Skunk spray toxicosis: An odiferous tale

Most people have no problem identifying a North American skunk by sight or smell. Skunks are of the order Carnivora, family Mephitidae. The six species that exist in North America are the striped skunk (Mephitis mephitis), the Western spotted skunk (Spilogale gracilis), the Eastern spotted skunk (Spilogale putorious), two species of hog-nosed skunk (Conepatus mesoleucus and Conepatus leukonutus), and the hooded skunk (Mephitis macroura). Skunks are primarily crepuscular—most active during twilight, dawn, and dusk. Skunks have excellent hearing and sense of smell but do not see well.1

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A SKUNK'S LINE OF DEFENSE

Skunks are docile but will defend themselves when threatened. A skunk's first line of defense is defensive posturing. A skunk will hiss, stamp its feet, and raise its tail as a warning. If the warnings are ignored, a skunk will spray anal gland secretions (referred to as either spray or musk).

Skunks have two anal glands, one on each side of the anus. The anal gland secretions contain a mixture of sulfur-containing thiols. The odor—which has been described as similar to that of a combination of rotten eggs, garlic, and burnt rubber—tends to drive away most predators.2 Skunks can spray these secretions 7 to 15 ft (2 to 5 meters) and are highly accurate in their aim. Getting sprayed by a skunk is commonly called being skunked. Skunk spray has been used as a biological weapon.2

The skunk's anal gland secretions contain seven major volatile components: three major thiols, three major thioacetates, and a methylquinoline. These are divided into thiols and acetate derivatives of the thiols. Two of these thiols, (E)-2-butene-1-thiol and 3-methyl-1-butanethiol, are responsible for the repellent odor. These two thiols constitute 51% to 70% of the anal gland secretions.

The thioacetates are not as initially odiferous on contact but are converted to more potent thiols with the addition of water. This chemical reaction may explain why some animals continue to smell skunky after a bath—thioacetates trapped in fur continue to release thiols under damp conditions.

The seventh component is an alkaloid 2-methylquinoline, which is not as volatile as the thiols and has a nitrogenous base. The chemical composition and percentages of the volatile components may vary among skunk species. Numerous minor components differ among individual skunks and species.3,4

EFFECTS OF SKUNK SPRAY

Although pet owners seldom witness their pets being sprayed by a skunk, the odor is immediate and unmistakable when spraying occurs. Ocular edema, conjunctivitis, drooling, and squinting are commonly noted in animals that have been sprayed. Many dogs will rub their faces, roll, sneeze, and vomit. Temporary blindness may occur.

Exposure to skunk spray can be oral, dermal, ocular, and respiratory. Dermal absorption of the spray is minimal. The severity of signs may depend on a pet's proximity to a skunk when being sprayed and the area of exposure (face vs. legs or side). If an animal is sprayed directly in the face, inhalation can occur.

In rare instances, Heinz body anemia, methemoglobinemia, and hemoglobinuria may occur a few hours to 24 hours after exposure (ASPCA Animal Poison Control Center Antox: Unpublished data, 2011).5 In these cases, the thiols in the skunk spray cause oxidative damage to hemoglobin. The thiols react with oxyhemoglobin in an oxidation-reduction reaction. This reaction forms methemoglobinemia, thiyl radicals, and hydrogen peroxide. Thiyl radicals and hydrogen peroxide are highly reactive and combine with hemoglobin sulfhydryl groups, resulting in Heinz bodies and subsequent hemolysis. (Other substances that cause oxidative damage to red blood cells include onions, garlic, acetaminophen, benzocaine and other local anesthetics, naphthalene moth balls, and zinc.5)

Although there are no reports of a cat developing methemoglobinemia from skunk spray, feline red blood cells are more sensitive to oxidative damage than are the red blood cells of other species. Cats have eight free sulfhydryl groups on their hemoglobin (versus four in dogs), which results in increased susceptibility to oxidative damage.6,7 Japanese breeds of dogs (Tosa, Shiba Inu, and Akita) are more susceptible to oxidative damage to red blood cells compared with other breeds of dogs.8

CASES OF SKUNK SPRAY TOXICOSIS

The ASPCA Animal Poison Control Center's toxicology database from November 2001 to May 2011 included cases of 107 patients (102 dogs and five cats) that were exposed to skunk spray and that developed clinical signs. Only those signs assessed as having either medium or high likelihood of resulting from the skunk spray were included. Most dogs had mild clinical signs. Clinical signs reported in the cats included odor, conjunctivitis, and squinting.

