roko
05-03-2013, 09:21
Spider venom poisoning constitutes a disease state characterized by a set of signs (observable physical or objective evidence of disease) and symptoms (complaints that the bite victim relays to the physician, etc.), which lead to the diagnosis of spider envenomation. Traditionally, disease states induced by spider bite have been assigned specific names, according to the genus of spider which causes the poisoning. For example, poisoning by the widow spiders (genus Latrodectus) is termed latrodectism, while poisoning by the recluse spiders (genus Loxosceles) is known as loxoscelism; thus, poisoning caused by the hobo spider, Tegenaria agrestis, may be properly termed tegenarism. While not all species in any given spider genus may induce significant poisoning, and while signs and symptoms may differ from species to species in a genus, this nomenclature has proven useful in categorizing different types of spider envenomation.
Hobo spider poisoning (tegenarism) does not invariably develop following a bite by a hobo spider. A large percentage (perhaps 50% or more) of defensive bites by the hobo are "dry", and no venom is injected when the spider bites (see A Word About Bites and Stings for more on this). Hobo spiders, like many other venomous creatures, are more likely to incorporate venom in a food getting bite than in a defensive bite. Typically, defensive bites by the hobo spider are lightning fast, the spider opening its scissor-like fangs, closing them together into the tissue of the victim, and then withdrawing rapidly. Very often the bite itself is painless, although this varies depending upon the circumstance and location of the bite, and upon the psychological state of the victim. Most spider bites are single, not in rows or patches like those of some parasitic arthropods; multiple bites do occasionally occur, such as when the spider is trapped between skin and clothing, and cannot escape.
When envenomation does occur from the bite of a hobo spider, local and/or systemic manifestations may appear. The severity of these phenomena are dependent to a degree on the age and sex of the biting spider: In laboratory experiments the venom of the male hobo spider produces more severe effects than that of the female, and evidence exists suggesting that the venom of subadults may be more toxic than that of adults. The local effects, which appear following most hobo spider envenomations, represent a type of necrotic arachnidism, which is almost identical to the local effects produced by brown recluse spider, Loxosceles reclusa, poisoning. Typically, immediately following envenomation, a large (several cm.) area of redness (erythema) forms around the bite site: This usually disappears within a few hours, leaving a small reddish induration (hardened area), which is not dissimilar to the classical "mosquito bite". Within 24 to 48 hours blistering may occur at the bite site. Within an a additional 24 hours these blisters may rupture, leaving an open ulceration. Within a few days of ulceration, if left uncovered, eschar or "scab" formation begins to develop over the lesion, and by three weeks post-bite this becomes pronounced, giving the lesion a "target and bulls-eye" appearance. Following this, the "scab" is sloughed and the lesion generally heals, leaving a scar, within 45 days of the original bite. In some instances, particularly when the bite is delivered in an area of fatty tissue, such local lesions may become deep and extensive, and may not heal for two to three years, as exemplified in the photo below.
Other long-term physical effects, such as intractable burning pain, damage to blood vessel valves, and cyst formation occasionally occur in conjuntion with local lesion development. The lesion that results is sometimes oblong or multiple, resulting not from more than one spider bite, but rather from gravitational drift, which moves venom components downward, away from the bite site. The process which causes the local phenomenon of necrotic arachnidism involves circulatory disturbances which result in ischemia, or lack of adequate blood flow in the affected tissues. Following venom injection, rapid coagulation of blood occurs in the smaller blood vessels of these tissues. This produces a centralized area which does not receive enough blood, and the area literally dies as a result of oxygen starvation.
Systemic, or generalized effects are seen in about 45% of persons envenomated by hobo spiders. The most common reported symptom is severe headache, which usually does not respond to over the counter analgesics (aspirin, which can prolong bleeding time, should not be used for hobo spider bite induced headaches). In addition to this, victims may experience a dry mouth, nausea, weakness and lethargy, dizziness, visual disturbances, hallucinations, joint pain and/or other undesirable effects. As with many types of complex poisoning, most victims of systemic tegenarism do not experience all of these phenomenon, but that is dependent upon the severity of the poisoning. About 15% of envenomated subjects are poisoned severely enough to require hospitalization: In rare cases aplastic anemia (bone marrow failure) can develop several weeks after the bite, which results in a fatal outcome. Another rare but dangerous condition that has been seen following hobo spider envenomation is the development of severe intractable vomiting accompanied by secretory diarrhea.
