Lightning Strike and Electrical Injury in Animals

Electrical injury due to lightning strike is seasonal, tends to be geographically restricted, and is supported by meteorological events. Although large animals are the predominant species affected by lightning strikes, small animals can be exposed, especially during shared outdoor activities with humans.

Dogs appear to be more susceptible to lightning injury than humans are. Small dogs are thought to be less susceptible than large dogs. In cattle, adults are more likely than calves to experience lightning strike.One hypothesis to explain the higher susceptibility of quadrupeds compared to humans is that, in quadrupeds, the electrical current passes through the heart when travelling through points of ground contact between forelimbs or between forelimb and hindlimb, whereas in standing humans, the heart is remote from the current's path between the feet.

An explanation for the difference in lightning injury susceptibility between animals of different sizes is that larger animals have greater potential differences of electrical charge between their front feet and hindfeet than smaller animals have, related to their proximity to the electrical source. These greater potential differences in larger animals increase the current conducted through the body and increase the risk to the animal.

Lightning injuries occur by the following six mechanisms, in decreasing order of frequency:

• step potential (ground current)

• side flash (partial current from proximity to main nearby strike)

• upward streamer (upward charge induced from the ground)

• direct strike

• touch potential (contact with struck object)

• blast (barotrauma from superheated and then cooled air)

Lightning strikes vary in intensity and in the objects struck in the vicinity of the affected animals. Step potential is the most common mechanism of lightning injury and occurs when the current is propagated on and in the ground away from the lightning strike.

Certain types of trees, especially hardwoods such as oaks and those that are tall and have spreading root systems just beneath the ground surface, tend to be struck by lightning more often than others. Electrification of these root systems charges a wide surface area, particularly when the ground is already damp. When roots beneath a shallow pool of water become charged, the pool becomes electrified.

The conductivity of soil varies by type: loam, sand, clay, marble, and chalk are good conductors (in decreasing order); rocky soil is not. These characteristics, along with the location of animals, largely influence whether injuries are external or internal.

All of these factors together determine whether a definitive or circumstantial diagnosis for lightning strike as the cause of injury to animals can be made.

In small animals, chewing of electrical cords is the most common cause of electrical injury. Affected animals tend to be young (< 2 years old) because they are more likely to chew on cords. There might be a seasonal pattern of injury related to the use of decorative lights during holiday seasons.

Accidental electrical injury of farm animals in a barn or adjacent confinement pen usually is due to faulty wiring. A tile drain can spread an electrical charge throughout its course. Downed or sagging transmission wires or damaged electrical wires can electrify a pool of water or water source, fence, or building; and an animal can make contact with electrified water or also directly contact such wires.

Sublethal electrification of a water or milk line stanchion or a metal creep or guardrail can result in widespread distribution of electrical current throughout the stable that can lead to signs of water deprivation in or feed refusal by affected animals.

The extent of electric shock varies. In most instances of electrocution by lightning, death is instantaneous, and the animal falls without a struggle. For other types of electrical injury, survivability depends on the electrical source and on the individual and particular environmental circumstances. 

Death from electric shock usually results from cardiac or respiratory arrest. Passage of current through the heart generally produces ventricular fibrillation, and neurological injury from direct CNS involvement can affect the respiratory center or other vital nuclei in the brain or brainstem.

Occasionally, an animal that has received an electric shock becomes unconscious but recovers in a few minutes to several hours. Residual neurological signs (eg, depression, paraplegia, cutaneous hyperesthesia, blindness) can persist for days or weeks or be permanent.

During electrical contact, respiratory arrest can result from tetanic contractions of the respiratory muscles. If the animal survives the electrical contact, respiratory distress can be caused from facial or nasopharyngeal edema and neurogenic pulmonary edema.

Surface burns, ranging from first-degree through fourth-degree burns, might be noted at the point of contact with the electrical source (see tongue and palate electrical injury images). For animals that have chewed on electrical cords, dental fractures and oronasal fistulas are also possible.

Electrical injury, tongue, cat

Image

Courtesy of Dentistry and Oral Surgery Service, UC Davis.

Electrical injury, palate, cat

Image

Courtesy of Dentistry and Oral Surgery Service, UC Davis.

Smaller animals, such as pigs, that contact electrified water bowls, creeps, or fencing can be killed instantly or thrown some distance by the strength of the shock. Electrocuted pigs are often recumbent and can have sustained spinal, pelvic, or limb fractures resulting from severe muscular contractions.

• Circumstantial evidence (eg, carcass location, absence of other disease processes)

• Internal or external histopathological or gross evidence of injury

• CBC and serum biochemical panel

• Radiography

The diagnosis of lightning strike or electrocution is almost always facilitated by circumstantial evidence—ie, location of the carcass(es) and absence of other disease processes when animals are examined at necropsy. The magnitude, duration, and direction of the current, flash, or blast produce varying degrees of internal or external histopathological or gross evidence of injury. In animals that survive, CBC and serum biochemistry results are typically unremarkable; however, hyperkalemia, rhabdomyolysis, and hemolysis can occur secondary to tissue hypoxia and necrosis. Radiographic findings of noncardiogenic pulmonary edema might support the diagnosis in small animals.

