Download Andrew Kim 7790-7232 The Effects of FV3 Ranavirus on the

Andrew Kim 7790-7232
The Effects of FV3 Ranavirus on the American Bullfrog and Aquatic Communities
In aquatic habitats such as pond ecosystems and lake communities around the eastern half of
North America, there is a problem that has made its presence known in American Bullfrog (Rana
catesbeiana) populations. Ranaviruses are this problem, and they have been gaining attention as an
emerging threat to bullfrog populations in the U.S. and to amphibians in general around the world.
Ranaviruses exhibit a parasitic relationship with bullfrogs in North America in that they increase their
own fitness by infecting and lowering the fitness of bullfrogs. Furthermore, ranaviruses directly,
negatively affect bullfrogs, but they also present a threat to the communities that bullfrogs live in. It has
been found that through different intra- and interspecific reservoirs, the ranavirus is able to infect not
only American bullfrogs, but also other members of the communities. Bullfrogs are frequently traded
globally, and human export and import of infected bullfrogs have helped spread the amphibian
ranavirus globally. It is necessary for traded bullfrogs to be screened. This could be enforced by
government agencies such as the U.S. FTC (United States Federal Trade Commission) that regulate trade
and would greatly help decrease the spread of ranaviruses globally.
The most noted strain of ranavirus that affects bullfrogs is Frog virus 3, FV3 for short. The virus
exhibits a parasitic relationship with bullfrogs because it infects the bullfrog and lowers the frog’s fitness
while increasing its own. The virus lowers a bullfrog’s fitness by decreasing mobility through the swelling
of limbs, anorexia due to forced fasting, and by killing the frog in many cases. FV3 has been labeled an
emerging threat and much research has been undergone recently to understand the effects that the
virus can have on aquatic communities around the world.
The virus is an effective parasite due to its virulence and survivability. Jason Hoverman and his
team conducted research as to the prevalence of ranaviral infection in pond communities and found
that infection was found in 83% of his 33 sample ponds. (Hoverman et al. 2011) FV3 is capable of
surviving outside of a host in an aquatic environment for extended periods of time and remains virulent
during this time. (Blaustein et al. 2012) A bullfrog that is swimming in water contaminated by an
infected host can be infected by FV3 in a matter of hours. (Miller et al. 2011) Combined with the fact
that FV3 ranavirus has been found to persist in multiple seasons makes for very problematic
transmission efficiency. In Hoverman’s research, his team found that ranavirus infections were found
over multiple seasons in a majority, 63%, of the ponds they sampled. (Hoverman et al. 2011) This means
that even in winter or other extreme seasons, the virus is able to persist and remain infectious. FV3 has
also been found to infect horizontally, which means that it doesn’t spread from parent to child but from
an infected host to any non-infected host without immunity. (Miller et al. 2011) This is can be seen
through the cannibalistic behavior of bullfrogs. Adult American bullfrogs will eat mostly anything that
will fit in their mouths, including smaller frogs and bullfrog larvae. If they consume any of the flesh of an
infected frog, they can contract the virus. (Miller et al. 2011) Although these characteristics make FV3 a
very efficient parasite, they are not the main factors that make FV3 the large problem for American
bullfrogs.
The factor that makes FV3 problematic for bullfrogs is its lethality and the symptoms it
produces in infected individuals. FV3’s deadly symptoms include organ failure in mainly the kidney and
liver, hemorrhaging throughout the body, and cell necrosis. (Blaustein et al. 2012, Miller et al. 2011)
These symptoms can result in the death of the host within a couple of days to a few weeks. (Miller et al.
