Biomedical Engineering Reference
In-Depth Information
Salmonella, Shigella, herpes B, hepatitis A virus, and
tanapox virus are examples of agents documented to have
been transmitted to humans from naturally infected
nonhuman primates. Use of specific pathogen-free animals
can reduce the potential for infection from animals carrying
known agents. An adequate quarantine period that allows
a veterinarian time to observe the animal, perform diag-
nostic tests, and give appropriate treatments or vaccinations
can help prevent the introduction of disease into a stable
colony. There is no guarantee that quarantine periods of
30
e
90 days will be adequate to detect certain endemic
diseases such as tuberculosis. Diligent monitoring must be
maintained after animals are introduced to the general
colony. The susceptibility of workers is determined by their
immune status, which is dependent on their prior disease
history, vaccination status, and overall health.
Three additional conditions must be met for work-
associated infection to occur: the infectious agent must
leave the animal, be transmitted to a host, and enter that
host. Understanding these mechanisms provides the basis
for selecting appropriate biosafety measures.
example, can increase the concentration of airborne
microorganisms in an animal room by a factor of 10
e
100.
The smaller the particle, the longer it remains airborne, the
more likely it is to move with air currents, and the more
likely it is to be inhaled. Inhaled aerosolized particles in
the 5-
m
m range are most likely to be retained in deep
pulmonary spaces and therefore establish foci of infection.
Infectious aerosols are particles that may contain a single
microorganism or clumps of microorganisms that have
escaped an experimental animal host or some in vitro
reservoir (e.g. tissue culture flask or syringe). Infectious
aerosols may also consist of microorganisms that are
attached to inanimate particles, such as dust from animal
bedding. Larger aerosol particles (
5
m
m) often settle on
surfaces near the source, whereas smaller ones may travel
some distance before being deposited onto surfaces or
beinginhaled.Itisthisdissemination of contaminants that
contributes to secondary contact by people who work with
animals. Thus, personnel can become a major vehicle of
infection by touching contaminated surfaces and trans-
ferring the contaminant to him/herself and other people or
surfaces.
>
Mode of Transmission
To infect a worker, the infectious disease agent must leave
the nonhuman primate. Excretion in urine, saliva, and feces
and release through skin lesions are examples of natural
escape routes. Invasive research procedures such as ven-
epuncture, biopsy, surgery, and necropsy are obvious arti-
ficial avenues of escape. Tissues and body fluids removed
from animals may contain disease agents. Vectors present
on or having access to infected animals may also facilitate
the escape of disease-causing agents.
The most frequently documented modes of disease
transmission in animal research facilities involve contam-
inated needles and direct contact with infected animals.
These mechanisms account for 40% of all laboratory-
acquired infections resulting from documented accidents
(
Pike, 1976
). Animal bites, scratches, and injury on
contaminated work surfaces or cages should be included in
this category. However, aerosols, because of their easy
dissemination, are perhaps the most common
e
though
mostly undocumented
e
mode of transmission.
Aerosols are small particles of solids or liquids sus-
pended in air. Particles can become aerosolized by any
forceful activity and can remain airborne for an extended
time. Nonhuman primates produce aerosols simply by
their rapid movements and activity. Most husbandry
practices, such as using high-pressure water delivered via
a hose to remove animal waste from cages, pans, and
floors in animal rooms, produce aerosols, as do many
routine laboratory procedures such as centrifugation.
Workers may contribute significantly to aerosol produc-
tion. Vigorous removal of bedding from cages,
Route of Exposure
Infectious agents cause disease by four primary routes of
exposure: direct parenteral inoculation, inhalation, contact
with mucous membranes or broken skin, and ingestion. The
route of exposure for work-associated illness may be
the same or distinctly different from that associated with
the natural disease process.
The most common mechanisms of exposure to infec-
tious agents associated with experimental animal work are:
(1) direct inoculation by needles, cuts, or abrasions from
contaminated items with sharp edges, and via animal bites;
(2) contact of the mucous membranes of the eyes, nose, or
mouth by spills of contaminated materials, contaminated
hands, or contaminated surfaces; (3) ingestion; and (4)
inhalation of aerosols generated by accidents, husbandry
practices, and experimental manipulations.
Risk Assessment
The process of risk assessment requires a thorough
evaluation of a number of parameters including hazard
identification, dose
e
response assessment, exposure
assessment, and risk estimation and characterization. Each
of these steps is labor intensive, requires significant
research, and in the case of risk estimation may involve
historical, poorly documented information. A thorough
risk assessment provides the institution and the employee
with the best practices for prevention of exposure to
potentially harmful agents. A risk assessment requires the
involvement of personnel with a wide variety of
for
