Four homeless people in Denver are struck with rare trench fever infection which plagued soldiers during World War I after being bitten by body lice

Colorado health officials are investigating an outbreak among Denver's homeless population of trench fever - a rare infection best known for afflicting soldiers in World War One. 

So far, health officials have detected four cases, with the last reported on Thursday. 

 The rare disease, which got got its name after it was known to infect WWI soldiers in the trenches of Europe's Western Front, is typically transmitted by body lice.

It is believed the infection is now affecting homeless people that have poor access to good hygiene.

People with compromised immune systems also are at higher risk of infection.

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Colorado health officials are investigating an outbreak of a rare infection known as Trench fever among Denver's homeless population (file image)

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The rare disease got got its name after it was known to infect World War I soldiers (pictured), and is typically transmitted by body lice among people who have poor access to good hygiene

After issuing an advisory on Thursday, health officials urged doctors to keep close eye for any new cases, Kaiser Health News reported. 

Previous outbreaks in recent years have occurred in homeless camps in San Francisco and Seattle.

Trench fever is caused by a bacterium known as Bartonella quintana, which is related to the same disease that causes cat scratch fever. 

It is transmitted in the feces of body lice. 

Symptoms include relapsing fever, bone pain - especially in the shins, headaches, nausea, vomiting and malaise.

Some of those infected can develop skin lesions or a life-threatening infection of their heart valves. 

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The feces of body lice is what transmits trench fever, which causes relapsing fever, bone pain (especially in the shins), headaches, nausea, vomiting and malaise

The disease enters the body through breaks in the skin, as well as through the eyes and nose. It is usually treated with antibiotics and by the removal of body lice. 

Health officials also warned that other cases of trench fever may also may have been overlooked, due to the attention being placed on the COVID-19 pandemic. 

Public health officials in the city are already battling the coronavirus, which has been confirmed in more than 40,000 cases in the state and blamed for more than 1,700 deaths.  

The economic hardships caused by the pandemic also may be exacerbating the spread of trench fever as more people are driven into homelessness. 

Dr. Michelle Barron, medical director of infection prevention and control at UCHealth University of Colorado Hospital, told Kaiser News that a trench fever diagnoses may be easy to miss.

Doctors often treating other ailments with similar symptoms will prescribe antibiotics and not notice that a patient may have had the infection. 

The bacteria responsible also can take up to 21 days to grow in a lab culture. She said that two of the confirmed cases in Denver had grown just before their cultures were about to be discarded.

Barron said she received a call last month from a lab after the third case was confirmed among homeless people in Denver. That prompted her into action.  

'Two is always an outbreak, and then when we found a third — OK, we clearly have something going on,' Barron said she remembered thinking at the time.

She had not seen a case of the disease for at least two decades and alerted public health authorities, who went forward with their advisory as a fourth homeless person was reported infected on Thursday. 

All the cases were reported months apart. 

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So far, health officials have detected four cases of trench fever among homeless people in Denver, with the last reported on Thursday. Tents pitched by homeless people are pictured in a park across from the State Capitol in Denver