Debra Jones
Biology Lab 1615
Title: Rabies prevalence in migratory tree-bats in Alberta, the influence of roosting ecology,
and sampling method on reported prevalence of rabies in bats.
Introduction: Rabies is an acute viral infection caused by inflammation of the brain and
spinal cord that affects mammals all over the world, excluding Antarctica. Reports from as early
as the 1800’s, states that rabies in wild dogs was highly prevalent. In 1921, a rabies virus was
discovered in fruit bats in Brazil, and later in Trinidad from several different species of bats.
North America’s reported of an insectivorous bats in 1953. Education of the rabies virus brought
about safe and effective vaccines to help control the amounts of rabies cases in North America,
in connection to domestic animals and wild life. The one exception to this is bats. Bats have a
natural tendency to carry the rabies virus. Since vaccines have been developed to destroy the
rabies virus many forms of rabies have not been able to flourish. Cases of dog rabies, for
example, have been eliminated. The previous conclusion that the main source of rabies in
humans came directly from dogs was incorrect. Rather the source has been found to be from
bats, not dogs. Because bats are nocturnal, they are difficult to study in their natural population.
Bats are elusive which makes it difficult to capture a sufficient amount of them to get accurate
results. Bats live high up in the leaves or down deep in the tree trunk, which makes it difficult to
get to them.
Reasons for research: The main reason for this study is to increase awareness of bats with
rabies, and ways we can protect ourselves from this virus. Researchers indicate that human
contact with infected bats fluctuates up and down, which causes changes in rates of rabies
infections.
Researchers have had the opportunity to study bats at several different wind energy
facilities. Since these facilities have been developed, large numbers of bats have died from
getting caught in the turbines. These deaths mostly involve migratory and tree-roosting bats. L
cinereus and L noctivagans make up 90% of the bats that are being tested for rabies. Although
people are concerned about the effect the wind turbines will have on the environment, it provides
an ideal situation to be able to study rabid bats, since it already involves euthanasia of the
animal. Researcher’s main objective for testing bat carcasses is to compare rabies prevalence
from the wind energy facilities to estimates in literature. Researchers then hypothesized that
urban animals have higher reported rabies than bats that frequently roost in close proximity to
humans.
Materials and Methods: Bat carcass samples were collected from three different wind energy
facilities in 2007 and 2008, and the bats sex, species, and date of death was determined.
Scientists at the Center for Disease Control in Atlanta, GA. then extracted RNA from the brain
tissue by using TRizol. The RNA was then used to grow cultures to make a saline to inoculate
the virus. Scientists then studied and compared the literature and government reports done over
the past 56 years, with their current findings for rabies prevention in North America. A “chisquare” was then used to compare rabies prevalence from its studies compared to literature
estimates. Scientists used the data they received, such as bat dwellings and roosting, to
determine the number of positive cases of rabies in bats.
Results: During the two year study, the bat carcasses received at the study sites, were suitable to
be used in the rabies testing. It was discovered that the nonsynanthropic bat species had higher
rabies presence (7.8% n=12,165) than the synanthropic species (4.2% n=52,931).
Discussion: As predicted, scientists’ estimates of rabies prevalence were lower than those
reported for L cinereus and L noctivagans from passive surveillance. The percent of rabiessuspect bats submitted to the CDC tested positive for rabies is around 9-10%, although both
species that were tested from their natural habitat tested lower for rabies prevalence. Bats have
adapted new roosting places such as buildings and bridges, but some species still prefer to roost
in trees, caves and crevices. If bats roost in places where there is a high amount of contact with
humans, the amount of rabid bats is higher. When bats roost in a more solitary place with less
contact with humans, the chance of being infected is much lower. When bats live together in
large colonies, the risk of infection is much greater because there is more opportunity to rub
against or be bitten. This is how the rabies virus spreads throughout a colony. These bats tend to
be somewhat paralyzed, and are unable to fly. Whereas, when bats live in solitary environments,
they tend to be more aggressive when infected with the rabies virus. These bats seek out other
individuals to infect, even attacking in mid-air. These are also the rabid bats that get caught in
the wind turbines.
Conclusion: In conclusion, the spread of the rabies virus mostly has to do with how bats roost,
because other contributing factors have not been investigated. Knowledge, tolerance, and
discretion are needed if humans and bats are to co-exist, and enjoy the ecosystem services that
bats provide for us.
Bibliography: http://www.jwildlifedis.org/content/47/1/64.full