Biomedical Engineering Reference
In-Depth Information
including antibiotic-resistant species [160]. Mosquitoes are reviled throughout the
world, and have been likened to flying, infected hypodermic needles. The mosquito
seems to serve no useful ecologic purpose (other than as a food source for bats, and
other insectivores). It has been speculated that if every genera of mosquito were elimi-
nated as a terrestrial species, there would be no significant negative ecologic repercus-
sions [161]. The mosquito-borne virus diseases are discussed in Chapter 38. A few of
the non-viral mosquito-transmitted diseases are listed here:
Malaria (Class Apicomplexa) is transmitted by species of Genus Anopheles.
Brugia malayii
is transmitted by
Aedes polynesiensis
and other species.
Wuchereria bancrofti
transmitted by
Armegeres subalbatus.
Dermatobia hominis
(human botfly) in which mosquitos carry the fly larvae, and the
larvae follow the mosquito entry point into the host organism.
Negative classifier A negative classifier is a feature whose absence is used to place an
organism into a taxonomic class; it is the riskiest way to assign classes. A species may
lack a particular feature because none of its ancestors ever had the feature, as might be
the case in a valid lineage of organisms. An example is the Collembola, popularly
known as springtails, a ubiquitous member of Class Hexapoda, and easily found under
just about any rock. These organisms look like fleas (same size, same shape) and were
formerly included among the true fleas (Class Siphonaptera). Like fleas, springtails are
wingless, and it was assumed that springtails, like fleas, lost their wings somewhere in
evolution's murky past. However, true fleas lost their wings when they became para-
sitic. Springtails never had wings, an important taxonomic distinction separating
springtails from fleas. Today, springtails (Collembola) are not classed with fleas or
with any member of Class Insecta. They belong to Class Entognatha, a separate sub-
class of Class Hexapoda. Alternately, taxonomists may be deceived by a feature whose
absence is falsely conceived to be a fundamental property of a class of organisms. For
example, Class Fungi was believed to have a characteristic absence of a flagellum.
Based on the absence of a flagellum, the fungi were excluded from Class
Opisthokonta and were put in Class Plantae, which they superficially resembled.
However, the chytrids, recently shown to be a primitive member of Class Fungi, have
a flagellum. This places fungi among the true descendants of Class Opisthokonta.
Non-phylogenetic signal DNA sequences that cannot yield any useful conclusions related
to the evolutionary position of an organism. Because DNA mutations arise stochasti-
cally over time (i.e. at random locations in the gene, and at random times), two organ-
isms having different ancestors may achieve the same sequence in a chosen stretch of
DNA. Long-branch attraction, mutational convergence, and adaptive convergence
account for many of the errors that occur when non-phylogenetic signal is incorrectly
assumed to have phylogenetic value [24].
Obligate intracellular organism An obligate intracellular organism can only reproduce
within a host cell. Obligate intracellular organisms can include any type of organism,
but the term aptly describes all viruses and all member of Class Chlamydia
(Chapter 13). Examples of genera that contain obligate intracellular species include:
Coxiella, Leishmania, Plasmodia, Rickettsia, Toxoplasma, Trypanosoma. See
Facultative intracellular organism.
Opportunistic infection, Opportunistic organism Opportunistic infections are diseases
that do not typically occur in healthy individuals, but which can occur in individuals
