Animal Related Diseases

There are several diseases in Colorado that can transmitted from animals to humans such as West Nile Virus, Rabies, Hantavirus Pulmonary Syndrome, Plague, Tularemia, Colorado Tick Fever, and Western Equine Encephalitis. For further information on education, prevention, and case data in Colorado please visit CDPHE Animal-related Diseases. Check out some of the videos below on Colorado animal-related diseases from our neighbors at Summit County Environmental Health. 

West Nile virus is most commonly spread through the bite of an infected mosquito, however there have been few cases of the spread of the virus through blood transfusions, organ transplants, and from mother to baby during pregnancy or at the time of birth. Anyone is at risk of getting West Nile virus, but few are likely to develop serious illness. Serious illness can include meningitis or encephalitis which starts with a high fever and headache and may progress to stiff neck, disorientation, tremors and coma. Those at higher risk, including those over 50 and the immunocompromised, may experience permanent brain damage or death. There is no treatment nor a vaccine for West Nile virus. West Nile virus is a communicable disease and must be reported by the medical community (hospitals, physicians, laboratories) to local and state health departments. In Grand County for questions or concerns about West Nile virus please reach out to Michelle Mitchell, RN emailing to mmitchell@co.grand.co.us or by calling at (970) 725-3288.

The state of Colorado has had cases of West Nile virus every year since 2002. Most reports of West Nile virus in humans in Colorado occur in August and September, however the mosquitoes can be active from May to October. The percentage of birds and mosquitoes infected is small and the chances of getting bit by an infected mosquito will increase as the continuing summer season allows the infection of more birds and mosquitoes. The 2022 season reported West Nile virus in mosquitoes in Boulder, Larimer, and Weld counties. See the video from Summit County on how mosquitoes are harvested for testing. Data on West Nile virus in Colorado can be found at West Nile virus data | Department of Public Health & Environment (colorado.gov). Grand County has only had 2 reported cases of West Nile virus in humans, one in 2003 and one in 2021. Despite this, it is still important to take actions to protect yourself and your loved ones. Use a repellent that contains DEET, picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol products and spray on exposed skin as well as any clothing thin enough for a mosquito to penetrate. Empty any still water puddles that could harbor mosquito larvae and ensure windows and doors have screens. If you can stay indoors during dusk through dawn you can miss when mosquitoes are most active.


Rabies is transmitted from a mammal to another mammal through direct contact with saliva or brain/nervous system tissue. This direct contact is most commonly a bite, but can also be a scratch or open wound that comes in contact with infectious material. Contact with a rabid animal’s blood, urine, or feces is not associated with a risk of infection, as well as, petting. Any mammal can give and receive rabies. In the United States the mammals that most commonly carry rabies are wild animals including raccoons, skunks, foxes, and bats. A bite or scratch from a bat is very small and often hard to discover. If treatment is not initiated soon after the exposure the result can be fatal. For these reasons, the leading cause of human rabies deaths in the United States is exposure to an infected bat with 7 out of 10 of human rabies deaths associated with infection by bats. Domestic animals including livestock and pets may become infected with rabies if they are allowed contact with wildlife. Dogs account for only 1% of rabid animals in the United States due to vaccination laws. However, dogs are still the main cause of human rabies deaths in many other countries. 

Vaccinations provide immunity for at least 3 years. If not vaccinated, rabies infection can be prevented through post-exposure prophylaxis or PEP. If you are able to safely catch or kill the animal that bit you the animal can be examined for rabies and if it is negative for rabies infection treatment is not necessary. If the animal is wild and/or if there are suggestive signs of rabies then it should be euthanized and shipped for examination. If the animal is domestic or a stray it can be confined and observed for 10 days for signs of rabies infection. Wild animals should not be confined and observed because the length of time when symptoms appear is not well known for these animals. 

There are ways you can protect yourself and your family and/or pets including vaccinating your pets and keeping cats indoors and dogs under supervision while outside. Do not interact or allow your pet to interact with wildlife and call animal control to handle any wildlife or strays. Colorado is home to bats which are the leading cause of human rabies deaths. Bat-proofing your house can help protect against bat bites. In order to bat proof your house you first need to identify possible spots a bat could enter from like those in the picture adjacent. Using window screening or other material to block these entrances is an effective way to keep possibly infected bats out of your home. Bats have tested positive for rabies in Grand County. Use this link: Historical rabies data | Department of Public Health & Environment (colorado.gov) in order to see where rabid animals were found in Colorado from 2019 through 2022.

If you have been scratched or bitten by an animal, wash the site immediately with soap and water. Plan to see a healthcare provider as soon as possible in order to decide if you require treatment. This decision is based on the type of exposure and animal as well as if the animal is available for testing. If you are not sure that you were bitten or if you find a bat where you were sleeping assume you have been bitten. Relay the incident to Animal Control: 970-887-2988. Rabies is a communicable disease and must be reported by the medical community (hospitals, physicians, laboratories) to local and state health departments. In Grand County for questions or concerns about rabies please reach out to Michelle Mitchell, RN emailing to mmitchell@co.grand.co.us or by calling at (970) 725-3288.

