Insect Bites on Dogs: Signs, Symptoms and Treatment

Bees, Wasps and Ants

Unfortunately, insect stings are a common problem faced by pet owners. Most medically important insects that sting consist of three groups: Vespidae (wasps, hornets, and yellow jackets), Formicidae (i.e. fire ants), and Apidae (i.e. honeybees, African killer bees). Vespidae (wasps, hornets, yellow jackets) tend to be more aggressive than Apids (honeybees). Vespids are capable of stinging a victim multiple times since their stinger is not barbed and is not lost in the victim. In contrast, Apids have a barbed stinger that remains in the victim. The bee dies shortly after the stinging apparatus is pulled from its body. The stinger can still pump venom into the victim even when it is detached from the body of the bee.

Honeybees typically only sting when aggravated. African killer bees travel in swarms and become aggressive if provoked. Most dogs and cats are exposed to stings when they disturb a nest or swarm. Oftentimes they are stung in the face, nose, mouth, or feet, but if they disturb a hive, they can be stung anywhere on their body!

An estimated lethal dose in mammals is 20 stings/kg (1 kg= 2.2 lbs). However, a single sting can be deadly in sensitive individuals. Multiple stings by hornets and wasps are more likely to result in serious complications.

Clinical signs can vary:

• Localized (mild to severe) pain at the site of the sting, swelling, and edema may occur within seconds. This can be self-limiting (no treatment needed). This accounts for the majority of stings.
• A puncture wound or an imbedded stinger may be noted.
• The surrounding area may be erythematous (red), swollen, and hot. 
• The patient may be pruritic (itchy). Wheals (hives) may be present.
• Patients with anaphylaxis (which can occur within 10 minutes) may exhibit vomiting, diarrhea, weakness, collapse, seizures, respiratory distress, and cardiovascular arrest.
• Cats may exhibit vocalization, hypersalivation, ataxia, and pruritus (itchiness).
• Other clinical signs may occur if secondary complications arise from anaphylaxis or delayed-type hypersensitivity reactions.

• No specific antidote exists. Most envenomations resolve without major intervention but some patients may experience severe abnormalities.
• Any embedded bee stinger should be removed, preferably with a credit card or stiff object, being careful not to further compress the venom sac.
• Cold compresses like an ice pack or a bag of frozen peas applied to the sting site may help to alleviate pain and swelling.
• Topical application of a thick paste made of baking soda and water can be soothing, as well as an oatmeal bath.
• In the case of bee or wasp stings, aloe vera gel can be applied to help sooth the pain and burning sensation due to the sting or bite.
• Hydrocortisone cream applied topically may help provide relief.
• Administration of diphenhydramine (Benadryl) can be beneficial, but check with your veterinarian first on use and dosage.
• Analgesic therapy may be needed in some cases (check with your veterinarian).
• Patients with anaphylaxis require more intensive therapy and nursing care.

Monitoring:

• For patients with mild clinical signs, home observation for 12-24 hours is often sufficient. The owner should return the pet to the hospital if clinical signs do not resolve within 24 hours or new signs develop.
• Patients with anaphylactic reactions require hospitalization and intensive monitoring. Some adverse effects may not be noted until 3-14 days after the sting.
• Prognosis is good for localized reactions, as most clinical signs resolve within 12-24 hours with appropriate therapy. Prognosis is fair to good for patients with more severe reactions, providing prompt medical care is provided.
• Patients that experience significant complications have a poorer prognosis but recovery is still possible. Death can occur from severe anaphylaxis or delayed-type hypersensitivity reactions.
• Patients that experience a large number of stings are more at risk for serious clinical signs.  However, some individuals that are hypersensitive may exhibit severe clinical signs with just one sting.

Prevention:

• Avoidance is the main form of prevention. Animals should be kept away from hives and ant colonies.
• Consider having preloaded syringes of epinephrine or an Epipen® at home for animals that have a history of prior anaphylactic or severe reactions to stings.
• OFF DEET wipes can be used as a repellent.  For smaller dogs, children’s DEET may be better as its less concentrated.  It can be wiped lightly on the dog’s body and is safe.

