Moose Die-Off Triggered by Climate Change Brainworm, Liver Flukes and Winter Ticks [Video]

Moose die-off blaimed on climate change, brain worm, liver flukes and winter ticks
The latest tumble in moose numbers throughout North America is suspected to be linked to climate change, alongside a number of parasitic conditions

A great mystery is currently plaguing scientists, who are watching the ever-spiraling population of moose with grave concern. Throughout North America, the moose population seems destined to dwindle to hapless numbers.

Parasitic conditions, including brainworm, liver flukes and winter ticks, are all thought to contribute towards the disastrous fall of these iconic North American creatures. Recent hypotheses even implicate climate change in the phenomenon.

Moose Tracking Efforts

Researchers are now tasked with tracking moose populations, in a desperate attempt to understand the majestic creatures’ collective plight. These teams are attuned to ominous text message alerts, signaling the possible demise of yet another moose, whether it be the early hours of the morning, or the final throes of the evening. They dread to read the disheartening words, “mortality event detected.”

Moose deaths are, invariably, hard to study. The moose is a lonesome creature that does not travel as part of a herd, making scientists’ endeavors to follow their movements somewhat of an arduous task. This is only worsened by the rate at which Moose decompose. As moose are comprised of large amounts of adipose tissue, they putrefy at an accelerated rate, whilst scavenging animals within woodland habitats also help to make light work of these lifeless carcasses.

Minnesota initiated a program that sought to trace the location of individual creatures, upon their demise. Investing $1.2 million into sophisticated technology that was capable of achieving this ambitious goal, large numbers of moose were rounded up and tagged with special collars, providing researchers with accurate GPS positioning of each subject. The beasts were also non-invasively implanted with transmitters that measured their heart rates and body temperatures.

Moose are being tracked with collars and transmitters
Researchers are tracking the deaths of moose, using GPS positioning and heart rate monitors, in a bid to explain their dwindling numbers

The moose population of Minnesota, particularly within the northeastern sectors of the state, is in a particularly bad way, with a mortality rate that surpasses all other states. The numbers in Minnesota have plummeted to about a third of the figure recorded in 2009. According to the National Wildlife Federation, the northeast Minnesota population of moose has crashed by 35 percent, since last year alone, leaving fewer than 3,000 still alive.

In the event that a moose’s heart stops beating, a text message alert is dispatched to awaiting researchers. Precise coordinates are provided to retrieval teams, who are then deployed to scoop up the moose, so as to determine its likely cause of death.

The commissioner for the Department of Natural Resources, Tom Landwehr, had the following to say:

“This is further and definitive evidence the population is not healthy. It reaffirms the conservation community’s need to better understand why this iconic species of the north is disappearing from our state.”

As a result, all moose hunting has been suspended, with the number of moose permits falling quite drastically.

Meanwhile, journalists from OnEarth teamed up with David Pauly, a man who has been working with the Department of Natural Resources (DNR) since his career first began, to gain first-hand experience of a moose retrieval expedition.

After having received one of the afore-mentioned text message alerts for one of their tagged moose subjects, the group, led by Pauly, stumbled across the poor creature, suffering and completely immobilized. The animal’s body was riddled with winter ticks; whether this was the sole reason for its desperate state remained unclear.

A saddened Pauly was then forced to euthanize the moose.

White-Tailed Deer, Gastropods and Brainworm

The Wildlife Health Program of the Minnesota DNR has identified a number of diseases that the moose has become susceptible to.

Brainworm (Parelaphostrongylus tenuis) is the disease that most associate with moose. Approximately 60 percent of all public reports of moose ailments were the result of moose

Life cycle of brainworm which kills moose
Diagram showing the life cycle of Parelaphostrongylus tenuis, passing from the white-tailed deer to members of the moose population

contracting brainworm infection. Brainworm actually results from infection by a nematode parasite, which naturally leeches from the white-tailed deer across eastern and central North America. These deer are able to live with the infection with few to no symptoms.

However, in order for the parasite’s life cycle to be complete, white-tailed deer must be exposed to snails and slugs (gastropods). Areas that are inhabited by white-tailed deer, moose and gastropods can result in P. tenuis disseminating through the moose population.

A correlation has been drawn between logging and the spread of the ghastly brainworm infection. Certain logging practices forced white-tailed deer deep into northern territory, where significant numbers of moose dwell, thereby leading to higher infection rates.

