Loxoscelismo by G.Bertelli

Generality

Loxoscelismo is a term used to indicate the skin and / or systemic reaction caused by the bites of spiders of the genus Loxosceles, which include the hermit spider and the violin spider .

The bite of Loxosceles spiders is strongly poisonous and represents the only arachnological cause demonstrated by dermonecrosis . In some circumstances, in fact, the tissues in which the poison is inoculated undergo degeneration ( necrosis ), which evolves into a long-lasting ulcer and leaves deep scars . The skin lesions of loxoscelismo are mainly due to the action of sphingomyelinase D, a hemolysing and necrotizing enzyme.

Commonly, loxoscelismo involves fever, asthenia, nausea and vomiting and can also occur with more serious systemic reactions.

What's this

Loxoscelism is a pathological condition resulting from the bite of a spider of the genus Loxosceles, such as:

Loxosceles reclusa, known as a brown hermit spider or brown recluse spider;
Loxosceles rufescens, also called violin spider ;
Loxosceles laeta, known as the Chilean hermit spider .

Although the bites of Loxosceles are generally mild, the inoculated venom can cause long-lasting ulcerative lesions or more serious systemic reactions.

The healing of loxoscelismo is very slow and can take even a few months, with possible complications from bacterial over-infections.

Loxoscelismo: why does the spider bite?

The spider bite is a lesion, also known as arachnidism, which results from the close encounter with an arachnid (ie when the latter is found in close contact with the victim's skin). Man is not among the potential prey of these animals, which tend to hide in their shelters or to run away when disturbed. Therefore, the spider bite is a completely accidental occurrence and occurs mostly when the animal is inadvertently touched, crushed or trampled. Although spider bites are harmless in most cases, it should be noted that this event can sometimes involve necrotic wounds and systemic toxicity and is only rarely fatal.

Causes

Loxoscelismo is a dermo-necrotic and / or systemic reaction induced by spider species, belonging to the genus Loxosceles .

Strongly toxic, the venom of these arachnids has a haemolizing and necrotizing action on the affected tissues and, in susceptible individuals, can give rise to the so-called loxoscelismo, which leads to the formation of an ulcer . This lesion can extend for a few centimeters and, after medical treatment, tends to heal over several weeks, leaving in its place a more or less extensive necrotic scar .

Spiders belonging to the genus Loxosceles are widespread throughout the world, but their distribution is strongly concentrated in the western hemisphere, particularly in the tropical urban regions of South America. In Italy, arachnids capable of causing loxoscelism are present mainly in the Mediterranean area .

In homes, these spiders prefer dark and sheltered environments, rarely disturbed (eg behind furniture, skirting boards, under cardboard boxes or even inside gloves, shoes, floors and basements, etc.), while outdoors they are holed up in crevices and fissures, under rocks or in the bark of dead trees.

Note: how the spider inoculates the poison

The buccal apparatus of the spider is designed to inject the poison into the victims - usually represented by insects and small animals - in order to immobilize or kill them, before feeding on them. It is not customary for arachnid to bite humans, even if this can happen, when it is trapped in the palm of the hand or is seriously annoyed. In any case, it is the poison inoculated in the wound during the bite that poses the greatest risks for humans. This can be neurotoxic (it attacks the nervous system, inducing paralysis of the prey) or necrotoxic (it affects internal organs and tissues around the wound, triggering a partial digestion of the part involved). Some spiders are considered to be very dangerous precisely because they possess poisons that are particularly harmful to humans, even in the small amount that can be injected with a single bite. Fortunately, not all spider bites involve poison inoculation.

Loxoscelismo and properties of the venom of Loxosceles spiders

The loxoscelismo is caused by the inoculation of cytotoxic secretions through the bite, the most important component of which is the ﬁ ggomielinase D. This enzyme is considered an important factor of dermonecrosis and complement-mediated hemolysis .

