Other important points to consider
(With explanation of terms and methodology)
Other important points to consider
(With explanation of terms and methodology)
The same set of information is subjected to different interpretation and analysis. It is, however, important for the reader to know some basics before a critical conclusion is drawn. Below are some of the points I personally noted. For the general reader, look elsewhere as things get pretty technical even with simplification.
On LD50/Potency
LD50 (lethal dose 50) is the quantity of venom (injected via a predetermined
administration route) required to kill 50% of the animals in a controlled test. It is a
standard measure of potency of the toxins. I note the following
1) In most of the reference to venom, laboratory mice is the animal used
2) The units used is milligram of venom per kilogram of mouse (expressed as mg/kg).
Other units are microgram per kilogram (ug/kg) and milligram per mouse (expresses as
mg/mouse). A lab mouse usually weight about 16-30 grams and the lower estimate or a
convenient figure of 20gm is commonly used. Subcutaneous routeis generally used.
A sub point is that a slight increase from dose of LD50 will generally cause a
disproportionately high increase in death such that at 1.5 times the LD50 dose, most, if
not all, mice would be killed. (LD100)
3) Scorpion venom potency is subjected to individual variation. Different individual scorpion usually has slight difference in composition and quantity of venom.
4) Individual scorpion venom potency may also be affected circadian rhythm and physiological state. Therefore time and condition of test is important
5) Individual mice tolerance to same venom can be very different. As such an average of a large number of mice is generally more accurate
6) Mice of different genetic pool usually exhibit different tolerance as well. This may account for the vastly different results among researchers on the same scorpion from same region.
7) Scorpions of the same species but different locality (geographic race) may have different venom potency. This is borne out by the example of Buthus occitanus which is considered lethal in North Africa but not so in South France. Note the difference in LD50 for B.occitanus paris and B.occitanus tunetanus in my LD50 chart. Rattler snake apparently also shows this locality based difference in toxicity. The same might be applied to Centruroides exilicauda though I'm not sure.
8) Different animals shows very great difference in tolerance to the same venom. An example using Latrodectus mactans tredecimgutttatus venom (Bettini and Maroli) shows LD50 as follows:
Animal LD50
(mg/kg) subcutaneous
Frog 145+-32
Blackbird 5.9+-1.7
Pigeon 0.36+-0.7
Cockroach
2.7
Housefly
0.6
Guinea
pig
0.075
Mouse
0.9
Rat
0.21
We see here a big difference in potency even between mouse and rat and the difference between frog and guinea pig is simply incredible. However, since the exact species of animal is not stated and the condition of test not known, such difference cannot be taken in its entirety. Still, it proves that venom do have vastly different impact on different animals. As such, potency to mice should be not directly interpreted as potency to man. This is the point I trying to bring home here.
9) Different routes of administration affects the result. The common known means
of administration are
(a) Oral (b) intravenous (into veins and arteries) (c) intraperitoneal (into peritoneal
cavity at the abdomen) (d) sub-cutaneous (into skin) (e) others like anal administration
is quite unlikely for scorpions............
Oral
Yes, some people drink the venom and claim immunity against scorpion venom. This
is untrue. Fact is drinking scorpion venom in an individual without oral, stomach or
intestinal ulcers/bleeding is without much effect. Drinking snake or scorpion venom
without effect IS normal. They, unlike poisonous animals eg. puffer fish, can be consumed
without problem except at incredible high dose. Just let the showman get a sting from a
lethal species and see how good his 'immunity' is....... He will most likely show similar
severe symptoms as any of us.
Intravenous (IV)
This is by far the most dangerous route of administration. The effects is
immediate with little time for the body to react and mount an immunity response against
the toxin. Generally, a higher potency is registered compared to subcutaneous or intra
peritoneal administration. It is very very rare for such stings to occur as it must
penetrate deep enough at the specific sites where main veins are to be considered
intravenous. Such stings if ever occur will be more severe. Please note that Hassan's
(1981) study on potency of scorpions are based on IV and therefore accurate comparision
with other potency is not possible.
