Bonn: Researchers at the University of Bonn and the German Center
for Infection Research (DZIF) have discovered two new groups of viruses
within the Bunyavirus family in the tropical forest of Ivory Coast.
Previously only five groups responsible for serious illnesses in humans
and animals were known. Most are spread through blood-feeding insects.
Based on the discovered viruses researchers conclude that the ancester
to all bunyaviruses must have existed in arthropods such as insects. The
results are now being published in the “Proceedings of the National
Academy of Sciences” (PNAS).The bunyavirus family
includes five different groups of viruses which trigger serious
illnesses in humans and animals and which can also cause significant
damage to vegetables, such as tomatoes. The first viruses of this family
were discovered in a place known as Bunyamwera in Uganda, from which
they derive their name. "The most well-known bunyaviruses include, for
example, the Rift Valley fever virus, which can cause febrile illnesses
with severe bleeding in humans," says Dr. Sandra Junglen from the Bonn
Institute of Virology, also affiliated with the German Center for
Infection Research. In 2011, the "Schmallenberg virus" gained much
attention: also a part of the Bunyavirus family and transmitted by
gnats, it caused severe fetal malformations in ruminant animals
including sheep in the German Sauerland region.
Not in
Schmallenberg but instead in the African tropical forest of the Ivory
Coast, where the virologist has been conducting research for more than
ten years, she set off on the search for new viruses. Because most
bunyaviruses are transmitted by blood-sucking insects, Dr. Junglen
caught more than 7500 mosquitoes. Sorted according to species and sites
of capture, the scientists combined the captured mosquitoes into 432
mixed samples. In 26 of these samples, the researchers discovered
particles of unknown bunyaviruses.
Agents of human disease have developed from insect viruses
"These
were two groups of as-yet-unknown viruses which we called Jonchet virus
and Ferak virus," reports the virologist. The scientists obtained
fragments of the viral genetic material from the insect samples and
joined these fragments together like a puzzle, thus reconstructing the
entire genome sequence. "That alone took four years," reported lead
authors Marco Marklewitz and Florian Zirkel. During the comparison of
the genetic information with other viruses, it was found that Jonchet
and Ferak viruses are two phylogenetically independent bunyavirus
lineages.
How dangerous are the two new groups of viruses – can
they be easily transmitted to humans and animals? To answer these
questions, the scientists went in a new direction: They performed
infection trials in a large number of cell cultures at different
temperature levels. While pathogenic bunyaviruses can multiply at
temperatures that include the human body temperature, growth of Jonchet
and Ferak viruses ceases above 32 degrees Celsius, making it unlikely
that the viruses infect humans or other vertebrates. "In addition, we
reconstructed the evolutionary history of host associations of the
entire family of viruses, demonstrating for the first time that viruses
affecting vertebrates developed from arthropod-specific viruses," says
the researcher from the University of Bonn Hospital.
Simplified test to test novel viruses for risk of human infection
Triggered
by epidemics such as SARS and Ebola, virologists are now reaching out
to discover the plethora of unknown viruses lurking in natural
reservoirs such as insects, in an attempt to forecast pandemic risks.
„We hope our temperature test for estimating the risk of vertebrate
infection can be useful for assessing other viruses that keep being
discovered," says Dr. Junglen.