|
By Katherine
Harmon | December
11, 2011,
www.scientificamerican.com
The tropics
are a warm, wet and wonderful place for plant, animal and other life to
flourish, and in all of that diversity are some bizarre and fascinating
fungal parasites that
make their living on—or at least find a temporary home in—us.
A session called “Adventures
in Tropical Dermatology”
last week at the
American
Society of Tropical Medicine and Hygiene’s annual meeting(ASTMH)
in Philadelphia featured a collection of slides depicting conditions that
would be enough to anchor anyone to the temperate zone, come hell or high
water. But the organisms that resulted in the frequently grotesque images
were impressive examples of incredible adaptation or revealing of surprising
gaps in human defenses.
The following are
some of the highlights—which, for the brave, are just a Google search away.
Four infective
fungi
One of the more entrancing slides showed a man’s shoulder covered in
rounded, off-white concentric ovals, tracing a path that spread over the
chest and back, almost like coral. The fungal infection, known as tinea
imbricata, is caused by the fungus Trichophyton concentricum, which lives
primarily in Southeast Asia, Central and South America and the South
Pacific.
A second fungus that has made its way up from the tropics as far
north as North Carolina is Lacazia loboi, which causes the skin
infection lobomycosis. The more northerly carriers of the fungal infections
so far have been bottlenose dolphins; in humans, the infection is still
primarily limited to Central and South America. The fungal spores can enter
the body through a skin abrasion, such as a scratch or bug bite. The human
immune system, however, does not seem to mount
a defense against the invader,
leaving it relatively free to spread in the body and create a fungal network
of bumps under the skin.
Another tropical fungal escapee is chromoblastomycosis, which is
often caused by one of four types of fungi that are commonly found breaking
down plant matter in forests. This infection is often kicked off by a
splinter and once inside the body, “we really elicit no defense or
immunological response,” Scott Norton, of Georgetown University Hospital,
said at the ASTMH meeting. Although cases are mainly confined to warm
climates, there have been some cases reported in northern Asia and Europe,
including some from old Finnish saunas.
Splinters or
other puncturing objects can also be the vector for eumycetoma, another
fungal disease against which the human body does not mount much of an immune
response, Norton noted. The implanted, unchecked fungus, which might be one
of many species, “can grow so luxuriantly that it can become a whole
colony,” he said. Eventually, the infected area—often the foot or hand of
agricultural workers—will swell and begin to extrude grains of different
colors depending on the species of
infecting fungus. |