Patrick Guilfoile: Pregnancy tests, fungus and dead frogs
Pregnancy tests have changed substantially over the years.
The current tests use an antibody to detect a hormone in the urine found only in pregnant women. This test is simple, quick and quite accurate.
But earlier pregnancy tests weren’t quite as simple. One of the original tests, developed back in the 1920s, involved injecting urine from a potentially pregnant woman into a rabbit.
A few days later, a technician killed the rabbit, and its ovaries were examined for the presence of changes associated the same pregnancy-related hormone detected with modern tests.
By the 1940s, this test was refined to use African clawed frogs, which lay eggs after an injection of urine from a pregnant woman due to the presence of that same pregnancy-associated hormone.
Consequently, these frogs were widely imported to the United States for pregnancy tests (and other purposes). In some cases, the frogs were released into the wild and became established in parts of the U.S.
On a parallel track, it became clear that a fungus infection was at least a contributing factor in the dramatic reduction in frog (and other amphibian populations) worldwide.
Research had also demonstrated that this particular fungus was common in these African frogs, and yet they didn’t seem to be seriously affected.
Scientists identified the first known case of fungal infection in native frogs in the U.S. in the 1960s, at the same time that African frogs were widely used in the U.S. for pregnancy tests and other purposes.
Recently, researchers from the several institutions in California linked together the connection between feral African clawed frogs and the fungus infections in native American frogs.
These African clawed frogs had been released into the wild and became established in several places in California.
The scientists found that about 13 percent of wild-caught African clawed frogs in California had the fungus, and consequently, had the potential to transmit the fungus to native frogs.
When new pregnancy tests became widespread in the 1970s, and the frogs were therefore no longer medically useful, some of the African clawed frogs, which carried the deadly fungus, were apparently released into the wild.
These released frogs may have then transmitted the fungal disease to native frogs and other amphibians. Consequently, importing African clawed frogs to the U.S. for pregnancy tests may have contributed to the decline of amphibian populations in the U.S. and elsewhere.
PATRICK GUILFOILE has a Ph.D. in bacteriology and is the associate vice president at Bemidji State University.