At the local level, the ﬁ ggomielinase D induces a series of biochemical reactions that determine, during inoculation:

Activation of the complement system and recruitment, for chemotaxis, of neutral thread leukocytes;
Induction of apoptosis of keratinocytes and other cells;
Generation of powerful metalloproteinases that degrade collagen and elastin;
Lysophosphatidic acid production, in turn responsible for:
- Pro-in ﬂ ammatory response;
- Platelet aggregation;
- Increased vascular permeability.

The reaction at the base of cutaneous loxoscelismo tends to affect the thickness of the dermis and may involve the subcutaneous layer, but generally does not pass the aponeurosis (ie the thin membrane located just below the skin).

The loxoscelismo represents a dangerous condition especially for:

Bite location;
Necrotic area extension;
Indirect risks of pathologies affected by the bite subject (allergies, heart diseases, diabetes, haematological diseases, neurological diseases, etc.).

Symptoms and Complications

The severity of the bite and of the loxoscelism that follows depends on the type of arachnid one came into contact with (violin spider, hermit etc.) and the dose of inoculated poison .

In most cases, the effects are not serious: the spider bite generally causes mild disturbances, similar to those of insect bites, that is an irritation with redness, swelling and local pain. Less often, the wound on the skin can become necrotic ( cutaneous loxoscelism ) and signs of toxicity may occur ( systemic loxoscelism ).

Skin loxoscelism

In the immediate future, the bite of the violin spider or the hermit spider may not be felt by the victim, so it is painless or causes only modest discomfort, and there are no obvious alterations in the affected area. Sometimes, the site can be identified by two small signs, similar to a skin puncture with surrounding erythema .

The loxoscelismo can give the first signs of itself after about 10-20 minutes from the inoculation of the poison, when a very intense burning type arises. The injured area becomes red, as well as itchy, and often develops a central pallor.

In the following hours, the area around the bite may appear:

Swelling;
Decrease in sensitivity;
Tingling.

After 2-12 hours, the pain increases and follows the appearance of a vesicle, generally with a hemorrhagic content, surrounded by a rhyme of livid or whitish skin and by an extended, more evident asymmetric erythematous area, with a centrifugal extension (commonly called " sign "). red, white and blue ").

In most cases, this lesion is self-limiting and resolves without further complications in about a week.

However, in some patients, over the next 48-72 hours, the bladder widens and breaks, giving rise first to an open sore ( ulcer ), then to a thick black crust ( eschar ), which can leave a important scar . A fully developed loxoscelism necrotic lesion usually has a diameter between 1 and 2 cm, although the loss of the skin may be more extensive.

Some patients develop a morbilliform urticaria or rash in the hours following the bite.

Systemic loxoscelism

In some cases, the necrotoxic poison inoculated with a spider bite can induce a systemic reaction, which is manifested by:

General malaise;
Myalgia;
Fatigue;
Nausea and vomit;
Abdominal pain;
Headache;
Dizziness;
Chills;
Excessive sweating;
Articolar pains;
High fever;
Blood disorders, including hemolysis (rupture of red blood cells) and reduction of platelets.

In the most serious cases, systemic loxoscelism can induce:

Cardiac arrhythmias;
Hypertensive crisis;
Lymph node pain;
Pharyngitis;
Abundant salivation (sialorrhea);
Disorientation, confusion and loss of consciousness;
Kidney failure.

Visceral loxoscelism

In addition to cutaneous and systemic loxoscelism, it is important to point out the presence of a visceral form, not documented, to date, in Europe. This clinical picture can manifest itself, within a few hours of the bite, resulting dangerous and potentially fatal.

Possible complications

Rare complications of loxoscelism include angioedema, acute hemolytic anemia, disseminated intravascular coagulopathy, rhabdomyolysis, myonecrosis, renal failure, coma and death.
In previously sensitized people, the spider bite can induce a local allergic reaction, characterized by erythema, extensive edema and pain. Other times, the allergic reaction to the spider bite can involve different parts of the body and induce systemic manifestations, including: generalized urticaria, angioedema, respiratory difficulties, palpitations, feeling of nausea and abdominal cramps. In severe cases, an anaphylactic shock may develop after a spider bite. This is characterized by a marked and persistent reduction in arterial pressure, which can lead to numbness or loss of consciousness, dizziness and cardiovascular arrest.

