After the Storm: Animal Health Risks

After a hurricane or tropical storm, the NC State Veterinary Hospital urges continued awareness of associated health risks posed to animals.

Among the health dangers are diseases transmitted by insects attracted to stagnant water, making those living in or near flooded areas particularly vulnerable. Owners are urged to keep animals away from standing water and to particularly avoid having horses drink or immerse themselves in standing water.

Here’s what animal owners should know about some of the most prevalent animal health risks after a hurricane’s wake.


The biggest leptospirosis risk factors for dogs in the United States includes drinking from rivers, lakes or streams.

What it is: Commonly affecting dogs, this bacterial disease often occurs in warm climates with high rainfall. According to the American Veterinary Medical Association, the biggest leptospirosis risk factors for dogs in the United States includes drinking from rivers, lakes or streams, roaming on rural properties and exposure to wild animals or farm animals. Some dogs develop the condition through interaction with infected urine.

What it looks like: Signs include fever, shivering, muscle tenderness and reluctance to move, says the AVMA, as well as vomiting, diarrhea, eye inflammation and loss of appetite. Dogs can develop difficulty breathing, nosebleeds, internal bleeding and swollen legs.

How it’s treated: Primarily with antibiotics. Recovery chances are good if it’s treated early and aggressively. Vaccines prevent leptospirosis for at least a year and an annual vaccination is recommended for at-risk dogs.

Impact on humans and other animals: Leptospirosis can spread from animals to people and cause flu-like symptoms and sometimes liver and kidney disease. Human infections are mostly the result of recreational water activities and infection caused by an animal is far less common.

Eastern Equine Encephalitis

What it is: Spread by mosquitoes, Eastern Equine Encephalitis, or EEE, causes brain and spinal cord inflammation in horses.  It primarily occurs in places with long hot and wet summers; most cases are reported in the late summer and early fall. It is a rare disease but is fatal in 90 percent of infected horses. North Carolina saw several cases of Eastern Equine Encephalitis this summer, but the number can vary wildly year to year.

What it looks like: Signs include fever, impaired vision, aimless wandering, leaning on structures and walking in circles. Horses may also have difficulty swallowing, may stumble when walking, have seizures or experience sudden death. It can take three to 10 days for EEE signs to appear.

How it’s treated: Vaccination is the most effective prevention tool. In North Carolina, horses should be vaccinated twice a year for all viral encephalitides, ideally in early spring and again in late summer or early fall.  Horses receiving these vaccinations for the first time should receive a second vaccination four weeks later and then a booster twice annually. Prevention measures for horse owners primarily involve reducing mosquito access to horses. Methods include placing fans inside barns to maintain air movement and managing standing water near horses and farm equipment. Mosquitoes can breed in a puddle that lasts longer than four days.

Impact on humans and other animals: Humans, other horses and birds cannot contract EEE directly from an infected horse, though infection may occur from the bite of an infected mosquito. Humans are rarely infected with EEE and exposure risk is minimized by using insect repellent and covering exposed skin, especially during outdoor activities at dusk and at night when mosquitoes are most active.


What it is: Caused by a water-borne parasite, pythiosis typically impacts the skin of the limbs and abdomen in horses, and the skin and gastrointestinal tract of dogs. Infection can also settle in the brain, sinuses and lungs. Animals may contract the disease through swimming or wading in standing water in pastures, swamps, ponds, wetlands or lakes. Horses with limb wounds and access to standing water in their pasture may be at increased risk for developing this disease.  The parasitic spores that cause pythiosis usually thrive in tropical and subtropical waters, but the disease is seen in North Carolina, often after hurricanes or unusually rainy seasons.

What it looks like: In dogs, the most common sign is weight loss; dogs can become extremely thin. Other signs in dogs include vomiting, diarrhea, and ulcerated nodules of the skin that do not heal. In horses, ulcerated, draining masses are most commonly seen on the lower limbs or ventral abdomen, but can also involve the head, neck or respiratory tract.  The lesions often have hard yellowish granules or “kunkers” within them and can be extremely itchy.  Infections of the lungs, brain and sinus can cause fever, coughing and sinus swelling.

How it’s treated: Treatment is most effective when the signs of pythium are caught early. Early treatment includes aggressive surgical removal of compromised tissue, repeated wound cleaning with antiseptics such as chlorhexidine or betadine solution, and antifungal therapies, both local and systemic depending on severity. Hospitalization is recommended in advanced cases to allow for daily debridement (removal of devitalized tissue and “kunkers,” yellow, firm granules of dead tissue) and intensive wound care. Vaccination has also been shown to reduce the size of lesions, particularly in early stages of the disease.

