EXPERT REACTION: Thai boys being freed from cave - Possible infections

Histoplasmosis (Cave disease) is a disease caused by the fungus  Histoplasma capsulatum  .

The Symptoms of this infection vary greatly, but the disease affects primarily the lungs .

Histoplasma capsulatum is found in soil, often associated with decaying bat guano or bird droppings.

In a cave environment the longer the time spend exposed to the environment the more likely that the spores from the fungus of soil Histoplasma capsulatum will be inhaled. Once inhaled the spores will settle into the lung.  Symptoms will begin 12–14 days. Most affected individuals  show no apparent ill effects.

Acute  histoplasmosis is characterized by non-specific respiratory symptoms, often cough or flu-like. Antifungal drugs are used to treat severe cases of acute histoplasmosis and all cases of chronic and disseminated disease.

However  Histoplasmosis is not contagious; it cannot be transmitted from an infected person or animal to someone else.

It is not a surprise that there is concern about the children developing pneumonic histoplasmosis (which is caused by a fungus named Histoplasma capsulatum). This disease has been known for a long time as "caver's disease". It occurs around the world, but very common in humid conditions, hence caves. Victims can get exposed by inhaling the fungus spores, which can exist in the soil or droplets of infected birds or bats. However, caves can also be a fertile ground for many already known infectious diseases such as rabies (exposure to infected bats), leptospirosis (exposure to infected rodents urine), tick-borne relapsing fever and many others. Caves make excellent environments for bats and bats make excellent reservoir for many viruses. That is why virologists are studying bats from caves for their potential carriage for lethal viruses, such as Ebola and Nipah viruses. 

Yet, it is also very important to consider that a very small portion of the caves on planet earth have been discovered and the microbial ecology of the discovered caves are heavily understudied! 

Thus, the risk of encountering other undiscovered pathogens is very likely. After our expedition for the recently discovered Imawari Yeuta cave in Venezuela we studied the cave microbial ecology and the results were astonishing! Less than one third of the samples we have collected had bacterial species that are known to science. However many of the samples had unclassified types of bacteria (unrevealed to science before) - but it is too soon for us to know if these are useful or harmful microbes. I really hope that the cave kids story in Thailand will stimulate the public and funding agents to support scientists to carry out more research to study innovative ways to tackle infectious diseases, particularly those occurring from exposure to the environment. 

Histoplasmosis is a very serious fungal disease caused by Histoplasma capsulatum, a fungus that lives in soil enriched with bat and bird guano, and it can reach high concentrations in bat caves. However, it’s not a communicable disease; it isn’t passed from person to person or animal to person. Infection occurs when a large amount of the fungus is inhaled from the environment. To the best of my knowledge, there is no recorded case of infection being transmitted by coughing or touching.
 
If contracted, there are various degrees of infection. Generally, in a healthy child or adult the immune system will deal with the disease and they will only show flu-like symptoms if any symptoms at all. The boys in Thailand should have healthy immune systems but may perhaps be compromised by malnourishment, and their quarantine may be to deal with any potential contamination of hair, clothing or other belongings.
 
If histoplasmosis does progress – which can sometimes happen even in otherwise healthy people and it’s not known why this happens in some cases and not in others - the initial flu-like symptoms can turn into a pneumonia-like condition. In a very small number of cases, there is dissemination to other organs and this is a very grave condition. There is a small number of drugs that can be used in treatment but at the latter stages these aren’t terribly effective and can have serious side-effects. Recent data suggests even with treatment, the mortality level in people with disseminated disease can be up to 50%

Caves can present a danger for a relatively rare fungal infection called Histoplasmosis (histo). It mainly infects the lungs but it can spread throughout the body. It is much more common in some areas of the world especially in parts of the USA (Ohio Valley), but also in parts of Canada and India many people seem to be exposed. Histoplasmosis is found around the world e.g. in Australia but here it is very rare.

Caves with large numbers of bats or birds and their droppings seem to be a higher risk for histo. Presumably the droppings allow the fungus to grow better in the dirt/soil and then people inhale the fungal spores.

How much the risk is in Thailand, I don’t know. I would need information from local health authorities on how often they see histo cases to better evaluate the risk for caves in Thailand.

Water is a risk for many infections. If there is a wound or skin cut, then water loving bacteria such as vibrio, Klebsiella, Enterobacter can be common bacteria that infect wounds. Bacteria such as legionella can be inhaled or ingested if in water and if water is contaminated by animals then it is bacterial diseases like leptospirosis or salmonella that could be a problem. 

Meliodiosis is also common bacterial infection in Thailand with water a common source for infection.

If water is contaminated with human waste, then that can be a risk for viral and bacterial infections for example typhoid, if people are carrying this bacteria.