Diseases and Wildlife: Implications for Nebraska
by Barb Ogg, Ph.D., Extension Educator,
University of Nebraska Cooperative
Extension in Lancaster County
and Wayne Kramer, Ph.D., Medical Entomologist, Nebraska
Department of Health and Human Services
diseases having a wildlife connection, Lyme disease, hantavirus,
and West Nile virus are more and more frequently in the news.
What is the current status of these diseases in Nebraska? Wayne
Kramer is Nebraska's lead investigator of these vector-borne
diseases. He is a medical entomologist with the Nebraska Department
of Health and Human Services, Regulation and Licensure. This
article discusses how these diseases may potentially impact
disease is the most reported vector-borne disease in the U.S.
It is caused by a bacteria, Borrelia burgdorferi, and
was first identified in Lyme, Connecticut in 1982, although
it likely has been present in the U.S. since the 1800's. It
is a chronic debilitating disease, but rarely fatal. More than
16,000 cases of Lyme disease were reported in the U.S. in both
1998 and 1999, and the greatest number of cases continues to
occur in northeastern, mid-Atlantic, and northcentral states
(Minnesota and Wisconsin). A distinctive, expanding circular
rash is the best early symptom of the disease and occurs in
60 to 80 percent of all cases. Lyme disease is maintained in
nature in a cycle involving Ixodes scapularis, the deer
tick, and associated reservoir hosts (white-footed mice and
1996, a related bacteria, Borrelia lonestari, was isolated
from the lone star tick, Amblyomma americanum, which
has a distribution in the southern U.S. including Nebraska.
This fact may help us better understand the current status of
Lyme disease in Nebraska. A relatively small number of cases
of Lyme disease have been reported in Nebraska (84 for the period
of 1990 to 1999) despite the fact that the only known competent
vector of Borrelia burgdorferi, the deer tick (I.
scapularis), has not been found here. The majority of the
Lyme disease-like illnesses that are being reported and counted
as classic Lyme disease in Nebraska may, in fact, be caused
by B. lonestari. Also, most cases of the Lyme-like disease
were contracted in the southeastern part of the state which
overlaps the lone star tick geographical distribution—good epidemiological
evidence this tick may be the vector.
is a human vaccine currently being marketed for Lyme disease
but it is not recommended for Nebraska residents. Because the
risk of Lyme disease is very low in Nebraska and because vaccines
have a high degree of specificity, it is thought the vaccine
would not protect persons against B. lonestari.
lone star tick is also known to transmit another bacterial agent,
Ehrlichia chaffeensis, which causes human monocytic ehrlichiosis
(HME). This bacteria was first described in 1986, and one case
has been reported in Nebraska. The spectrum of human disease
ranges from an illness that is very mild to a severe, life threatening,
or fatal disease. The disease may be confused clinically with
Rocky Mountain spotted fever. The wildlife reservoir for this
disease is also the white-tailed deer.
at the Lancaster County Extension Office, have the expertise
to identify tick species. During the summer of 2000, we were
surprised to identify several deer ticks. However, each of these
ticks were brought back to Nebraska by folks traveling in the
eastern part of the U.S. So, if you are vacationing in areas
where deer ticks occur, check yourselves carefully for the presence
of ticks. If the populations are very high, consider using the
repellent DEET or the insecticide permethrin on your clothing.
Pulmonary Syndrome (HPS):
is a deadly respiratory condition caused by a virus named the
Sin Nombre virus. It is carried by a rodent, primarily the deer
mouse (genus Peromyscus). HPS was first identified in
1993 in the Four Corners region of the southwest after several
individuals died, but the disease has been documented as far
back as 1959. It is a rare disease—as of February 2001, 279
cases were confirmed in 31 states. Cases are concentrated in
western states, although cases have been documented as far east
as Rhode Island and New York. Only one case of HPS has been
documented in Nebraska (1999), even though surveys of rodent
populations show that the Sin Nombre virus is endemic in deer
mice populations throughout Nebraska. In a number of surveys,
between four and 20 percent of collected rodents carried the
Sin Nombre virus.
is no insect vector for hantavirus. The risk associated with
this disease is solely dependent on factors that promote rodent
populations and the frequency of human activities in infested
areas. Rodents are completely unaffected by the disease and
do not get sick or die, but serve as a reservoir and can infect
other rodents. The virus is shed by rodents in the urine and
feces and may remain viable in the environment for some period
risk to humans occurs when individuals inhale infectious virus
particles. Many human exposures have come from contaminated
buildings, occupying previously vacant cabins, cleaning barns
and other outbuildings, but other sources of exposure have been
associated with agricultural activities, such as planting and
harvesting field crops. Hikers and campers may also encounter
there is always a risk, even though it is small, precautions
should be taken to prevent exposure to the virus. Wearing a
properly fitted respirator with a HEPA filter will provide protection
by effectively filtering out the tiny virus particles which
may be airborne. Paper dust masks do not provide effective protection.
