Environmental Engineering Reference
In-Depth Information
Routine environmental sampling is not usually advised, except for water qual-
ity determinations in hemodialysis settings and other situations where sampling
is directed by epidemiologic principles, and results can be applied directly to
infection-control decisions.
In summary, environmental measures for prevention of infectious diseases
are a well-acknowledged component of public health. Since air and water are
common vehicles for transmission of viruses and bacteria, the scope for increased
participation of the environmental engineering community is vast.
Arthropodborne Diseases
Arthropod or insectborne diseases are an important class of diseases that affect
millions of people worldwide. They have a long history of causing human suffer-
ing. The bubonic plague that devastated Europe in the late medieval period was
transmitted via bites from a flea. Today, malaria is an archetype mosquitoborne
disease for research.
The addition of an arthropod species to the transmission cycle results in a more
dynamic and complex ecological to understand, but one which offers additional
avenues for intervention. Again, multilevel responses have been shown to be most
effective against vectorborne diseases, just as they have been for other infectious
agents.
A
host
is a person or other living animal, including birds and arthropods, that
provides subsistence or lodgment to an infectious agent under natural (as opposed
to experimental) conditions. Some protozoa and helminths pass successive stages
in alternate hosts of different species. Hosts in which the parasite attains maturity
or passes its sexual stage are
primary
or
definitive hosts
; those in which the
parasite is in a larval or asexual state are
secondary
or
intermediate hosts
.A
transport host
is a carrier in which the organism remains alive but does not
undergo development.
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The infectious agent can be a virus, bacteria, or multicellular organism. We
refer to the arthropod that delivers the infectious agent to humans as the
vector
.
Vectors can involve simple mechanical carriage of the infectious agent by a
crawling or flying insect through soiling of its feet or proboscis, or by passage
of organisms or eggs through its gastrointestinal tract. This does not require
multiplication or development of the infectious agent within the arthropod. The
other type of vector-agent interaction involves a more complex biological process;
the pathogen will undergo transitions in its life cycle while inside the insect. The
transition is required before the arthropod can transmit the infective form of the
agent to humans. The
extrinsic incubation period
is the time a pathogen requires
to develop or multiply in the vector before it can be transmitted to another
host. The infectious agent may be passed vertically to succeeding generations
of arthropod (transovarian transmission); transstadial transmission indicates its
passage from one stage of life cycle to another, as nymph to adult. Transmission
may be by injection of salivary gland fluid during biting or by regurgitation, or
deposition on the skin of feces or other material capable of penetrating through
the bite wound or through an area of trauma from scratching or rubbing.
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