Biology Reference
In-Depth Information
a practical role in causing disease for humans. In Guam, it has been determined that
Bufo marinus
,
Anolis carolinensis
, and
Carlia ailanpalai
have high infection rates
for
Salmonella
species, including
S. waycross
, a serotype that contributes signifi-
cantly to high human salmonellosis rates in Guam but is rare in other countries
(Haddock et al., 1990). High prevalence of
Salmonella
in fenced yards that exclude
feral mammals has led to the inference that these lizards and toad are significant
contributors to the high prevalence of salmonellosis in Guam (Haddock et al.,
1993). In the United States, 6% of all
Salmonella
infections (and 11% of those in
patients <21 years of age) are related to contact with amphibians or reptiles, which
equates to approximately 74,000 cases/year (Mermin et al., 2004). Exposure in
these cases is attributable to keeping reptiles and amphibians as pets and not to
established populations of alien species per se. However, this finding does show
the potential for similar transmission via close contact with alien species - such
as house geckos and Cuban treefrogs - that are commensal with humans in the
tropics and commonly reside and defecate in homes or cisterns. As far as I know,
disease transmission via these routes has not been examined; however, health
officials in the British Virgin Islands attempt some control of Cuban treefrogs
because of their propensity to occupy cisterns used for collecting residential
water (Owen et al., 2006).
Cane toads serve as a mechanical vector for human helminths in its native range
(Marinkelle and Willems, 1964) and in Puerto Rico (Hoffman and Janer, 1941)
because of its coprophagous habits. Hence, they have been conjectured to serve as
vectors for human diseases or helminth parasites in areas lacking proper sanitation
(Hoffman and Janer, 1941; Freeland, 1985; van Dam et al., 2002). However, the
epidemiological importance of these conjectures in any portion of its introduced
range remains unexamined.
There is one documented case of human death following ingestion of three
cane toads that were mistaken for an edible species (Rabor, 1952). This species
has also been reported to cause illness in humans after handling (Allen and
Neill, 1956; Gebhardt, 1967) and after toxin entered open scratches (Gebhardt,
1967; Otani et al., 1969). Contamination of water sources by dead
Bufo marinus
has been reported for Palau (Gressitt, 1952) and Australia (van Dam et al.,
2002). In at least the former instance, contamination threatened scarce water
resources on an atoll. The threat is created by the sometimes large numbers of
toads that may die and rot in a water source, as well as their released toxins,
which may possibly be stable in such an environment for several days (van Dam
et al., 2002).
Tadpoles of
Bufo marinus
have been shown to have a depressive effect upon growth
rates in four species of mosquito and on survival rate in one species when reared
together in small containers of water (Hagman and Shine, 2007). Although many varia-
bles remain unresolved (e.g., cane toad effects on native anurans and native mosquito
predators, fitness of different size classes of mosquitoes), this has led to the speculation
that cane toads might potentially have a suppressive effect on mosquito populations in
the wild and lead to reduced transmission rates of mosquito-vectored diseases for
humans (Hagman and Shine, 2007).
