By Dr. Denise Crumbaker, DVM
Black widow spiders have long been known as a cause of venomous spider bites in people, but they also can inflict very severe disease on multiple companion animal species. Black widows can be found in every state within the US with the exception of Alaska and Hawaii. They typically prefer to live in dimly lit areas such as woodpiles or corners. The web has a characteristic funnel shape and tends to appear somewhat irregular. Black widows are around an inch in length. Color varies from brown, red, to shiny black. Female black widows are identified via the red or orange hourglass shape on their black abdomen. Immature females can have a red or beige color pattern on their abdomen which tends to change to black as the spider ages, but they are still capable of causing severe envenomation with a bite. Male black widow spiders do not have fangs that can penetrate mammalian skin.
Black widows control the amount of venom they inject into a victim. It is estimated that approximately 15% of human bites are “dry bites,” meaning no venom was injected. In companion animal species, cats, guinea pigs, and horses are extremely sensitive to the effects of the venom. Dogs can also show severe clinical signs after a bite, but are considered more resistant to the venom than cats. The venom contains proteins that primarily affect the nervous system by resulting in destruction of nerve endings and subsequent paralysis of the victim.
Signs of black widow envenomation typically start within around 8 hours after the bite. Diagnosis can be difficult as often times the puncture wounds cannot be seen. Cats will sometimes eat and then vomit up the spider. Symptoms include muscle cramping and progressive pain, tremors, and restlessness. Pain can become very severe. Swelling of the face can also be seen. There does not tend to be significant swelling around the bite site, but the area tends to be painful to the touch. In many patients heart rate and blood pressure can become dangerously elevated. As time passes, paralysis becomes evident and patients can go into respiratory and/or cardiac failure.
The primary treatment of black widow spider bites is the administration of antivenin. The antivenin is specifically designed to counteract the toxins in the venom and thus prevent progression of the syndrome. Administration of antivenin tends to start providing relief within 30 minutes of administration. Additional treatments can include muscle relaxants, pain medications, and IV fluids. Patients that are showing signs of respiratory muscle paralysis and are having difficulty breathing may require significant support during the course of treatment.
The overall patient prognosis can remain very uncertain for several days after the bite, especially in cats. In humans, the average duration of the bite syndrome is 3 to 6 days. Complete recovery can take weeks and muscle pain, weakness, and general malaise can persist during this time.
AMVS is a 24-hour veterinary facility providing specialty internal medicine, surgery, emergency and critical care, physical rehabilitation, pain management, and blood bank services for pets. They are located in Longmont at 104 S. Main St. For more information, go to www.AspenMeadowVet.com.