1. Black Widow Spider
Alpha Latrotoxin
By:
Shireen Abdulrahman

2. Introduction
• Arachnophobia, an irrational fear of spiders and is considered
among the most common of all phobia.
• Of the 30,000 types of spiders, the black widow is probably
the one best known and feared.
• Latrodectus mactans, the black widow, is a highly venomous
species of spider in the genus Latrodectus.

3. Introduction
• Members of the “widow” family of spiders are found all over
the world and are believed to account for the majority of fatal
spider bites.
• The species is native to the United States of America, Canada
and Mexico.
• The female black widow's venom is particularly harmful to
humans (males almost never bite humans).

4. Black widow spider
• The name of the black widow spider, Latrodectus mactans, is
a mixture of Latin and Greek, meaning “deadly biting robber”
(from latro—robber, bandit; δαγκάνω—to bite; macto—to
slay).
• The widow spiders get their name from the females’
supposed eating of the male after mating. In nature, the great
majority of males get away.
• The black widow spider is also called“The Hourglass Spider”
because of the red hourglass shaped mark on the female’s
abdomen.

5. Fig: The hourglass marking of an adult female black widow. Latrodectus sp.

6. Black widow spider
• The widow spiders have eight eyes arranged in two rows of
four and their vision is quite poor.
• Males, generally considered harmless to vertebrates, are
generally about half the size of females.
• The bite of a black widow spider is poisonous. It causes severe
pain and other serious clinical symptoms in humans, making
this spider medically important.

7. Fig: Female and male black widow spiders Latrodectus mactans.

8. Black Widow Spider Venom
• Latrodectus venom is produced by glandular cells in the spider's
chelicerae.
• In a process called holocrine secretion, these cells disintegrate and
their content is released into the lumen of the gland.
• Although black widow spiders are not large, their venom is
extremely potent. It is fifteen times more potent than that of the
rattlesnakes and is also reported to be much more potent than the
venom of cobras and coral snakes.
• Black widow venom evolved mainly to immobilize and/or kill
insects, the spider's natural prey.

9. Black Widow Spider Venom
• Toxicity against vertebrates is likely to have evolved as a
means to protect the species against predation and
accidental crushing.
• The actual amount of venom injected, even by a mature
female, is very small in physical volume. The males, being
much smaller, inject far less venom.

10. Black Widow Spider Venom
• There are a number of active components in the venom:
1. Latrotoxins
2. A number of smaller polypeptides - toxins
interacting with cation channels which display
spatial structure homology - which can affect the
functioning of calcium, sodium, or potassium
channels.
3. Adenosine
4. Guanosine
5. Inosine
6. 2,4,6-trihydroxypurine.

11. Black Widow Spider Venom
• Latrotoxin is the active component within the venom, and
more specifically, alpha-latrotoxin is the toxin that affects
vertebrates.
• The venom of the black widow spider is a neurotoxin that
alters the structure and function of nerve terminals without
producing any significant local reaction.

12. Alpha latrotoxin
• Latrotoxins are the main active components of the venom
of spiders of the genus Latrodectus (widow spiders).
• They are neurotoxins and are responsible for the symptoms
of latrodectism.
• The best-studied latrotoxin is alpha-latrotoxin, which acts
presynaptically to release neurotransmitters
acetylcholine, norepinephrine, and GABA from vertebrate
sensory and motor neurons, as well as on endocrine cells.
• The release of these neurotransmitters leads to the clinical
manifestations of envenoming.

13. Alpha latrotoxin
• If enough venom is injected into a person's body, initially a
severe pain in local muscle groups occurs, and the pain
then spreads to regional muscle groups. The spread relates
to the toxin initially being carried by the lymphatic system
until it reaches the blood stream.
• Once in the blood, the venom is moved by circulation,
causing its toxins to be deposited in nerve ends where
nerves insert into muscle.
• The venom acts at nerve endings to prevent relaxation of
muscles, causing tetany — constant, strong, painful muscle
contractions.

14. Structure
• Alpha-latrotoxin is approximately 130kDa and is a stable
dimer that is able to be tetramerized.
• As discovered by the 3D structure from electron microscopy,
there are three distinct domains (head, body wing) of this
toxin. The N-terminal wing (36 kDa), the body (76 kDa), and
the C-terminal head (18,5 kDa).
• The α-LTX monomer forms a dimer with another α-LTX
monomer under normal conditions.

15. Fig: The domain structure of alpha latrotoxin

16. Structure
• The dimers are able to spontaneously form tetrameters which
requires conformational changes.
• These conformational changes are induced by divalent
cations, including magnesium or calcium which are also
necessary for latrotoxin activity.
• Tetramer formation activates toxicity.

17. Structure
• The wings of the dimer are facing in opposite directions which
makes it unlikely that it will be able to pierce the membrane.
• The tetramer is able to insert itself into the membrane
because of its hydrophobic or lipophilic bases and these bases
permeate the membrane.

18. Fig: 3D reconstruction of latrotoxin oligomers (top). Side view of tetramer
inserting itself into lipid (bottom)

19. Mode of action
• α-LTX in its tetrameric form interacts with receptors
(neurexins and latrophilins) on the neuronal membrane,
which causes insertion of α-LTX into the membrane.
• Once the tetramer is inserted into the cell membrane it
induces exhaustive neurotransmitter exocytosis from
vertebrates through two calcium-dependent mechanisms
(membrane pore formation and signaling via latrophilin) and a
yet to be defined calcium-independent mechanism.

