Diseases Spread By Nuisance Wildlife Dr. Jorge Parada
- National Pest Management Association
Thursday, November 7, 2013
A Lesson in Prevention and Treatment
Whether hiking, camping, canoeing or
simply taking in the wonders of nature, many people enjoy spending
time outdoors all year round. However, while wondrous and
beautiful, being out in nature doesn’t come without risk –
especially if people come into contact with wildlife, which often
carry numerous infectious diseases.
Some of these “wildlife diseases” are well known (even though
they are not typically associated with wildlife) while others are
less known, but all are concerning when it comes to public
The plague or the “black death” is best known for ravaging
Europe during the Middle Ages and killing more than half the
population. However, the plague, while not widespread, still exists
in the United States. In fact, some of the highest number of
animals infected with the plague in the world are in the U.S. and
is most commonly found in the southwestern parts of the
This infection is caused by the bacteriaYersinia pestisand is
typically carried by the fleas found on rats, ground squirrels,
rabbits, prairie dogs and ferrets. In fact, entire prairie dog
colonies regularly are wiped out by outbreaks of plague.
In humans, the disease typically presents in two forms: bubonic
and pneumonic types. The bubonic form is characterized by a
bacteremia and infected lymph nodes (enlarged lymph nodes were
given the Latin namebulbus– from the Greekβολβόςorbolbós –and hence
the name bubonic plague). Human mortality in untreated cases of
bubonic plague is 25 to 60 percent. However, the pneumonic form
(pneumonic from pneumonia, or involving the lungs) is even more
dangerous. The pneumonic form is characterized by an acute
pneumonia and, unlike bubonic plague, is much more contagious and
rapidly fatal if untreated, with 100 percent mortality within one
to three days.
Veterinarians, hunters and ranchers have been killed by this
disease – often as a result of handling the carcass of a dead
animal or while trying to aid an injured/sick animal in which case
they are inadvertently bitten by an infected flea.
Immunization and avoidance of contact with fleas or animal
carcasses are the two best ways to avoid contracting this
potentially life-threatening infection. Active immunization may be
necessary for those people who partake in activities that increase
their exposure to wild animals and live in areas where the plague
is common. Additionally, avoiding contact with fleas and wild
animals is highly recommended. Hunters should use special
precautions in transporting dead animals.
Unfortunately, like the plague, rabies is also not uncommon in
the United States. The vast majority of rabies cases occur in wild
animals like raccoons, skunks, bats, and foxes. Transmission occurs
from bite wounds or any other situation where infected saliva gets
in cuts or skin abrasions (hence the common name for rabies“Bite
Wound Disease”). However, rabies can be transmitted through aerosol
transmission - breathing the air in areas where infected animals
reside, such as inside bat caves.
In wild animals, changes in behavior could come as a result of a
rabies infection. Odd behaviors such as a lack of fear of humans or
seeing typically nocturnal animals out during the day could be
cause for concern. While domestic animals once formed the largest
reservoir for the disease, since the 1960's, wildlife species have
become the leading carriers of rabies.
The disease is caused by the rabies
virus (Rhabdovirus), which infects the central nervous system,
the brain and ultimately causing death. The early symptoms of
rabies in people are similar to that of many other illnesses,
including fever, headache, and general weakness or discomfort. As
the disease progresses more symptoms appear such as anxiety,
confusion, paralysis, agitation, hallucinations, hypersalivation
(increase in saliva), difficulty swallowing, and hydrophobia (fear
of water). Death usually occurs within days of the onset of these
Unfortunately, once rabies disease has developed there is no
treatment and for practical purposes rabies is still considered 100
percent fatal. Thus, early preventive measures remain the only way
to guarantee survival after a bite by a rabid animal. Waiting for
symptoms to begin is a death sentence.
Again, immunization and contact avoidance are the two best ways
to prevent contracting this fatal infection. People who regularly
work with wildlife should be vaccinated against rabies. Otherwise,
the best protection for people and their pets is to avoid being
bitten. In case of a bite from a wild mammal, it’s important to
seek immediate medical care because rapid treatment with rabies
immunoglobulin (antibodies) and vaccination can block the infection
before it takes hold.
