Allergy to spider venom. Does it happen?

There is a belief that European spiders, which number approx. 4500 species, pose no danger to humans. However, representatives of the spider family (e.g. Latrodectus or Loxosceles), whose bites are of medical importance, can also be found on our continent. These spiders are mainly found in the Mediterranean basin. For example, cases of bites by the hermit spider Loxosceles rufescens have been reported (in Greece, Italy, France). Such a situation is dangerous, as it can lead to soft tissue necrosis [1].

The species living in Poland, although almost all have venomous fangs and are capable of biting, are among the shy ones and avoid encounters with humans. The greater angleworm, coastal marshmallow and armed thornback are virtually the only species we may encounter on a daily basis [2].

However, it is predicted that an increasing number of alien spider species may reach Europe as stowaways, such as with cargo carried on ships [1]. The Ukrainian tarantula (Lycosa singoriensis), which is the largest spider in Central Europe and can bite painfully, has already been observed in the border area [2].

Are you sure it’s a spider?

Meanwhile, even medics are not properly trained to identify potentially dangerous species. In addition, there is no characteristic clinical picture that corresponds to a spider bite. There is also a lack of diagnostic tests to diagnose such a bite. The only thing that can be relied on is the typical mark on the skin left by spider fangs (in the form of two small dots 1-2 mm apart). Therefore, formally diagnosed cases are very few [1].

French researchers were tempted to analyze bite cases reported over 11 years. The researchers found that identification of the species, or at least confirmation that the perpetrator was indeed a spider, was possible in less than 30% of such incidents. Most people reported at least one skin symptom after a bite, and a large proportion of these symptoms were neurological in nature (such as local skin sensory disturbances and feelings of numbness) [3].

A two-year study in Switzerland identified a total of 19 bites. Most of them occurred indoors, during attempts to remove the spider or as a result of accidental squeezing. Adult female spiders of five different species were responsible for the bites. All the spiders were synanthropic, that is, living near people and even inside their dwellings. They were small-sized individuals. Nevertheless, it is assumed that a spider must have a body length of at least 10 mm to be able to pierce human skin at all [1].

Bite symptoms

The bites described in the Swiss study produced relatively mild symptoms:

• pain (acute, immediate, local, moderate to severe, comparable to a wasp sting or stronger, lasting up to several hours),
• swelling (limited and temporary),
• redness of the skin [1].

The incidence of systemic symptoms (e.g., shortness of breath, chills, sweats, vomiting, fever, cardiac arrhythmia), lasting up to 24 hours, has been estimated at 10-20% of cases [1].

Neurotoxic venom, which is an extremely complex mixture containing thousands of different components, is responsible for all symptoms after a bite. The venom components protect the venom gland from microbial colonization, facilitate digestion, but most importantly enable paralysis of the victim [4].

The smallest molecules present in spider venom are neurotransmitters. The same ones that are also found in the human body. These include serotonin, histamine, tyramine and glutamic acid [4]. The concentration of histamine in the venoms of different spider species can vary by up to 20 times [1]. Other important components hidden in the venom sac are acylpolyamines, or neurotoxins, which block selected receptors in the nervous system [4,5]. Research is underway to explore the possibility of using their properties in drug production [5].

In contrast, in most spiders, the key components of venom are proteins. Some of the large proteins immediately disrupt the physiology and metabolism of their prey. Others, distribute neurotoxins and thus induce paralysis [4].

Black Widow

The black widow (Latrodectus spp.) releases a toxic compound containing the peptide α-latrotoxin during a bite. It is the α-latrotoxin that “unseals” cell membranes, leading to a rapid efflux of calcium from the cell. The result is acute pain and convulsions, and even death in the final stage [4].

Spider venoms contain up to dozens of different proteins [4]. Do these proteins have sensitizing potential? It’s not impossible, although the topic is still very poorly studied. There are only references in the scientific literature to suspected anaphylaxis or angioedema after a spider bite. These suspicions mainly apply to the hunting spider (Heteropoda maxima), which is found in warm climates such as the southern states of the US [6,7]. There is evidence to suggest that necrotic lesions following a hunting spider bite may result from a delayed hypersensitivity reaction [8].

Although there are no reports of allergy caused by the black widow spider, at least two cases of anaphylaxis are known to have occurred after application of this spider’s antitoxin (i.e., the antidote to its bite) [6,7]. Moreover, different types of spiders have been confirmed to cause anaphylactic reactions in dogs. Therefore, it is presumed that similar symptoms in humans are possible [7].

Anaphylaxis without a bite?

An interesting incident occurred in Australia, where a patient’s contact with a spider caused hives all over his body and hypotension. There was no bite – the spider merely moved across the man’s skin. The contact lasted about five minutes. Similar reactions have been reported before, the perpetrators were exclusively large spiders from the bird family (Theraphosidae). In the Australian man, the reaction was probably caused by a hunting spider [8].

It is important to remember, however, that even a bite from a native spider species can cause us considerable problems. Sometimes a secondary bacterial infection develops within the skin lesion caused by the venom. In such cases, antibiotic therapy is necessary. Moreover, neurological symptoms, such as sensory disturbances or paresthesias, can persist for up to several months [2]. Increased pain can also last a long time – up to several days.

Particularly painful is a bite from an armyworm, which lives on tree branches, bushes and low vegetation (it can be compared to a hornet bite). Sometimes the pain extends far beyond the site of the bite, such as from the tip of the finger to the forearm [9].

Aleksandra Lipiec 

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translation: Julia Majsiak