Spiders

Envenomation and systemic poisoning from spider bites are possible. More than 30,000 species of spiders have been identified worldwide and most spiders are venomous. However, most spiders cannot produce serious bites because of their tiny fangs and small mouth parts. The most medically important groups of biting spiders are the widow spiders and the recluse spiders.

Female black widows are up to 20 times larger than males, and they are more venomous than males. Females are dark grey to black and have a characteristic red or orange hourglass marking on their globous abdomen. Immature females are red, brown, or beige and do not have the characteristic hourglass marking. Immature females can also produce severe envenomation. Black widow spiders prefer dark, draft-less, dry areas. Most black widow bites in people occur during colder months when spiders move inside.

Black widow spiders produce one of the most potent venoms by volume. It is 100 times more potent than pit viper venom on a volume-to-volume basis. Single bites from black widow spiders can be lethal to small animals. Some animals are more susceptible to black widow envenomation than others. Guinea pigs, horses, and cats are highly susceptible but dogs are relatively resistant to the effects of the venom.

Clinical signs develop typically within 8 hours of envenomation. The initial bite can be moderately painful, which contrasts with the relatively painless bite of the brown recluse spider. No local tissue changes typically surround the bite except for mild erythema, which is another contrast to the skin necrosis of the brown recluse spider bite.

Clinical signs occur shortly after the bite of the widow spider (i.e. within 8 hours): 

• Muscle pain, cramping, muscle fasciculations, abdominal rigidity without tenderness,
• vomiting, diarrhea
• restlessness, vocalization
• hypersalivation (excessive drooling)
• seizures
• hypertension, tachycardia (fast heart rate)
• ataxia (wobbliness), flaccid paralysis and respiratory distress.
• Bites can be fatal. Death is more common in cats than dogs.

Therapy

• Positive identification of the spider is ideal
• The most effective therapy for black widow envenomation is administration of antivenin. The antivenin works quickly and clinical signs usually resolve within 30 minutes. 
• Antihistamines are used to prevent reactions to the antivenin. 
• Medication is also used for pain management. 
• Local wound therapy is undertaken if the spider bite site is found.
• Blood pressure monitoring is recommended, especially in patients on fluid therapy.

Many dogs do not require medical treatment. Overall prognosis for black widow spider bites is good in dogs. They are more resistant to the effects of widow spider venom than cats. Correct diagnosis and treatment is essential for a favorable outcome. Therapy with antivenin typically provides the quickest resolution but complete recovery can take several weeks in some cases.

References:

1. Mazzafero EM: Spider Bites Brown Spiders. Blackwell Five Minute Veterinary Consult and Clinical Companion Small Animal Emergency and Critica 2010 pp. 767-773.
2. Hopper K: Spider Bites: Fear and Loathing in Las Vegas. Western Veterinary Conference 2006.
3. Mazzafero EM: Spider Bites Black Widow. Blackwell Five Minute Veterinary Consult and Clinical Companion Small Animal Emergency and Critica Ames, Wiley-Blackwell 2010 pp. 761-766.
4. Peterson ME: Black widow spider envenomation. Clin Tech Small Anim Pract 2006 Vol 21 (4) pp. 187-90.
5. Peterson ME: Venomous Arthropods. Western Veterinary Conference 2007.
6. Twedt DC, Cuddon PA, Horn TW: Black widow spider envenomation in a cat. J Vet Intern Med 1999 Vol 13 (6) pp. 613-6.
7. Poppenga RH: Zootoxins. Western Veterinary Conference 2002.
8. Brutlag A: Snakes, Spiders and Scorpions, Oh My! Or, Managing Envenomations. Western Veterinary Conference 2010.   
9. Hackett T: Spiders and Snakes: Recognizing and Treating Envenomations. Atlantic Coast Veterinary Conference 2007.
10. Atkins LB: Spiders and Snakes--Envenomation. International Veterinary Emergency and Critical Care Symposium 2006