Intraperitoneal (IP)
A sting at the abdomen deep into the peritoneal cavity is rare to say the least.
This administration is used for drug testing in animals but not for scorpion sting. There
are a small number of LD50 based on this
Subcutaneous (SC)
The most common means of administration. The site of sting in human is usually on
the hands (careless pet owners, collectors and innocent beings). In one research, 70% of
the stings occur on hand. The route of travel to the system is via the capillaries and
lymphatics beneath the skin. This is in general slower and less severe than IV.
10) Most desert scorpions has venoms of higher potency than mesic (non-desert) species. This can be easily explained by the selective pressure for conservation of fluid. A higher concentration of toxin in each gram of venom is without doubt a great advantage for scorpions in regions without much fluid.
11) Some people are more susceptible than others to scorpion sting. Children and very old man with atrophy are more susceptible for three main reasons. One, the body mass for distribution is smaller so plasma toxin concentration is higher than in an healthy adult. Two, the immunity is not mature or is compromised. As such, the abiilty to detoxify venom is reduced (longer biological half life) Three, they are often afflicted with other disease like pneumonia which can be worsen by the toxic effects. This may partially explain why death rates in poverty stricken regions is much higher.
12) Surviving lab mice cannot be used again as accuracy will be affected no matter how long has elapse. Two phenomena usually happens after the first injection, 1) increased immunity 2) increased sensitvity. In increased immunity, the mice is more tolerant to the venom while in increased sensitivity, the mice develop anaphylactic reaction to some the components thereby causing distress and death not related to the potency of the venom. Both may occur at the same time but one will predominate, Either way, the result is inaccurate. This may make Centruroides spp very dangerous as it is so common to get stung by them in America.
13) Research results done by antivenom producer or anyone with vested interest should be given tight scrutiny. There seems to be an tendency to exaggerate the potency of the venom and mortality due to the species they are producing antivenom for. There also exist quite frequently different results with regards to the curative effect of the antivenom with the antivenom producer claiming greater success than other independent experiments. However, please do not be disregard their findings based on just this possibility of selective reporting. Most are quite responsible and the apparent discrepancy might be attributed to normal variations within experiments.
Venom yield vs venom injected
1) The amount of venom is very different in each individual and varies also with species
2) A large minority of the stings are dry. This means that no venom is injected in some stings
3) The venom injected is under the scorpion's voluntary control. One sting may not contain the full quantity of venom it possess.
4) The average venom milked from scorpion per electical stimulation is about 0.1mg. This is a very small quantity.
5) Venom takes a long time to fully regenerate. The first few stings will be more severe for the simple fact that others contains much less or no venom.
6) Larger species like Heterometrus spp *may* possess more venom.
Aggressiveness, Distribution and Propensity to allergy
1) Aggressiveness though not measurable in standard units is important
when considering the danger a scorpion pose to the owner. Banded krait, Bungarus
fasciatus, possess very potent bungarotoxin. However, its reluctance to bite and
peaceful nature makes it safer to handle than non-venomous racer, Elaphe flavolineata.
As a result, I regard the aggressive fat tailed scorpion, Androctonus australis, to
be one of the most dangerous scorpion even though it may not be the most venomous. I heard
it is quite willing to sting.
2) Distribution. Species like Bark scorpion Centruroides exilicauda create such big following due to misinformation and its wide distribution. Highly venomous but reclusive and rare species is not as important than those more common species simply because stings by them is almost non-existent. Common and deadly species like Leiurus quinquestriatus and Androctonus spp got much deserving attention.
3) Propensity to allergy. The chance of one getting a anaphylactic reaction increase markedly with each sting by same species. This is oppose to the common thought that immunity can be gained from repeated stinging. Immunity DO develop but the danger of anaphylactic reaction should deter most well informed people from pushing their luck. Some substances are more likely to cause allergy. A case in point is the apamin of bees. Though potency of bee is relatively low (refer to later sections), it is one of the most dangerous animals. Many deaths are caused by bees each year and most are partially due to anaphylactic shock. This is especially true of individuals dying from a single sting as judging by potency and yield, it is unlikely.