Hantavirus in humans is commonly caused by the inhalation of airborne urine, droppings and bedding from an infected rodent. Transmission can also occur if urine, dropping, or saliva from the infected rodent are on food or a hand used to touch your face. It is also possible to get hantavirus from a bite from an infected rodent, however this is rare. The deer mice are common carriers of hantavirus, but other carriers include the cotton rat, rice rat, and white-footed mouse. There is no way to tell if a rodent has hantavirus so all contact with rodents should be avoided. 

            There are different hantaviruses with the most common in Colorado being the Sin Nombre virus that is found in deer mice. From 1993-2021, there were 119 confirmed cases of hantavirus Pulmonary Syndrome in Colorado residents, with 2 of these coming from Grand County. This virus has a mortality rate of 38% and there is no specific treatment or vaccine for a hantavirus infection. Symptoms of infection can start at variable times. After 1 to 8 weeks early symptoms will include fatigue, fever, and muscle aches, and about 50% of people will experience headaches, dizziness, chills and abdominal problems as well. After this initial phase the late symptoms will include coughing and shortness of breath due to the lungs filling with fluid. This respiratory distress stage is in which patients die so it is important to receive healthcare as soon as you feel shortness of breath and suspect you may have had exposure to rodents. Patients that have not started severe respiratory distress can be intubated and given oxygen therapy to help them through the distress, but if the patient arrives already experiencing full distress the treatment is less likely to be effective. Hantavirus is a communicable disease and must be reported by the medical community (hospitals, physicians, laboratories) to local and state health departments. In Grand County for questions or concerns about hantavirus please reach out to Michelle Mitchell, RN emailing to mmitchell@co.grand.co.us or by calling at (970) 725-3288.

            Anyone can be at risk of becoming infected with hantavirus. Activities that increase your chance of exposure to rodents or their secretions include opening and cleaning previously unused buildings, house cleaning activities, and camping/hiking. Any activity or place that carrier rodents are known to live at should be considered a place of possible exposure so precautions should be taken. Precautions include wearing a mask and gloves while sweeping unused buildings and cleaning the area using measures that keep the dust from becoming airborne. Take a look at the adjacent video from summit county about exactly how you can clean up droppings without making them airborne.

Tularemia in humans has not been documented during Colorado surveillance between 2012- 2020 in Grand County, although there have been 102 cases in the state of Colorado. Just because Grand County does not have as many tularemia cases, you can still be at risk, especially if you travel. Our neighboring counties, including Summit County have documented animals infected with tularemia in recent years. Take a look at Summit County’s video for a quick overview of tularemia. 

Tularemia is a potentially serious illness that is caused by the bacterium Francisella tularensis. This bacterium is commonly called “rabbit fever” because it is usually found in rabbits, rodents, and hares, but can be found in other animals, like cats. There are multiple ways that you can be exposed to this bacterium and pathway of exposure may affect the symptoms experienced. No matter which form of tularemia, it is usually accompanied by fever. Tick or deer fly bites can expose you to F. tularensis and result in tularemia taking the form of ulceroglandular or glandular tularemia. Ulceroglandular tularemia is the most common form of tularemia in which a skin ulcer appears at the site where the bacteria entered the body accompanied with swelling of regional lymph glands, usually in the armpit or groin. Glandular tularemia is similar to ulceroglandular except there is no ulcer. The bacterium can also be transmitted via the skin if you handle any infected animal tissue which can result in glandular, ulceroglandular, and/or oculoglandular tularemia. Oculoglandular tularemia is from exposure through the eye and includes irritation and inflammation of the eye and swelling of the lymph glands in front of the ear. Exposure can also occur by eating under-cooked infected animals or drinking contaminated water and would cause oropharyngeal tularemia. Oropharyngeal tularemia may cause a sore throat, mouth ulcers, tonsillitis, and swelling of lymph glands in the neck.  One rare form of tularemia occurs when one inhales dust or aerosol contaminated with F. tularensis which causes pneumonic tularemia. Pneumonic tularemia is the most serious form and includes coughing, chest pain, and difficulty 

Colorado is home to about 30 different species of ticks. The most common species in Grand County is the Rocky Mountain wood tick. The Rocky Mountain wood tick is the most reported tick that bites humans and dogs in Colorado. Despite this, the Rocky Mountain spotted fever that this tick and many others may carry, is still quite rare in Colorado. Rocky Mountain wood ticks are most active and do most biting in spring, becoming dormant with warm weather in summer. Tick activity usually peaks in spring and early summer, but some ticks can be active throughout the year.

