Along came a spider…

As the weather warms up in Washington, indoor and outdoor spiders seem to materialize overnight to decorate every inch of our yards and every nook and cranny in our homes. While this may be unnerving for some, there’s usually nothing to fear — almost all of the 950+ spider species in Washington are not harmful to people. Our state is home to one infamous spider with “medical importance,” though: the black widow.

Black Widow spiders are mainly found in Eastern Washington, with a few small populations in Western Washington. These spiders are not aggressive — bites typically occur when the spider is accidentally disturbed, trapped, or crushed. Examples include moving materials in the garage, cleaning up yard debris, or putting on gloves or boots. Accordingly, envenomations most commonly occur from April to October, when people are working in their yards and preparing spaces for summer or fall.

The venom of the black widow spider contains a neurotoxin called alpha-latrotoxin, which triggers a release of neurotransmitters including acetylcholine, norepinephrine, dopamine, glutamate, and y-neuropeptides. Symptoms can range from mild to severe, including local and systemic effects. Most of the systemic effects patients experience are due to the massive release of neurotransmitters.

Diagnosing a black widow spider bite

The only way to definitively diagnosis a black widow spider bite is if the patient actually sees and correctly identifies the spider, and/or they bring in the spider for identification. Oftentimes, clinicians must instead rely on circumstantial cues and clinical effects to diagnose.

First, consider the environmental cues around the bite. Black widow spiders usually live in secluded, dark habitats, such as garages, sheds and outbuildings, woodpiles, hay bales, outdoor furniture, and infrequently used tools or equipment. It is rare to find a black widow spider in indoor living spaces.

Female black widow spiders are more distinctly identifiable than males, and are also more likely to have a significant bite (males typically have less venom and weaker biting muscles). Adult females are approximately one half-inch long, shiny black, with a red or yellow-orange mark on their abdomen. The mark may resemble an hourglass, triangles, or one to two dots.

Clinical Presentation

The bite, if noticed, is usually described as an initial pinprick sensation. The bite mark may have a small puncture wound with redness and localized diaphoresis. The bite site may also present as a “target:” a blanched patched surrounded by a red ring. Sometimes the bite site can be subtle and may go unnoticed.

Some patients do not have progression of symptoms. Those that do will develop symptoms within the first few hours. The most commonly described symptoms are myalgias and muscle cramping. In moderate to severe envenomation, pain can extend from the bite site contiguously to the abdomen or chest. Three to four hours after the bite, the patient may experience muscle cramping and fasciculations, paresthesias, tachycardia, hypertension, nausea, and vomiting. The abdominal cramping and rigidity can be severe enough to mimic an acute surgical process. Some patients additionally report a neurological effect described as a “feeling of impending doom.”

An additional clinical phenomenon known as ‘‘Latrodectus facies’’ or ‘‘facies latrodectismica’’ has occasionally been described following envenomation. This phenomenon is characterized by development of periorbital edema, lacrimation, and blepharospasm as well as occasional facial grimacing.

Differential Diagnosis

The final step in diagnosing a black widow spider bite is considering a differential diagnosis. The muscle spasms, pain, and other systemic symptoms from a bite can mimic several other conditions, including surgical abdomen (i.e., acute appendicitis), myocardial ischemia or infarction, rabies, and tetanus.

Diagnostic Testing

Laboratory data generally are not helpful in management or predicting outcome. Currently, there is no clinically available test to confirm black widow spider envenomation.

Treating a black widow spider bite

First and foremost, clean the bite site and ensure the patient is up to date on their tetanus immunization.

The routine use of antibiotics is not recommended.

The remainder of treatment is focused on supportive care and pain relief. Less severe pain can be treated with acetaminophen; opioids may be used for severe pain. For muscle spasms, utilize muscle relaxants or benzodiazepines. Calcium is no longer recommended as an effective treatment. Most symptoms will resolve within a few days.

Closely monitor high risk patients: young children and older adults, patients with a history of or a current cardiac condition, and people who are pregnant.

The morbidity of latrodectism is high, with pain, cramping, and autonomic disturbances, but mortality is low. An effective antivenom derived from horse serum is available for serious systemic symptoms in high risk patients or patients with severe refractory symptoms. The current Black Widow Antivenom was FDA approved in 1936. Clinical experience with the antivenom has demonstrated its safety, but, there have been rare reports of serious hypersensitivity reactions.

Sources:

• UpToDate: Clinical manifestations and diagnosis of widow spider bites
• POISINDEX Managements: Spider-Latrodectus Species
• Washington State Department of Health: Spiders