New Tests for Chlamydia
Chlamydia is a bacterium that can survive only by growing inside
other living cells.
There are over 60 strains that can infect most birds and mammals, including
humans. In humans, Chlamydia causes an eye infection leading to
blindness (trachoma), sexually transmitted diseases, and respiratory disease.
It has recently been associated with coronary atherosclerosis.
In animals, Chlamydia causes respiratory disease, conjunctivitis,
arthritis, enteritis, and reproductive failure. In birds, it produces a
generalized infection resulting in lethargy and sometimes death.
Until recently, the primary way to study this ubiquitous bacterium in the
laboratory has been to grow it in cell culture or in fertilized chicken eggs.
Now, Agricultural Research Service
(ARS) scientists at the National Animal Disease Center in Ames, Iowa-- the only
researchers in the United States who study a large variety of non-human
chlamydial strains--have tests that will enable scientists and laboratory
diagnosticians to detect any kind of Chlamydia and to identify its
Developed by veterinarian Arthur A. Andersen and molecular biologist Karin
D. E. Everett, the tests use polymerase chain reaction (PCR) to target genetic
material found in all chlamydial strains. The only DNA-based test now
available--one that identifies human chlamydial strains--doesn't detect animals
strains, which in some cases affect humans.
The new tests to diagnose Chlamydia take only about 4 hours, compared
to 2 to 4 days--or longer--needed to isolate the organism in tissue culture. An
added bonus: The tests don't require culturing specimens, thus reducing human
exposure to bacteria. ARS is pursuing a patent for the tests.
The diseases and host range associated with each strain are related to their
species classification. Currently, the strains fall into four species: C.
trachomatis, C. psittaci, C. pneumoniae, and C. pecorum.
Because the tests provide more detailed information about each species, the
scientists are reclassifying Chlamydiaceae into nine groups.
The new tests will help veterinarians diagnose and improve treatment for
sick birds and animals. Most important: They will help answer questions about
where people and animals become infected.
The researchers are currently studying Chlamydia in pigs. Even though
Chlamydia has been known to occur in pigs for over 40 years, it has been
very difficult to isolate. Andersen and ARS biological laboratory technician
Linda Hornung and University of Nebraska veterinarian Douglas Rogers in Lincoln
have isolated it from healthy and diseased pigs.
The new diagnostic test could also replace slower and less reliable tests
used by veterinarians to detect infected birds and prevent their sale as pets.
"One of our goals is to find out how widespread this bacterial organism
is among animals and what problems it's causing. We know that Chlamydia
is widespread in birds and animals and that it often is not properly
diagnosed," says Andersen.--By Linda Cooke McGraw, Agricultural
Research Service Information Staff.
Arthur A. Andersen and Karin
D. E. Everett are in the USDA-ARS Avian and Swine
Respiratory Diseases Research Unit, National Animal Disease Center, P.O.
Box 70, Ames, IA 50010; phone (515) 239-8338, fax (515) 239-8458.
"New Tests for Chlamydia Strains" was published in the June
1998 issue of Agricultural Research magazine. Click
here to see this issue's table of