Diagnosis

The diagnosis of loxoscelismo is rather complex, especially if a spider bite is not evident as a medical history (it must be remembered that the contact with the arachnid can go unnoticed).

The evaluation procedure involves the examination of the involved skin area, in order to identify any signs of toxicity or necrosis. When they come to the attention of the doctor, loxoscelismo may appear similar to burns or chemical burns.

Warning! The bite of a spider should never be underestimated and some symptoms must be interpreted as alarm bells .

The sudden onset of these manifestations or their progressive worsening, must induce to consult the doctor within a short time :

The area of the spider bite is sore, red, hot, swollen and surrounded by a pale halo, red-bluish or purplish;
At the site of the lesion and in the neighboring tissues, itching, changes in sensitivity and crusts of dark color (eschar) appear;
After the spider bite, systemic symptoms begin, such as nausea, vomiting, muscle weakness or fever.

Treatment and Remedies

The treatment of loxoscelismo is controversial and not completely shared. No intervention has been shown to reduce morbidity or improve outcomes after a spider bite Loxosceles . In particular, corticosteroids, colchicine, nitroglycerin and surgical excision have no value in counteracting dermonecrosis.

If the symptoms of loxoscelismo appear severe immediately, instead, call 118 or contact a poison control center . Depending on the type of spider that caused the bite, in fact, it may be necessary to administer a specific antidote, capable of blocking the action of the poison.

For moderate to severe ulcerative or necrotic wounds resulting from loxoscelism, it may be necessary to have surgery .

Warning! If possible, capture the spider in a closed jar and take it to the emergency room for recognition. Even if crushed or trampled, the arachnid can be identified.

Loxocelism usually resolves within 10 days of the bite and most lesions heal within a few weeks, without scarring. Some necrotic areas take months to completely heal.

Permanent scars or the requirement for surgical repair are quite rare.

First intervention and treatment of mild loxoscelism

In general, the initial therapeutic approach involves applying cold compresses or immersing the affected area in fresh water to relieve the pain or discomfort associated with the spider bite.

Furthermore, depending on the case, it may be useful:

Let the affected part rest, compress and keep up (when the limbs are involved);
Do not manipulate or engrave the site of the spider bite;
Wash the wound thoroughly with soap and water;
Do not apply aggressive disinfectants;
Pay attention to the appearance of symptoms, even if initially the spider bite was not felt (possibly documenting the lesion with a series of photographs, to monitor the evolution).

When the symptoms of the spider bite tend to persist, however, it is always necessary to consult the doctor, who can indicate the use of analgesics (to control the strong pain symptoms) or the application of cortisone- based creams (to reduce inflammation and itching). To minimize the urticarial lesions related to loxoscelism, the doctor may also recommend the use of antihistamines, topical corticosteroids or both .

Prevention of infections

In cases of suspected over-infection of the loxoscelism lesion, the use of broad-spectrum antibiotics may also be indicated. To minimize the risk of infection, skin ulcers must also be cleaned daily with a iodopovidone solution and immersed 3 times a day in sterile (physiological) saline solution. Depending on the case, the doctor may also prescribe the application of a local antibiotic ointment (eg polymyxin, bacitracin and neomycin). To avoid dermonecrosis secondary to loxoscelism, the use of tetracycline has been suggested, but efficacy is unproven.

Loxoscelismo: surgical approach

The management of necrotic areas caused by the bites of Loxosceles spiders is similar to that of loxoscelism ulcers, so the lesions are cleaned and bandaged daily. If necessary, surgical resection should be postponed until the necrotic part is completely enclosed, a process that can take several weeks.

In cases of loxoscelism with significant wound necrosis, plastic-reconstructive surgery may be necessary.

How to prevent spider bites

The adoption of certain behaviors can help to minimize the risk of being bitten by a spider. First of all, the removal of these animals is done by direct capture or by suction with commonly used appliances . Instead, chemical disinfestation techniques should only be used as a last resort.

In general, to prevent the spider bite it is good to observe the following precautions: