Algal blooms sicken people, animals across United States

The first data from a three-year federal surveillance program indicate harmful algal blooms sickened and killed hundreds of animals.

From 2016-18, the 18 states participating in the Centers for Disease Control and Prevention’s surveillance program reported algal blooms sickened at least 389 people and 413 animals, according to the Dec. 18 issue of the CDC’s Morbidity and Mortality Weekly Report. All of the people survived, but 369 of the animals died.

Three-quarters of the animal illnesses occurred among wildlife, including 300 birds killed by a single freshwater bloom during May 2018 in California. Among domesticated animals, the blooms sickened at least 50 dogs, two cats, 36 cattle, four poultry, and two equids, according to the report.

Virginia Roberts is an epidemiologist in the Waterborne Disease Prevention Branch of the CDC National Center for Emerging Zoonotic and Infectious Diseases and lead author of the new report, and she is leading the CDC’s One Health Harmful Algal Bloom Surveillance Working Group. As the project expands, she expects it will help show where blooms and illnesses occur, characteristics of the blooms themselves, and the effects on humans, domesticated animals, and wildlife.

The surveillance covers harmful blooms caused by subsets of algae and cyanobacteria in fresh water and salt water, according to the report. The blooms can be exacerbated by nutrient pollutants, such as phosphorus used in fertilizer, and rising water temperatures resulting from climate change.

Less than 1% of algal blooms produce toxins, and some blooms can be beneficial food sources, although even blooms without toxins can create anoxic conditions in water, block light to other organisms, and harm or clog fish gills, according to the National Oceanic and Atmospheric Administration.

In addition to causing illness through direct exposure, some of the toxins can accumulate in the food chain and cause seafood-related poisoning, Roberts said. Coastal blooms also can aerosolize toxins, as seen when people near red tides in Florida developed coughs and sore throats.

Blooms that are harmful, Roberts said, produce a wide range of toxic substances with varied effects on animals.

“We’re concerned about the health impacts of those individual toxins and how they might mix together,” she said.

The CDC report indicates diagnostic tests for harmful algal bloom toxins are unavailable for routine clinical settings in human and animal medicine, so less than 5% of human or animal illnesses were confirmed.

Roberts said the states early to adopt the surveillance collected and provided data using their own methods and priorities. The figures collected so far show that people and animals are becoming ill across the country, she said.

“It takes a lot of work to conduct this type of surveillance and other types of public health surveillance,” she said. “You have to have the capacity to detect, investigate, and report these types of events.”

It also requires awareness of the risk of blooms and the need to report illnesses to public health authorities.

Dr. Katharine Benedict, veterinary epidemiologist in the Waterborne Disease Prevention Branch, said veterinarians can help improve the data collection when they know whether blooms are a problem in their area, collect good information on patients with known or suspected recent exposures to fresh or marine waters, and give state or local health departments information on those exposures.

About 90% of the blooms recorded in the first three years of surveillance occurred in fresh water, and people described visible scum in 39% of blooms, the CDC report states. The blooms peaked in July, and animal illnesses occurred May through September.

Dr. Benedict said veterinarians may be able to use data from the project in deciding whether to include harmful algal bloom toxicosis among their differential diagnoses. Although the signs of toxicosis can be nonspecific, identifying which are most common in pet or livestock species can help veterinarians understand how the blooms are affecting their patients, she said.

Among animals with clinical signs of illness, two-thirds had generalized signs such as weakness, lethargy, and anorexia, the report states. Half had gastrointestinal illness, and one in seven developed neurologic signs such as seizures and stumbling. Time to onset ranged from 15 minutes to four days.

Twenty-five animals received veterinary care.

Roberts and Dr. Benedict recommend that veterinarians in areas with harmful blooms teach pet or livestock owners how to prevent exposures and respond if their animals have been exposed. When dogs jump into water with a visible bloom, for example, the owners should wash them with tap water to stop them from ingesting the toxins as they lick their fur.