Unlike the plague or rabies, which have been well recognized for
many centuries, Hantavirus has only recently become recognized. The
name hantavirusis derived from the Hantan River area in South Korea, related to an outbreak of
Korean Hemorrhagic Fever among American and Korean soldiers during
the Korean War (1951-1953). This was later found
to be caused by a relatively newly discovered genus of viruses:
Hantaan virus. Still more recently, Hantavirus infections were
finally recognized in the United States. In 1993, an outbreak of
Hantavirus pulmonary syndrome occurred in the Four Corners region in the southwestern
United States (leading to the original name "Four Corners
disease”). The viral cause of the disease was found only weeks
later and was called the Sin Nombre virus ("Virus sin nombre",
Spanish for "nameless virus")
In the United States, deer mice (along with cotton rats and rice
rats in the southeastern states and the white-footed mouse in
the Northeast) are the vectors of the virus. These rodents shed the
virus in their urine, droppings, and saliva. The infection is
transmitted to people when they breathe air contaminated with the
virus which occurs when fresh rodent urine, droppings, or nesting
materials are stirred up and their particles become airborne.
The virus can also be transmitted through bites from infected
mice, albeit this transmission is less common. Researchers also
believe that people may be able to contract the virus after
touching something that has been contaminated with rodent urine,
droppings, or saliva and then touching their nose or mouth; or if
they eat food contaminated by urine, droppings, or saliva from an
Early onset of Hantavirus infection is nonspecific and includes
flu-like symptoms such as fever, cough, muscle aches, headache and
fatigue. However, the life threatening form of infection,
Hantavirus pulmonary syndrome, is characterized by a sudden onset
of shortness of breath with rapidly evolving pulmonary distress
that can be fatal in half the cases despite intensive care and
Anyone who comes into contact with rodents that carry Hantavirus
is at risk for infection. Rodent infestations in and around the
home, and structures in more rural areas such as cabins or barns as
well as campgrounds, put people at risk of Hantavirus exposure.
However, prevention and control is the primary strategy for
avoiding contact with infected rodents. People who live in areas
where Hantavirus is common should contact a licensed pest
professional to outline the best prevention plan and elimination
techniques in case of an infestation.
Tularemia, also known as “Rabbit Fever” as it is commonly
transmitted during the rabbit skinning process, is caused by the
Humans can become infected not only through contact with
infected animals or carcasses, but also as a result of the bite of
infected ticks, deer flies, and other insects. Transmission is also
possible through the inhalation of airborne bacteria and ingestion
of infected food or water. In the summer, most cases come from
infected tick bites. In the winter, cases are reported by hunters
who trap and skin infected animals. Landscape workers have also
been identified as a segment of the population who is at an
increased risk for tularemia infections. Person-to-person
transmission of tularemia does not occur.
The clinical manifestations, or symptoms, ofFrancisellainfection
may range from asymptomatic illness to septic shock and death, in
part depending on the virulence of the infecting strain, portal of
entry, inoculums (amount of bacteria a person is exposed to) and
the immune status of the host. A common type of tularemia is
ulceroglandular tularemia, which normally results from the bite of
infected ticks, or contact between broken skin andF.
tularensis(such as the blood of an infected animal when a hunter
skins a rabbit). A more rare and severe form of the disease,
pneumonic tularemia, is caused by inhalation of the bacteria.
Immediate treatment with the appropriate antibiotics is
recommended, as Tularemia can be fatal if left untreated.
Tularemia is found across the United States, but most cases are
in Missouri, Arkansas, South Dakota and Oklahoma.
Symptoms often appear abruptly three to five days after
infection, but can take as long as two to three weeks to appear.
While a fever is the most common symptom, others include joint
pain, chills, loss of appetite, and malaise. Infected people may
experience swollen lymph nodes, headache, chills, dry cough, sore
throat and ulcers at the site of infection, sore eyes, weakness and
There are several forms of tularemia, each specific to a
particular route of entry byF. tularensisinto the body.
Ulceroglandular tularemia is the most common form of the disease
and is accompanied by flu-like symptoms, ulcers at the site of
infection, and swollen lymph nodes.
Inhalation of the bacteria leads to pneumonic tularemia, the
most severe form of the disease. Pneumonic tularemia is
characterized by non-specific respiratory symptoms including
hemorrhagic inflammation of the lungs and bronchopneumonia. This,
in addition to low suspicion of tularemia (due to its relatively
low occurrence), makes it challenging for physicians to correctly
diagnose isolated cases.
Diagnosis is made on a combination of suspicious signs and
symptoms, followed by laboratory confirmatory testing. Treatment
typically requires intramuscular or intravenous antibiotic therapy
for 10 days.
Although these wildlife diseases are dangerous and pose a
significant risk to humans, they are not a reason to stop enjoying
the great outdoors. By following a few simple precautions, humans
can safely interact with wildlife and keep any health dangers at
Add Your Comments