Clinical characteristics of patients with black widow spider bites: A report of 59 patients and single-center experience

Dear editor,

The black widow spider species, also known as the Latrodectus species by its biological nomenclature, is one of more than 40,000 different spider species and one of the most common poisonous species to humans.[1] It is reported to be responsible for most of the clinically significant envenomation among all species of spiders in the USA.[1] There are more than 30 different types of black widow spiders worldwide, and black widow spiders are easily identified by its characteristic shiny black body and strikingly red hourglass-shaped marking on the abdomen.[1] As a kind of world-famous highly toxic arachnid, their venom is highly toxic.[2] Casualties caused by black widow spider bites are reported all over the world in recent years.[3,4] In China, black widow spiders are mainly distributed in Xinjiang Uygur Autonomous Region, and have caused great harm to people’s lives.[5] Clinical characteristics of black widow spider bites are diverse. Except for local symptoms such as swelling, redness, and pain, many patients can develop systemic poisoning symptoms like hypotension, short of breath, and fever, which can lead to organ damage and even death.[6] The severity of poisoning depends on the type and the location of the bites, the level of toxicity, the amount of poison, and the health condition of the bitten individual.[6]

We retrospectively analyzed the clinical data of 59 patients with black widow spider bites in a single center in a ten-year period. We aim to explore the clinical characteristics.

METHODS

Data collection

Medical records of 59 patients with a definite history of black widow spider bites admitted in the emergency department of Xinjiang Bazhou People’s Hospital between May 2008 and September 2018 were retrospectively collected and analyzed. The following clinical information was collected: (1) general information including patients’ name, gender, age, ethnicity, length of hospital stay, and comorbidities; (2) the time of spider bites, the course of the disease, and clinical symptoms and manifestations; (3) laboratory parameters, including white blood cell count, hemoglobin, platelet levels, alanine transaminase (ALT), aspartate transaminase (AST), bilirubin levels, blood urea nitrogen (BUN), creatinine (Cr), and myocardial enzymes (creatine kinase-myocardial band isoenzyme [CK-MB], myoglobin, troponin, lactate dehydrogenase [LDH]); (4) electrocardiograms and imaging examinations, including chest X-rays and computed tomography (CT); (5) treatments; (6) follow-up: hospitalization time with or without sequela.

Statistical analysis

Data with normal distribution were presented as mean±standard deviation (SD). Data with skewed distribution were presented as median (interquartile range). The categorical variables were described as percentages. All analyses were performed using SPSS 22.0 statistical software package (SPSS Inc., USA).

RESULTS

Totally 59 patients were enrolled in this study. The mean age of the entire cohort was 36.9±13.6 years. The ethnic group was dominated by Han nationality, accounting for 93.2% (55/59) of the entire cohort. Forty-three patients were bitten in the field, and sixteen patients were bitten at home. The sites of the bites were mostly located in rural areas or urban-rural junctions. The onset time was mainly between June and September every year, and the peak period was July (accounting for 55.9% of all patients). As to visit time, 12 patients were treated within 4 hours after a bite, 29 patients within 4 to 24 hours, and 18 patients within 25–96 hours. Six patients were transferred from local hospitals. There were 35 patients of limb bites, followed by 16 patients of bites on the trunk, and eight patients of bites on the head and neck.

After the bites, all the patients in our study quickly developed systemic symptoms such as painful expressions, anxious, irritable, restless, and difficulty in breathing. The pain was the characteristic manifestation of black widow spider bites in our study. Totally 42 patients presented with chest and back pain with painful cramps and abdominal muscle stiffness. The local symptoms were evident in bite marks on the wound. After a few minutes after bites, all patients developed a feeling of severe pain in the red and swollen bite site, which was linearly distributed along the blood vessels and rapidly spread to the abdomen and limbs. The area adjacent to the wound site could become painful, erythematous, and edematous. Other symptoms were as follows: nausea and vomiting in 36 (61.0%) patients, abdominal distension in 27 (45.8%) patients, abdominal muscle tension in 59 (100.0%) patients, palpitations in 25 (42.4%) patients, dizziness in 13 (22.0%) patients, headache in 14 (23.7%) patients, chest pain in 33 (55.9%) patients, leg pain in 53 (89.8%) patients, limb weakness in 29 patients (49.2%), hypertension in 7 (11.9%) patients, intestinal obstruction in 19 (32.2%) patients, and heart failure in 5 (8.5%) patients (Table 1).