When dealing with rodent-infested areas, one must first reduce
rodent populations, ventilate the area before cleaning, and
then use wet cleaning techniques (see Safely
Clean Up After Rodents). These steps will reduce the
risk from inhaling infectious virus particles.
Nile encephalitis, thought to be first introduced into New York
City in 1999, was found in four states by the end of 1999. In
2000, it expanded further outward from the New York City metro
area to 12 states. The virus circulates in nature in a mosquito-bird
cycle and clinical disease is known in humans and horses. Although,
most bird species are not affected by the virus, a small number
of bird species are debilitated by this disease; the most susceptible
birds belong to the family Corvidae (crows, ravens, jays). The
observation of dead crows (Corvids) which later tested positive
for West Nile virus has been a useful surveillance tool to monitor
the expanding range of this virus in both 1999 and 2000 on the
east coast. The dead crows are more likely to be single crows,
rather than a large flock, which is more likely to indicate
mortality from a toxic substance, like a pesticide.
people who are infected with the West Nile virus have no symptoms
or experience a mild illness (fever, headache, body aches) and
fully recover. Some individuals, particularly the elderly, West
Nile virus can cause encephalitis and cause permanent neurological
damage to the brain and can be fatal. Symptoms include a severe
headache, muscle weakness, high fever, stiff neck, confusion,
and loss of consciousness (coma).
is the likelihood that the West Nile virus will get to Nebraska?
Based on the expansion of the disease from 1999 to 2000, a good
guess is that the disease could reach Nebraska in two to five
years. Predictions are complicated because each geographical
area has its own complement of mosquito species that may or
may not be good vectors.
you live in Nebraska and find dead crows, you are urged to call
Wayne Kramer (402) 471-0506. To be useful for analysis, the
crows must be recently dead and in reasonably good condition.
The West Nile virus cannot spread directly from birds to people.
However, dead birds should not be handled with bare hands. Use
gloves to place the dead bird in a double plastic bag.
the state be ready for all the testing and monitoring if the
West Nile encephalitis gets to Nebraska? The CDC has granted
$90,000 to the Nebraska Department of Health and Human Services
to develop the laboratory testing procedures that will be needed.
that have a wildlife connection are not new, but increased human
activities where wildlife are abundant have increased the risk
of contracting Lyme disease and HPS. As we continue to spend
time outdoors, exposure to these diseases will continue.
the other hand, West Nile encephalitis is a new disease to North
America being introduced into the United States via infected
wildlife or mosquitoes from Africa, Eastern Europe, or West
Asia. This may be an unfortunate consequence from increased
international activities and trade. These diseases and recent
livestock diseases in the news (foot and mouth disease and mad
cow disease) remind us how small the world really is.
Clean up After Rodents
rodents from your home/cabin or other dwelling will decrease
your risk for Hantavirus Pulmonary Syndrome. Follow these
standard rodent removal and cleanup guidelines:
Set spring traps that will kill mice.
Use rubber gloves and spray the nest or dead rodent until
soaked with a household disinfectant solution or three
tablespoons of bleach in one gallon of water. Other disinfectants
can also be used as directed. Let the area soak thoroughly
10 to 15 minutes.
Remove the nest or rodent using a long-handled shovel
or rubber gloves.
Double bag the rodent or nest securely with plastic bags
and dispose of them in the trash. Persons in rural areas
may bury the waste two to three feet deep.
Clean up the rodent area and traps by spraying with disinfectant
solution. Let the area soak for 10 to 15 minutes. While
still wearing gloves, wipe up the area with paper towels
Double bag all paper towels, rags, and gloves used in
the cleanup. Dispose of them in a tightly covered trash
Wash your hands with soap and water after completing the
cleanup. After the rodents are removed, floors, countertops,
cabinets and other surfaces should be cleaned with a solution
of three tablespoons of household bleach in one gallon
of water, or by a commercial disinfectant. Do not sweep
floors with a broom, or vacuum, until area has been disinfected.
can be steam cleaned; dirt floors should be sprayed with
a disinfectant solution.
Department of Health and Human Services
June 5, 2002
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