Some cardinal rules apply to persons that have been bitten by, or think that they have been bitten by a venomous spider. Above all, if you are bitten by any spider, and actually catch the spider in the act, always capture the spider for identification by a qualified arachnologist. Never discard a spider that has definately bitten a human. In the case of the hobo spider, not only is positive species identification important, but so is a determination of the spiders sex and age; these factors can help predict the severity of potential poisoning, and assist the attending physician in charting a course of treatment. Preserve the spider (or whatever parts of it remain) and take it to the clinic with you. If you suspect that you have been bitten by a dangerously venomous spider, see a physician. Most suspected spider bites in the United States turn out to be other conditions. The vast majority of spiders are harmless and beneficial.
Hobo spider poisoning (tegenarism) does not invariably develop following a bite by a hobo spider. A large percentage (perhaps 50% or more) of defensive bites by the hobo are "dry", and no venom is injected when the spider bites (see A Word About Bites and Stings for more on this). Hobo spiders, like many other venomous creatures, are more likely to incorporate venom in a food getting bite than in a defensive bite. Typically, defensive bites by the hobo spider are lightning fast, the spider opening its scissor-like fangs, closing them together into the tissue of the victim, and then withdrawing rapidly. Very often the bite itself is painless, although this varies depending upon the circumstance and location of the bite, and upon the psychological state of the victim. Most spider bites are single, not in rows or patches like those of some parasitic arthropods; multiple bites do occasionally occur, such as when the spider is trapped between skin and clothing, and cannot escape.
When envenomation does occur from the bite of a hobo spider, local and/or systemic manifestations may appear. The severity of these phenomena are dependent to a degree on the age and sex of the biting spider: In laboratory experiments the venom of the male hobo spider produces more severe effects than that of the female, and evidence exists suggesting that the venom of subadults may be more toxic than that of adults. The local effects, which appear following most hobo spider envenomations, represent a type of necrotic arachnidism, which is almost identical to the local effects produced by brown recluse spider, Loxosceles reclusa, poisoning. Typically, immediately following envenomation, a large (several cm.) area of redness (erythema) forms around the bite site: This usually disappears within a few hours, leaving a small reddish induration (hardened area), which is not dissimilar to the classical "mosquito bite". Within 24 to 48 hours blistering may occur at the bite site. Within an a additional 24 hours these blisters may rupture, leaving an open ulceration. Within a few days of ulceration, if left uncovered, eschar or "scab" formation begins to develop over the lesion, and by three weeks post-bite this becomes pronounced, giving the lesion a "target and bulls-eye" appearance. Following this, the "scab" is sloughed and the lesion generally heals, leaving a scar, within 45 days of the original bite. In some instances, particularly when the bite is delivered in an area of fatty tissue, such local lesions may become deep and extensive, and may not heal for two to three years, as exemplified in the photo below.
Other long-term physical effects, such as intractable burning pain, damage to blood vessel valves, and cyst formation occasionally occur in conjuntion with local lesion development. The lesion that results is sometimes oblong or multiple, resulting not from more than one spider bite, but rather from gravitational drift, which moves venom components downward, away from the bite site. The process which causes the local phenomenon of necrotic arachnidism involves circulatory disturbances which result in ischemia, or lack of adequate blood flow in the affected tissues. Following venom injection, rapid coagulation of blood occurs in the smaller blood vessels of these tissues. This produces a centralized area which does not receive enough blood, and the area literally dies as a result of oxygen starvation.
Systemic, or generalized effects are seen in about 45% of persons envenomated by hobo spiders. The most common reported symptom is severe headache, which usually does not respond to over the counter analgesics (aspirin, which can prolong bleeding time, should not be used for hobo spider bite induced headaches). In addition to this, victims may experience a dry mouth, nausea, weakness and lethargy, dizziness, visual disturbances, hallucinations, joint pain and/or other undesirable effects. As with many types of complex poisoning, most victims of systemic tegenarism do not experience all of these phenomenon, but that is dependent upon the severity of the poisoning. About 15% of envenomated subjects are poisoned severely enough to require hospitalization: In rare cases aplastic anemia (bone marrow failure) can develop several weeks after the bite, which results in a fatal outcome. Another rare but dangerous condition that has been seen following hobo spider envenomation is the development of severe intractable vomiting accompanied by secretory diarrhea.
Some cardinal rules apply to persons that have been bitten by, or think that they have been bitten by a venomous spider. Above all, if you are bitten by any spider, and actually catch the spider in the act, always capture the spider for identification by a qualified arachnologist. Never discard a spider that has definately bitten a human. In the case of the hobo spider, not only is positive species identification important, but so is a determination of the spiders sex and age; these factors can help predict the severity of potential poisoning, and assist the attending physician in charting a course of treatment. Preserve the spider (or whatever parts of it remain) and take it to the clinic with you. If you suspect that you have been bitten by a dangerously venomous spider, see a physician. Most suspected spider bites in the United States turn out to be other conditions. The vast majority of spiders are harmless and beneficial.