Although not always fatal, brainworm can cause very severe complications, including the following characteristic signs and symptoms:

  • Circling
  • Inability to feel fear
  • Lethargy
  • Rapid eye movement
  • Turning neck and head from side to side
  • Visual issues
  • Weakness in hind limbs

There has been much debate over whether P. tenuis and white-tailed deer populations have been partly to blame for the obvious decline in the moose population. So far, opinion remains divided.

Liver Flukes & Rainfall

Liver flukes (Fascioloides magna) are large flatworm parasites and are, again, found in white-tailed deer.

Liver flukes also form capsules within the livers of cattle, elk, moose, mule deer and sheep; these animals are known as dead-end hosts, since the parasite’s lifecycle is essentially neutered within these hosts.

Liver fluke capsule taken from moose subject
Photograph of a single liver fluke capsule, extracted from the liver of an infected moose

Liver flukes don’t impair white-tailed deer, but do wreak havoc on the integrity of the moose liver, carving their way through the organ and causing extensive fibrosis. Nonetheless,

Life cycle of liver fluke
Diagram showing the life cycle of the liver fluke

fluke worms are not always fatal to the creature, but have been known to cause additional complications. For example, the liver damage can weaken the moose, predisposing it to secondary bacterial infections.

A recent study, performed by Ballard et al., (2006), suggested that fluke worms were a major cause of moose deaths across northwestern Minnesota. In the sample they investigated, the research team concluded that fluke worms were responsible for the highest mortality rate.

They also found that an increase in temperature and rainfall was likely to enhance the reproduction of snails, which carry the unpleasant liver fluke parasite, whilst speeding up the parasite’s life cycle. Simply put, more rainfall equates to more infected snails to pass on infection to moose.

Winter Ticks & Climate Change

Up next is the much maligned winter tick (Dermacentor albipictus), spreading in swathes throughout the moose population of North America, and becoming a recent hindrance to New Hampshire moose.

Winter ticks have been found on many hoofed animals, but seem to preferentially parasitize moose. Large clusters of winter ticks interlock their legs and wait amongst patches of vegetation for an unsuspecting animal to brush past. As a result, a single moose can pick up hundreds of these ticks at any given moment.

According to the Department of Environment and Natural Resources an individual moose can become infested with thousands of winter ticks, which congregate around the back, neck, shoulders, stomach and anus of the animal. Kristine Rines, working for the New Hampshire Fish and Game Department, states that a single moose can become afflicted with as many as 100,000 ticks.

Image showing a number of engorged ticks on a moose
Image showing a number of engorged ticks, peppering the back of a moose

Throughout the year, winter ticks feed on the blood of their victim. By spring, infected moose may transition into what have been dubbed “ghost” moose, a term coined to describe their white appearance after having rubbed away vast patches of skin, in a vain attempt to remove the ticks.

Loss of hair exposes moose to the punishing elements and increases their energy expenditure, as moose spend longer periods grooming. In addition, the ticks’ blood-sucking practices drains them of blood, causing anemia and fatigue.

Tick larvae are most active in the warmer parts of the year, typically during the dry periods of the fall. Lower temperatures adversely impact larvae, and fewer are able to reach their host. Also, when adult ticks fall from their host, during the spring, snowfall makes survival increasingly unlikely.

This has led many researchers to posit that climate change, and an increase in global temperatures, with earlier spring snow melt, to have improved the winter tick’s ability to more effectively complete its life cycle.

Heat Stress

According to the New York Times, climate change could play a contributory factor, aside from enhancing the infective capacity of the previously mentioned parasites. Speaking to the newspaper, Erika Butler, the former wildlife veterinarian at the Minnesota Department of Natural Resources, had this to say:

“It’s complicated because there’s so many pieces of this puzzle that could be impacted by climate change.”

Although the theory is contentious, it is alleged that heat stress can place greater strain on moose. As they are accustomed to living in cold regions, an overall increase in global temperature is alleged to be responsible for the animals having to expend more energy remaining cooler.

In Aug. 2009, a Moose Advisory Committee, launched by the Department of Natural Resources, released a report that indicated climate change was a threat to the moose population within Minnesota.

Ultimately, the decline in the moose population could have a number of other unfortunate consequences. Moose-watching tourism is likely to be affected, whilst other animals within the ecosystem are reliant upon these lumbering creatures to create nesting habitats when grazing.

It seems that the recent moose die-off is associated with a vast number of issues, including brainworm, liver flukes, winter ticks, and factors that researchers are likely unaware of. The issue of whether climate change is affecting their population numbers, however, remains an untested hypothesis.

By: James Fenner


Moose in Minnesota Website

Department of Environmental Conservation

Wildlife Promise Website

Environment News Service

Environment and Natural Resources

The New York Times

OnEarth Article

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