A search of the literature revealed only one report of Heinz body anemia in a dog after exposure to skunk spray.5 Two cases were identified in the ASPCA toxicology database. One involved a 2-year-old 34.5-lb (15.63-kg) neutered male Pharaoh hound that was sprayed heavily in the face. Initial Heinz bodies were noted three to four hours after exposure and continued to worsen during the subsequent 12 hours. The dog developed mild to moderate Heinz body anemia but recovered with symptomatic and supportive care. The dog was released to the owner the next day.

A second case involved a 5-year-old 38.6-lb (17.5-kg) intact male boxer. The dog had a history of being sprayed by a skunk five times before, although it is unknown how close together the incidences occurred. The dog escaped from the house and when the owner found the dog the next morning, the dog smelled strongly of skunk spray and was tremoring. The dog was brought to an emergency clinic more than 12 hours later. Nearly 100% of the red blood cells studied contained Heinz bodies. Results of laboratory testing confirmed methemoglobinemia. The dog had a seizure and died. The owner requested cremation and did not authorize the release of histopathologic and other diagnostic findings. To our knowledge, this is the only death related to a skunk spray in a dog (ASPCA Animal Poison Control Center Antox: Unpublished data, 2011).

TREATMENT

Treatment of skunk spray is primarily symptomatic and supportive. Dermal decontamination involves bathing. The goal is to convert thiols into nonodorous compounds. Thiols are not water-soluble, even with soap. A baking soda and peroxide mixture will oxidize thiols into water-soluble sulfonates (see "Krebaum skunk odor removal formula" below for recipe and instructions). Pets should be bathed outside so the spray does not contaminate household furnishings.4

For ocular exposures, flush the animal's eyes with tepid water. If an animal has received a heavy spray or multiple exposures, obtain baseline blood work. A complete blood count and serum chemistry profile should be obtained on arrival at the clinic. Monitor the animal for the next 72 hours.

If clinical signs consistent with methemoglobinemia or Heinz body anemia develop, administer intravenous fluids. Blood transfusions may be required. To treat methemoglobinemia, give N-acetylcysteine at a 140-mg/kg loading dose followed by 70 mg/kg orally or intravenously every six hours for six to eight treatments.

Skunks can carry rabies. If a pet is bitten by a skunk, initiate appropriate treatment, prophylaxis, and monitoring, and report the case to the proper authorities.

Charlotte Means, DVM, MLIS, DABVT, DABT

ASPCA Animal Poison Control Center

1717 S. Philo Road, Suite 36

Urbana, IL 61802

REFERENCES

1. Skunk (Mepitidae) in depth. Available at: http://eduscapes.com/nature/skunk/index1.htm. Accessed June 10, 2011.

2. Wikipedia contributors. "Skunk," In Wikipedia, The Free Encyclopedia website. http://en.wikipedia.org/wiki/Skunk Accessed June 10, 2011.

3. Wood WF. The history of skunk defensive secretion research. Chem Educator 1999;4(2):44-50.

4. Wood WF. Chemistry of skunk spray. 1998. Updated on 6 October 1998. Available from: http://users.humboldt.edu/wfwood/chemofskunkspray.html. Accessed on June 10, 2011.

5. Zaks KL, Tan EO, Thrall MA. Heinz body anemia in a dog that had been sprayed with skunk musk. J Am Vet Med Assoc 2005;226(9):1516-1518, 1500.

6. Robertson JE, Christopher MM, Rogers QR. Heinz body formation in cats fed baby food containing onion powder. J Am Vet Med Assoc 1998;212(8):1260-1266.

7. Fettman MJ. Comparative aspects of glutathione metabolism affecting individual susceptibility of oxidative damage. Compend Contin Educ Pract Vet 1991;13(7):1079-1088.

8. Yamoto O, Maede Y. Susceptibility to onion-induced hemolysis in dogs with hereditary high erythrocyte reduced glutathione and potassium concentrations. Am J Vet Res 1992;53(1):134-137.

Krebaum skunk odor removal formula*

• 1 quart fresh 3% hydrogen peroxide

• ¼ cup baking soda (sodium bicarbonate)

• 1-2 tsp of liquid dishwashing detergent

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For large dogs, add one quart of tepid water to ensure complete coverage.

Mix the above ingredients together.

Bathe the animal outdoors. Apply the formula to the pet, working deeply into the fur, and allow it to set for five minutes.

Rinse with copious amount of water after five minutes.

Repeat if necessary.

Hints

• The mixture must be used promptly and will not work if stored for any length of time.

• Do not store in a closed container. The container could break as the peroxide releases oxygen.

• The pet's fur (as well as clothing, towels, and carpeting) may be bleached by the formula.

*Source: Krebaum P. Skunk odor removal. Chem Engineer News 1993;Oct 18:99.