Table 1.

Clinical characteristics of patients with black widow spider bites

Laboratory findings

Leukocyte elevation was found in 39 patients. The mean white blood cell count was (14.7±7.3)×10⁹/L, and the red blood cells and platelet counts were normal. Thirteen (22.0%) patients had hypokalemia (3.1±0.6 μmol/L), and 28 (47.5%) patients had elevated serum creatine kinase (CK) (665±297 U/L, normal range 0–40 U/L). Serum CK-MB increased to 16.9±3.7 U/L (normal value 0–40 U/L) in 21 (35.6%) patients. LDH increased to 673±271 U/L (normal value 120–250 U/L) in 19 (32.2%) patients. ALT elevated to 297±67 U/L (normal range 0–40 U/L) in 23 (38.9%) patients. Sixteen patients had renal impairment, with serum Cr elevated to 131.9±59.6 μmol/L (normal range 41–86 μmol/L). Twenty-five (42.4%) patients showed sinus tachycardia. Nine (15.3%) patients had premature ventricular beats, and ten (16.9%) patients demonstrated ST-segment depression. Complete or incomplete intestinal obstruction was detected by abdominal CT scan in 17 (28.8%) patients.

Treatment

In the acute phase, strong iodine solutions were used to disinfect wounds. Mild pain was managed with oral analgesics as needed, while moderate and severe pain at the wound site with radiation and characteristic systemic symptoms were treated with opioids and benzodiazepines. Auxiliary treatments included maintaining water and electrolytes balance and correction of acid and base disturbance. We prescribed a small dose of dexamethasone (5 mg twice a day) and 20% calcium gluconate 10 mL for intravenous infusion. Atropine was applied to alleviate the symptoms of nerve damage. Myocardial nutritional therapy was also used, which helped with gastrointestinal decompression for patients with toxic intestinal paralysis. For patients with heart failure, treatments included diuretics, vasodilators, cardiotonics, and anti-arrhythmic agents.

Prognosis

All the patients recovered successfully with no death. The mean hospital stay was 6.1±5.4 days. Two patients had abnormal serum myocardial enzymes at discharge with no other sequela.

DISCUSSION

In recent years, reports of the bite by black widow spiders are increasing in China, and most of the patients are from the Xinjiang Uygur Autonomous Region. The genus Latrodectus derives its ubiquitous nickname “black widow” from its physical characteristics.[1] The black widow spider is well-known for the phenomenon of the female spider devouring the male spider after mating, thereby making her a widow.[1] Symptoms of envenomation range from local irritation and pain to a more systemic syndrome termed “latrodectism” , while latrodectism is characterized by variations in presentations ranging from autonomic disturbance to widespread pain and rigidity.[1] Black widow spider, a medium-sized spider belonging to the genus arachnid, has a body length of 10 to 14 mm and lives in grasslands, deserts, farmlands, stone seams, earth caves, and hay.[2] The patients in this study were all bitten in these places. The time between July and August is its breeding season, and during this period its venom is the most toxic. Black widow spiders would bite when they are disturbed. Therefore, people need to strengthen protection awareness when doing fieldwork during this season.[3] Interestingly, in this study, we found that although Uyghur and Mongolian populations dominated the population of Bazhou and the Han nationality are not dominant, the bitten patients were mostly Han nationality with a percentage of 93.2%, which may be attributed to the Uyghur life experience.