Classic gross lesions of injury from lightning strike or electrocution are not consistently observed, because of the multiple individual, technical, and environmental variables associated with electrical and lightning injuries. Circumstantial evidence, careful investigation of the affected animal(s) and environment, and elimination of other causes for unexpected or multiple animal deaths often form the basis of a diagnosis.

The likelihood of external burn lesions or damage is higher in cases of direct electrical contact and in lightning injuries characterized by direct strike, touch potential, side flashes, or blast mechanisms of injury. Injury produced by step potential (ground current) or by current passed through electrified earth is less likely to involve specific lesions. Singe marks are rarely found on recovered animals.

Keraunographic markings (branchlike erythematous markings or patterns on skin after a lighting strike) are considered pathognomic of lightning injury in humans; however, they are rarely described in animals, presumably because they are obscured by pigmentation and hair. These markings also fade and disappear within 1–2 days. Keraunographic markings of the ground can also be observed near animals struck by lightning.

Few conditions affecting livestock cause such peracute death of multiple animals clustered in a small area as lightning strike does. Rigor mortis develops and passes quickly. Postmortem distention of the rumen occurs rapidly and must be differentiated from antemortem ruminal tympany; however, the lungs are not compressed as in bloat.

Probably the best indication of instantaneous death due to lightning strike or electrocution is the presence of hay or other feed in the animal’s mouth. Supportive evidence includes presence of normal ingesta (especially in the stomach or rumen), lack of frothy ingesta (frothy bloat), and presence of normal feces in the lower GI tract and occasionally on the ground behind the animal.

Nonspecific pathological findings of electrocution include organ congestion and petechiation, particularly within the upper respiratory tract. If lightning struck the ground nearby, close examination of an affected animal's feet might provide the only physical evidence of pathology. The coronary bands and soles should be closely examined because those areas have lower electrical resistance compared to the hoof capsule and might be more likely to show signs of injury.

Often, cadavers from lightning strike or electrocution are not immediately found, and postmortem autolysis might prevent a meaningful necropsy. Therefore, the presence of dead animals under a tree, hanging through or near a wire fence (see electrocuted cattle image), or clustered around a light pole is strong evidence of electrocution by lightning strike even in the absence of physical evidence or any grossly visible lesions on the cadaver.

Electrocution, cattle

Image

Courtesy of Dr. Roy Lewis, Westlock Veterinary Clinic.

Farm animals often are insured against lightning strike, and the insurance claims agent or veterinarian asked to sign an insurance form should closely examine the situation that prompted the claim. The investigator should ascertain that the animal actually died in the high-risk location and was not moved there after death, as might occur during cleanup or deliberate tampering with the investigation.

Similarly, examination of recent weather reports confirming thunderstorms, if available, is an important part of the process to substantiate an insurance claim. A well-documented description of where the animal(s) died and the results of a necropsy examination are usually acceptable to support an insurance claim of lightning strike.

• Supportive care

• Tracheostomy, if indicated

• Cardiac, neurological, and GI medications, as needed

• Euthanasia

Animals that survive a lightning strike benefit from or require supportive care. Euthanasia is warranted for animals that are recumbent with fractures, irreversible neurological injury, or severe muscle injuries.

Treatment of lightning strike injury and electrical injury depends on the clinical signs observed. Animals in cardiovascular shock require fluid resuscitation; however, fluids should be administered judiciously because of the potential for cardiogenic shock and neurogenic pulmonary edema. 

Treatment of respiratory distress should be based on the mechanism of injury: tracheostomy, if there is airway obstruction from oropharyngeal edema; supplemental oxygen, if neurogenic pulmonary edema is the cause.

Burns should be managed with local wound therapy. Pain management is necessary for burns and for muscle soreness from tetanic muscular contractions induced by electric shock. Other derangements (cardiac arrhythmias, seizures, ileus, etc), if present, are treated with appropriate medications.

The prognosis for animals that survive an initial electric shock appears to be good, provided that clinical signs are reversible and that recumbency, if present, is not caused from fractures, muscle injuries, or neurological injury.

• Mann FA. Electrical and lightning injuries. In: Drobatz KJ, Hopper K, Rozanski E, Silverstein DC. eds. Textbook of Small Animal Emergency Medicine. John Wiley & Sons; 2018:956-961.

• Schulze C, Peters M, Baumgärtner W, Wohlsein P. Electrical injuries in animals: causes, pathogenesis, and morphological findings. Vet Pathol. 2016;53(5):1018-1029.

• Also see pet owner content regarding lightning strike and electrocution.