            Colorado Tick Fever is the most common tick–borne illness in Colorado. CTF is a viral disease that comes from the bite of an infected Rocky Mountain wood tick. Ticks can pick up this virus when they feed on the blood of a reservoir animal. Reservoirs for CTF include rodents such as squirrels, chipmunks, and mice. The time from tick bite to onset of illness for Colorado tick fever ranges from about 1 to 14 days. Symptoms depend on the patient and can range from mild to severe. The most common symptoms are fever, chills, headache, body aches, and feeling tired. About half of patients have a biphasic fever in which they have several days of fever, feel better for several days, then have a second shorter period of fever and illness. Some cases experience a sore throat, vomiting, abdominal pain, or a skin rash. In severe cases the illness may affect the central nervous system that can display as a stiff neck and confusion, but deaths due to CTF are rare.

CTF virus can remain in red blood cells for several months, so blood and bone marrow should not be donated for 6 months following infection. Colorado Tick fever is not transmitted from person to person unless through a blood transfusion. There are no medications to prevent or treat CTF and the only treatment is plenty of rest and fluids and over-the-counter pain medications. Colorado Tick Fever is a communicable disease and must be reported by the medical community (hospitals, physicians, laboratories) to local and state health departments. In Grand County for questions or concerns about Colorado Tick Fever please reach out to Michelle Mitchell, RN emailing to mmitchell@co.grand.co.us or by calling at (970) 725-3288.

            Most cases of Tick-borne Relapsing Fever are transmitted through the bite of soft ticks in the Ornithodoros family. Ornithodoros hermsi prefers coniferous forests at altitudes of 1500 to 8000 feet where it feeds on tree squirrels and chipmunks. There was only one known case of Tick-borne Relapsing Fever in a Colorado resident during surveillance between 1990-2011. Soft ticks like Ornithodoros hermsi commonly come into contact with humans when they sleep in rodent-infested cabins. Soft ticks live in rodent burrows and emerge at night to feed briefly on people before returning to their burrows. The bite of a soft tick is brief and most people do not know that they have been bitten. Tick-borne Relapsing Fever is caused by the TBRF bacteria and is characterized by a fever lasting roughly 3 days, followed by 7 days of no fever, and then another 3 days of fever. Other symptoms include headaches and muscle and joint aches. Antibiotics are used to treat Tick-borne Relapsing Fever. Tick-borne Relapsing Fever is a communicable disease and must be reported by the medical community (hospitals, physicians, laboratories) to local and state health departments. In Grand County for questions or concerns about tick-borne relapsing fever please reach out to Michelle Mitchell, RN emailing to mmitchell@co.grand.co.us or by calling at (970) 725-3288.

Rocky Mountain spotted fever is a bacterial disease spread through the bite of an infected, in Colorado, Rocky Mountain wood tick. Symptoms include fever, headaches, nausea, vomiting, stomach pain, muscle pain, lack of appetite, and a rash. Almost all patients with RMSF will develop a rash, however it often does not appear early in illness. Rash usually develops 2-4 days after fever begins and can vary widely over the course of illness. Some rashes look like red splotches and some look like pinpoint dots. If RMSF is not diagnosed and treated early with the antibiotic Doxycycline, it can progress to a serious illness in which acute illness can leave you with permanent damage or death. Damage to blood vessels can result in amputation of arms, legs, fingers, or toes and hearing loss, paralysis, or mental disability. 

Tularemia is also a tick-borne illness, read above under Tularemia for more information on tularemia.

            Preventing these illnesses means preventing exposure to ticks. Use these tips to keep yourself safe from Tick-Borne Illnesses

  • Apply Environmental Protection Agency (EPA)-registered insect repellents to any exposed skin or thin clothing. You can also treat clothing and gear with permethrin.
  • Avoid wooded and brushy areas with high grass and leaf litter by staying in the center of trails.
  • Check your clothing, pets, and body for ticks after being outdoors and shower soon after being outdoors if possible.
  • Ask your veterinarian about the appropriate tick prevention product for your pets that may spend time in close contact with ticks.
  • Clear leaf litter and tall grasses from your yard to encourage a Tick-safe Zone in your yard. More steps to fortify your yard can be found on Preventing ticks in the yard | Ticks | CDC
  • When removing a tick that has bitten you use clean, fine-tipped tweezers to grab the tick as close to the skin’s surface as possible and pull upward with steady, even pressure. If mouth-parts break off remove these with the tweezers and if you are unable to remove the head leave it alone and allow the skin to heal. Clean the bite area and your hands and dispose of any live ticks by putting it in alcohol, in a sealed bag/container, by wrapping it tightly in tape or by flushing it down the toilet.
  • Prevention of Tick-borne Relapsing Fever specifically includes avoiding sleeping in rodent-infested buildings whenever possible. If you own a cabin identify and remove any rodent nests from walls, attics, crawl spaces, and floors. Treat “cracks and crevices” in the walls with pesticide and establish a pest control plan to keep rodents out of your cabin.