Monday, January 5, 2009
Of birds and bats: histoplasmosis and human health
A recent report from the Centers for Disease Control should remind us of the importance of managing urban bird and bat populations. In the December 19 edition of the Morbidity and Mortality Weekly Report (MMWR), there is a report about a Pennsylvania-based, church mission group who had been renovating a church in Nueva San Salvador, El Salvador. It turns out that as part of the renovations involved cleaning and sweeping around some bird and bat roosting areas. Nine of the 11 persons with the initial group returned home with flu-like symptoms. The symptoms were eventually diagnosed as histoplasmosis, a disease caused by inhaling the spores of a fungus, Histoplasma capsulatum. Eventually eleven more volunteers from two other missions groups from Pennsylvania and Virginia, working at the same church at approximately the same time (Feb-Mar, 2008), also met the case definition for the disease.
Histoplasmosis is a pest-borne diseases that PMPs often hear about, but rarely encounter (at least knowingly). It is not a disease that requires travel to the tropics. The pathogen is common in the U.S., and the disease is probably more common than most of us realize.
The fungus live in soil, and people typically get infected when they breath dust from soil in areas where H. capsulatum naturally occurs (the term for this is "endemic"). According to NIOSH publication 2005-1009, H. capsulatum is endemic throughout the U.S., although the proportion of people infected by H. capsulatum is higher in central and eastern states, especially along the Ohio and Mississippi River valleys. Fortunately, once contracted the disease is not contagious.
The interesting thing about this disease, from the perspective of the PMP, is that "the fungus seems to grow best in soils having a high nitrogen content, especially those enriched with bird manure or bat droppings." The organism is believed to be carried on the wings, feet, and beaks of birds thereby increasing the risk of infected soil under bird or bat roosting sites or in manure accumulations inside or outside buildings. Some bird species whose roosts have been shown to be contaminated include blackbird (starlings, grackles, red-winged blackbirds, and cowbirds) pigeons, chickens and bats. Some are concerned that growing problems with Canada geese could also be contributing to spread of the disease to people.
Because the fungus cannot infect birds, there appears to be little risk of contracting this disease from bird droppings on window ledges or inside buildings. It's only when these droppings contact infested soil, that the fungus is able to spread and become a health risk.
Bats are a different story because, according to the CDC, they can become infected with the pathogen. So bat droppings can be potential sources for infection.
How bad is it?
Histoplasmosis symptoms vary greatly. Most people who contract the disease show no, or only mild symptoms. In some of us, histoplasmosis will result in flu-like, respiratory symptoms, including including a general feeling of illness (malaise), fever, chest pain, dry or nonproductive cough, headache, loss of appetite, shortness of breath, joint and muscle pains, chills, and hoarseness. In some cases, the disease can become chronic and result in more serious complications, even death.
Histoplasmosis may not be one of the most serious diseases we will be exposed to during our lifetimes, but because it is rarely diagnosed, it probably causes more lost work days that we realize. And it is certainly able to make us sick enough to miss work.
What should PMPs do?
The first concern of a pest management professional who encounters bird or bat infestations is to take steps to reduce the risk of breathing H. capsulatum spores. When working in dusty areas with bird or bat droppings, a good respirator should be worn. All it takes to cause infection and subsequent development of histoplasmosis is a brief exposure to inhaled contaminated dust. Remember that not all air filtering devices are equal and "people have developed histoplasmosis after disturbing material contaminated with H. capsulatum despite wearing either a respirator or a mask that they assumed would protect them." For detailed information about different respirator types and when they might be needed, see the NIOSH guide section on respirator protection.
In addition to breathing protection, disposable overalls are recommended by the CDC. This reduces the risk of worker and family exposure to dust that settles on clothing during exposure to contaminated soil.
Knowing how to protect your customers is also critical here. In areas where public access is minimal, or where remediation of droppings is taking place, the posting of signs warning people about histoplasmosis risk is a prudent first step. Anywhere that bird droppings sit on soil should be considered a high risk site for histoplasmosis. The public and unprotected workers should also be restricted from any areas with bat guano accumulations.
Areas that are being cleaned up should be sprayed with water to minimize dust movement. Obviously bird and bat control, and modification of the roosting environment are critical elements in reducing the long-term risks associated with this disease and others.
Histoplasmosis is only one disease risk caused by bird and bat roosts around human activity areas. While we shouldn't fear or loath birds and bats in natural settings, management of their roosting areas in urban locations are an important part of what our industry does.