20. Fig: Example of synaptic cleft and action of neurotransmitter with its receptor.

21. 1) Pore formation
• The pores formed by α-LTX in the membrane are
permeable to Ca2+ and therefore allows an influx of Ca2+
into the cell.
• This influx into an excitable cell stimulates exocytosis
directly and efficiently.
• The cation influx is proportional to the number of pores
formed.
• Also Ca2+ strongly facilitates the forming of the tetramers
and so its pore formation.

22. 1) Pore formation
• The pore is also permeable to neurotransmitters which causes
massive leakage of the neurotransmitter pool into the
synpatic cleft.
• Alongside the influx of Ca2+, the channel is not very selective,
allowing Na+, K+, Ba2+, Sr2+, Mg2+, Li+ and Cs+ to pass the
membrane too.
• The pore is not only permeable for cations, but also for water
which causes nerve terminal swelling.

23. 2) Signaling via Receptors
• Alpha-LTX protein, is capable of very tight binding with a
number of different membrane proteins in several
different types of neurons.
• Three receptors for α-latrotoxin have been described:
1. neurexin
2. latrophilin
3. Protein tyrosine phosphatase sigma (PTPσ).
• The following mechanism is suggested for receptor-
mediated effects:

24. 2) Signaling via Receptors
• The toxin stimulates a receptor, most likely latrophilin.
• Latrophilin in turn activates the downstream effector
phospholipase C (PLC) which indirectly induces release of
Ca2+ from intracellular stores.
• This rise in cytosolic Ca2+ may increase the probability of
release and the rate of spontaneous exocytosis.
• Thus latrophilin with α-LTX induces the effect of exocytosis of
transport vesicles. The exact mechanism is yet to be
discovered.

25. `
Fig: Alpha latrotoxin mechanism of action

26. Venom toxicity
• It is notable that the reported LD50 of the best-studied and
most stable LTX, α-LTX, ranges widely from 4.3 to 20 to 95
μg/kg.

27. Latrodectism
• Latrodectism is the clinical syndrome caused by the
neurotoxic venom, that can be injected by the bite of any
spider that is a member of the spider genus Latrodectus.

28. Symptoms
Symptoms occur in three main phases: exacerbation phase, dissipation phase and
residual phase.
1) Exacerbation phase
During the first 24 hours after a bite:
• Severe pain in muscle groups local to the bite.
• Muscle cramping, primarily in the abdomen, back and thighs.
• Headache, dizziness, tremors, salivation, diaphoresis (excessive
sweating), nausea and vomiting.
• Anxiety, fatigue, insomnia.
• Lacrimation (tearing of the eyes).
• Migratory arthralgia (joint pain).
• Tachycardia (rapid heartbeat), bradycardia (very slow heart
beat), restlessness, hypertension (elevated blood pressure), Tachypnea
(hyperventilation).

29. Symptoms
In some rare and extreme cases, severe complications can arise:
• Spontaneous abortion, preterm labor
• Priapism
• Acute renal failure (failing of kidney function).
• Myocarditis, rhabdomyolysis, paralysis.
• Shock, coma, and death.
Symptoms that may be present at or near the wound:
• Rash, slight erythema (redness of skin), Piloerection (goose bumps).
• Mild edema (swelling due to excess fluid).
• Lesion or mild infection (rare).

30. Symptoms
2) Dissipation phase
During the first 1 to 3 days after the bite:
• Symptoms start to decline.
3) Residual phase
During the following weeks or months:
• Muscle spasm, tingling, nervousness and weakness. There is a
potential risk of paralysis.

31. Latrodectism
Mortality
• Although severe symptoms such as shock and coma are
known to have happened, death due to latrodectism is rare.
Young children appear to be at highest risk for a lethal bite.
Prognosis
• The vast majority of victims fully recover without significant
sequela.

32. Treatment
Self-Care at Home
• The options for home care are limited.
• Both cold and warm compresses have been recommended, as
have hot baths.
• Over-the-counter pain relievers such as
acetaminophen and ibuprofen may be of value in mild cases.

33. Treatment
Medical Treatment
• Standard treatments usually involve symptomatic therapy .
• The person bitten by a black widow spider, who has pain severe
enough to seek treatment at an Emergency Department, will
require narcotic pain relief.
• Muscle relaxants given by injection may also be of value.
• Although calcium gluconate given through an IV has long been
advocated, it does not seem to produce much relief of symptoms.

34. Treatment
• The antivenin available for treatment of black widow spider
bites is derived from horse serum.
• The venom produced by various species of black widow
spiders is similar, so the antivenin (antivenin) prepared against
one venom is effective against the others.
• Some experts recommend that antivenin be used in any
severe bite because one vial of the antitoxin produces
significant and rapid relief of symptoms.

35. Side effects
• Horse serum-based antivenin carries a significant risk of
a severe allergic reaction which can be life-threatening.
• Skin testing before the serum is administered is therefore
recommended.

36. Follow-up
• Follow-up is always necessary in cases where antivenin is
used.
• Although serum sickness is uncommon with single-vial doses
of horse serum, it may occur 7-12 days after exposure and is
characterized by skin lesions, fever, pain in the joints, and
swollen lymph glands.
• The process is self-limited, goes away in 2-3 weeks, and may
be treated with antihistamines and steroids.