The venom of the black widow spider is an effective weapon for capturing prey and defending against enemies. It is a mixture of various active ingredients containing a protein neurotoxin called α-latrotoxin (α-LTX). At the same time, the receptor of the toxin is a member of G-protein-coupled receptors (GPCRs).[7] Black widow spider toxin is a glycoprotein with a relative molecular mass of 130 kDa, which can act on various synaptic and sodium ion and potassium ion channels. When used as a human synapse, it can cause depolarization of the presynaptic membrane, causing acetylcholine to be released from synaptic vesicles. The massive release of acetylcholine can cause excessive depolarization of the muscles. It causes excessive hyperactivity in autonomic and cerebral cortical neurons, and most patients present with headache, lethargy, irritability, myalgia, tremors, and ataxia.[8] Patients bitten by black widows will quickly develop symptoms of systemic poisoning, including facial pain, anxiety, irritability, difficulty in breathing, restlessness, blurred vision, standing, sputum, chest and back stiffness, and abdominal muscle stiffness. These symptoms of poisoning are closely related to spider toxins.[9] Treatment is mainly based on anti-toxins. Early rehydration can dilute toxins, which can also promote toxin metabolism and prevent shock. Atropine treatment can reduce acetylcholine poisoning. Calcium gluconate (10%) helps relieve muscle pain and cramps. However, calcium gluconate is not recommended anymore. Early application of dexamethasone not only reduces the symptoms of poisoning, but also inhibits allergic stress. Besides, the main components of the venom of the spider are collagenase, protease, phospholipase, hyaluronidase, neurotoxin, and tissue-dissolving toxin. The secreted venom not only damages local tissue of the bite, but also causes local tissue swelling, degeneration, necrosis, ulcer formation, and the binding of neurotoxin to the neuromuscular cell membrane, stimulating the central nervous system, peripheral nerves and autonomic nerves. The main clinical manifestations include limb pain, abdominal pain, bloating, sweating, numbness of the limbs, weakness, chills, and fever.[10] Tissue-dissolved toxin can directly cause tissue necrosis, vasculitis, and systemic reactions.[11] When the toxin interacts with the neurotoxin, it can increase the blockade of cardiac conduction, and degeneration and necrosis of the heart muscle, causing myocardial tissue damage. Symptoms include palpitations, chest tightness, chest pain, and difficulty in breathing. In severe patients, patients may have symptoms of hypotension, heart failure, and even cardiogenic shock.

It is worth noting that many patients can not provide the doctor with a history of poisonous spider bites in the early stage of the disease, so it is easy to have misdiagnosis and diagnosis delays. From the epidemiological characteristics of this study, four patients were admitted to the hospital because of chest pain, accompanied by abnormal electrocardiogram (ECG) and elevated myocardial enzymes. They were diagnosed as myocardial infarction. In addition, eight patients presented with unbearable abdominal distension, and there was a bowel sound in the abdomen, so they were misdiagnosed as intestinal obstruction. Moreover, five patients were diagnosed with soft tissue infections with symptoms such as generalized pain, difficulty in breathing, restlessness, and blurred vision. After asking the medical history again, they were diagnosed accurately. The clinical diagnosis of a black widow spider bite depends mainly on medical history, wounds, non-specific clinical manifestations, and corresponding epidemiological findings.[12] Visualizing the bite along with its associated symptoms and obtaining a detailed history will allow accurate diagnosis.[1] Therefore, patients with a suspected diagnosis should actively collect evidence and confirm the identity of bite spiders.[13-15] To officially confirm the diagnosis, the patient must bring in the spider after witnessing the bite and an entomologist, medical toxicologist, or another qualified specialist must identify the spider.[1] However, this is not necessary, and it is not recommended for patients to capture, harm or handle the spider.[1,16,17] The diagnosis of all patients in our study was repeatedly confirmed by medical history, witness, and wounds to avoid misdiagnosis.[18]

In order to facilitate diagnosis, we divide the disease of poisonous black widow spider bites into three types based on clinical symptoms and literature reports. (1) Nervous system poisoning type. There were 52 (88.1%) patients in this group; symptoms include pain, weakness, dizziness, and headache. (2) Toxic myocarditis type. There were 35 (59.3%) patients in this group, and five patients presented with heart failure; symptoms include palpitations, chest tightness, chest pain, hypotension with markedly elevated myocardial enzymes, and abnormal electrocardiogram. (3) Intestinal paralysis type. There were 39 (66.1%) patients in this group, and 17 (28.8%) patients developed signs of intestinal obstruction; symptoms include persistent abdominal pain with nausea, vomiting, abdominal muscle tension, and liver damage.

CONCLUSIONS

Mild symptoms of black widow spider envenomation include pain and skin irritation. Severe symptoms, also known as “latrodectism”, consist of systemic toxicity with diffuse pain, muscle spasm, and autonomic dysfunction. Laboratory findings include elevation of white blood cell count and myocardial enzymes, impairment of hepatic and renal function. The spider venom is a powerful poisonous neurotoxin. Treatment is usually symptomatic with a combination of opioid analgesics, muscle relaxants, and auxilliary treatments. Most patients have a good prognosis without sequela. Enhanced awareness and familiarity with epidemiological and clinical characteristics of black widow spider bites could reduce misdiagnosis.