Impact on humans and other animals: Pythium infection occurs when the spores come into contact with an open wound in a moist environment. Therefore, all domestic animals including dogs, cats, horses, cattle, sheep, and goats are at risk of pythiosis. Human cases are rare in the United States, but have been reported following contact of an open wound in contaminated water.

Heartworm disease

Once an animal is bitten by infected mosquitoes, larvae mature to adult heartworms in about six months.

What it is: A heartworm is a parasite primarily infecting dogs, cats and ferrets. It can only be transmitted from animal to animal by mosquitos. Infected animals cannot directly give other animals heartworms. Once an animal is bitten by infected mosquitoes, larvae mature to adult heartworms in about six months. They move through an animal’s body, growing up to 14 inches in length. They find homes in the heart, reducing its ability to pump blood. They can lodge in the lungs and damage blood vessels. When worms become adults, the condition becomes heartworm disease. Adult worms can breed and produce young heartworms called microfilariae. All dogs and cats are at risk for heartworm infection, though, unlike a dog, an infected cat is unlikely to transfer an infection to another mosquito.

What it looks like: According to the AVMA, dogs recently or mildly infected may not show signs until adult worms develop. Dogs may become lethargic, experience loss of appetite, cough or have difficulty breathing. Dogs may tire rapidly even following moderate exercise. Signs of heartworm disease in cats include coughing, vomiting and respiratory distress, though diagnosing an infection in cats is more difficult than it is with dogs, says the AVMA.

How it’s treated: Heartworm is a life-threatening disease and steadfast prevention is key. An array of medication options approved by the Food and Drug Administration are available to pet owners and veterinarians can recommend the best methods for individual pets. Preventatives do not kill adult heartworms, eliminate an infection or prevents signs of the disease. The American Heartworm Society recommends testing for heartworm yearly and administering heartworm preventatives monthly.

Veterinary treatment for heartworm disease is primarily drug injections or other prescription medication. Severe cases may require surgery and require hospitalization. Exercise will need to be restricted.

Impact on humans and other animals: Human infection is very rare and, even then, only typically leads to mild health issues.

Equine West Nile Virus

What it is: Also known as West Nile Encephalitis, the disease is transmitted by mosquitoes and other insects that carry the pathogen from infected birds to the horses they then subsequently bite as well. West Nile Virus was first recognized in the Western Hemisphere in 1999, according to the American Association of Equine Practitioners.

What it looks like: Equine West Nile Virus causes inflammation of the brain and spinal cord. According to the Equine Disease Communication Center, clinical signs include fever, lack of appetite and lethargy. Onset of neurological signs is often sudden, according to the EDCC, and begins with periods of hyperexcitability, followed by apprehension and drowsiness. Conditions such as tremors, facial paralysis, limb incoordination, colic and inability to stand can also be seen. Mortality rates for West Nile viral infection in horses is approximately 40 percent, with supportive care improving the chance of survival for affected horses.

How it’s treated: There is no cure; keeping vaccinations up to date is key. In North Carolina, horses should be vaccinated twice a year for all viral encephalitides, ideally in early spring and again in late summer or early fall.  Horses receiving these vaccinations for the first time should receive a second vaccination four weeks later and then a booster twice annually. Treatments for a horse with West Nile encephalitis include anti-inflammatory medication, intravenous fluids and nutritional support, according to the American Association of Equine Practitioners (AAEP).

Other than vaccination, horse owners can reduce the West Nile Virus risk by reducing mosquito breeding sites, especially areas of standing water where horses congregate. Insect repellent should be used frequently, horses should be kept in at night and equipment in which standing water can accumulate should be removed.

Impact on humans and other animals: A horse with West Nile Virus is not contagious and cannot infect other horses. Humans contract West Nile Virus from mosquitoes, not from horses.

If you believe an animal is displaying any symptoms of these diseases, contact your primary care veterinarian immediately.

Further resources:

The NC State Veterinary Hospital

The American Veterinary Medical Association

The North Carolina Veterinary Medical Association

The NC State Equine Veterinary Service

The North Carolina Department of Agriculture and Consumer Services Veterinary Division

The Centers for Disease Control and Prevention’s guide to mosquitoes and hurricanes

As we cope with the devastation caused by hurricanes, we can make a difference together, too. A donation to the CVM’s Disaster Relief Fund will continue to help animals that have been rescued and sheltered. Thank you for your support.