Type I decompression sickness
Caused by nitrogen bubbles in the blood following rapid ascent from deep underwater dives, the main symptoms are pain and a skin rash, often the pain is joint-related and can be reduced by applying pressure to the skin over the affected area. Onset is rapid (a few minutes) but can sometimes be triggered by diving and then performing a later activity that reduces air pressure (such as commercial flying). There is usually no fever but in severe cases a wide variety of symptoms can develop.
Rift valley fever
A viral infection known to occur in Africa, with identical early symptoms and an incubation period of 2 to 6 days. Spread by contact with the body fluids of infected animals (many species can carry the virus including livestock) or the consumption of uncooked meat or milk. Blood tests are required to diagnose.
Legionellosis
Also called Legionnaire’s disease, this can present with similar symptoms of fever, headache, nausea, muscle pain, mild cough and later signs of hemorrhage and pneumonia. The onset of legionellosis can be from a few hours to 10 days, but there is rarely a skin rash in the first few days. The cough develops more rapidly than in leptospirosis, and the headache more slowly.
Nipah and Hendra virus
Two infections only recently discovered, they usually cause mild flu-like illness with a 4 to 18 day incubation period, but in severe cases can appear very similar to leptospirosis. There is no known medical treatment or vaccine, but cases are extremely rare and seem to be closely associated with handling infected animals during slaughter. Spread by fruit bats in the Australasian and Indonesian areas.
Plague
An infection from the Yersina pestis bacterium, spread by the bites of fleas and with a 3 to 7 day incubation period. Sudden early symptoms are very similar to leptospirosis. In the common bubonic form the lymph nodes swell rapidly and form painful swellings that can often break open. Rarer septicaemic and pneumonic forms are more difficult to tell apart without blood tests.