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Black Widow Spider Venom Toxicosis in Cats

The black widow spider belongs to the genus Latrodectus – the widow spiders. In the U.S., the three significant species to watch for are the Western widow, the Northern widow, and the Southern widow spiders, all of which are highly venomous to domestic pets and humans. The Western widow is found in western regions of the United Sates; the Northern widow is found in the northernmost U.S. and southeast Canada; and the Southern widow is found in the southeast U.S., from Florida to NewYork and into many of the southwest states. They are found in every state except Alaska and are often found residing around buildings and human habitations. 

The females measure about 2–2.5 cm in length and are the larger of the genders. She is shiny black with a red or red-orange hourglass shaped mark on the underside of her abdomen, and in some females, there is also a patch of red on the top of the abdomen, above the spinnerets. The immature female is more of a brown color with red to orange or yellow stripes across the top abdomen that change into the hourglass shape as she ages and darkens to black. The male is significantly smaller, about half the size, with light brown coloring, and lacking the red hourglass marking the female is recognized for. The male is not regarded as a threat, as it is typically the female that bites.

Bites may be dry, with no venom injected. The venom is a potent neurotoxin, opening channels at the presynaptic nerve terminal and causing massive release of acetylcholine and norepinephrine, both of which can cause sustained muscular spasms and paralysis. A cat may be bitten while indoors or outdoors, as black widows are known to frequent both. No one cat is more at risk than another, but young and old cats are at an increased risk for complications due to their weaker immune systems.

Symptoms and Types

• Early, marked paralysis
• Abdominal rigidity
• Severe muscle pain in the back, chest and abdomen, manifested by howling and loud vocalizations
• Muscle tremors and cramping
• Trouble breathing, respiratory collapse due to abdominal muscle paralysis
• Increased blood pressure and heart rate
• Incoordination and inability to stand (ataxia)
• Excessive salivation and restlessness
• Vomiting - not unusual for a cat to vomit up the actual spider
• Diarrhea
• Death, if anti-venom treatment is not given quickly

Causes

• Very young or old animals are at increased risk of severe reactions because of weaker immune systems
• Animals with systemic high blood pressure are at increased risk for a fatal outcome

Diagnosis

This disease is difficult to diagnose because the symptoms may be caused by other diseases. complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis, as well as a thorough physical exam of your cat. Your doctor may also want to test a sample of your cat's stool. If possible, take a sample of your cat's stool and/or vomit with you to the veterinary clinic, this can help your doctor to make the diagnosis that much faster. Your veterinarian will be looking for wounds to the skin, at which point a bite mark may be found. Muscle rigidity and abdominal rigidity are classic signs of black widow envenomation.