2011) For most parasites, this lethality would present a problem because the parasite needs a host to
live. This would lead one to think that FV3’s lethality may seem like a negative for FV3 in that the host
dies, but the virus is able to persist in a host’s corpse for extended amounts of time. During this time, if
another bullfrog consumes any of the infected tissue of an infected corpse, the virus can easily be
contracted. (Miller et al. 2011) This is yet another factor that makes FV3 such a dynamic parasite. Other
than the lethal symptoms, FV3 may also produce severely crippling symptoms as well. These symptoms
may not immediately kill the host, but maim them to the point that their fitness is greatly reduced.
Symptoms such as these include bloated limbs which reduce mobility and anorexia. (Miller et al. 2011)
These symptoms greatly decrease bullfrog fitness because a bullfrog that cannot swim properly is easy
prey and a bullfrog that won’t eat will eventually die. Also, the probability that a male bullfrog with
impaired mobility will mate successfully is low due to the fact that it cannot compete with other males
to garner the attraction of a mate. All of these factors of transmission efficiency, lethality, and
survivability present a threat to the global communities that bullfrogs live in.
FV3 requires human attention because of its potential to harm not just bullfrogs and
amphibians, but the entire communities that they inhabit. It has been found that the horizontal
transmission of FV3 has been able to infect not only bullfrogs, but amphibians of other species and other
aquatic species as well. (Blaustein et al. 2012) When bullfrogs that were infected die, their bodies still
retain the virus. If the frog died inside of a pond or lake, the water then becomes infected as well
because the virus can sustain itself in an aquatic environment. This has been found to be responsible for
the infection of not only amphibians, but also some fish. (Mazzoni et al. 2009, Miller et al. 2007) The
disease has the same pathological effect on fish as it does on bullfrogs, and is a threat to the diversity of
species in aquatic environments that bullfrogs inhabit.
This threat is perpetuated by the fact that American Bullfrogs are a heavily traded commodity.
In Brazil, FV3 was found in a bullfrog farm and was responsible for a mass mortality event that
devastated the farm. (Mazzoni et al. 2009) This was due to the lack of screening prior to the shipping of
the bullfrogs from the U.S. to Brazil. The trade of infected bullfrogs is a very effective means of
transportation for FV3 as it becomes a global threat with the ability to pass beyond the borders of other
countries without hindrance. Noting the die-offs and the threat that FV3 poses to aquatic environments
across the globe, I propose that government organizations such as the U.S. FTC require screenings of
bullfrog exports and imports exports to lower the occurrence of FV3 globally.
FV3 is a very effective and dangerous threat. Its high transmission efficiency and ability to move
across the globe make it a necessary problem to deal with. American bullfrogs may be the main target of
FV3 in the U.S., but it has the potential to destroy entire communities and must be dealt with.
References
Blaustein, A.R., Gervasi, S.S., Johnson, P.T.J., Hoverman, J.T., Belden, L.K., Bradley, P.W., Xie, G.Y. 2012.
Ecophysiology meets conservation: understanding the role of disease in amphibian population
declines. Philosophical Transactions of the Royal Society Biological Sciences 367: 1688-1707.
Miller, D.L., Gray, M.J., Storfer, A. 2011. Ecopathology of ranaviruses infecting amphibians. MDPI Viruses
3: 2351-2373.
Mazzoni, R., Mesquita, A.J., Fleury, L.F.F., de Brito, W.M.E.D., Nunes, I.A., Robert, J., Morales, H., Coelho,
A.S.G., Barthasson, D.L., Galli, L., Catroxo, M.H.B. 2009. Mass mortality associated with a frog
virus 3-like Ranavirus infection in farmed tadpoles Rana catesbeiana from Brazil. Dis Aquat
Organ. 86: 181-191.
Miller, D.L., Rajeev, S., Gray, M.J., Baldwin, C.A. 2007. Frog virus 3 infection, cultured american bullfrogs.
Emerging Infectious Diseases 13: 342-343.
Hoverman, J.T., Gray, M.J., Miller, D.L., Haislip, N.A. 2011. Widespread occurrence of ranavirus in pondbreeding amphibian populations. Ecohealth 9: 36-48.