Medicine 5th year, 11th lecture (Dr. Mohammad Shaikhani)

Bites & Stings

SNAKE BITES

Snake bite is common life-threatening in many countries. Farmers, hunters, rice-pickers are at particular risk Prompt medical treatment is vital. 3-5 million victims /year, 50 000 deaths , 400 000 amputations. 40% of bites do not produce signs of envenoming. It is difficult to predict which bites will produce symptoms or

the clinical outcome, all victims should be brought under medical care as quickly as possible.

Poisonous species of snake fall into the families. Snake venoms are complex mixtures of proteins & small

polypeptides with enzymatic activity. Snake venoms are neurotoxins, haematotoxins (haemorrhagic

or coagulopathic) or cardiotoxins often occur in combination.

Clinical features & assessment

Key questions to ask a victim are: The body part bitten? How long ago? What sort of snake? Friends / relatives will frequently bring the snake with the

patient; it should be handled as little as possible since it may only be injured rather than dead.

The amount of venom injected via a bite is highly variable, depending on the length of time since the snake last ate& its aggression.

The pattern of clinical features is shown. Snake venom detection kits are available in some countries.


The venom is detected from a dry swab of the bite site using monoclonal antibody techniques.

The 20-minute whole blood-clotting test is a useful bedside tool in remote areas; a 2-3 ml sample of venous blood from the victim is left undisturbed at ambient temperature for at least 20 minutes.

The vessel containing the blood is then tipped once & may be compared with a normal control.

If it has not clotted, there is haemostatic disturbance from systemic envenoming.

All patients should have a full blood count, urea/electrolytes, liver function tests, creatine kinase, troponins, ECG.


Snake venom detection kits are available in some countries. The venom is detected from a dry swab of the bite site using monoclonal antibody techniques. The 20-minute whole blood-clotting test is a useful bedside tool in remote areas; a 2-3 ml sample of venous blood from the victim is left undisturbed at ambient temperature for at least 20 minutes. The vessel containing the blood is then tipped once and may be compared with a normal control. If it has not clotted, there is haemostatic disturbance from systemic envenoming. All patients should have a full blood count, urea and electrolytes, liver function tests, creatine kinase, troponins and an ECG performed.







Management:

Reassuring the patient Immobilising the bitten area to minimise venom spread Identifying the snake. Application of a firm bandage to occlude lymphatic drainage

is appropriate, but tourniquets are unhelpful since they do not prevent the spread of venom & frequently applied incorrectly.

Incisions at the bite site &attempts to suck out the venom by mouth should not be made.

A large-bore IV cannula inserted on an unaffected limb. BP, coagulation,renal, neurological, cardiorespiratory status

must be monitored, as hypotension, anaphylactic shock, renal failure, respiratory distress may develop rapidly.

Management:

All patients with suspected envenoming should be observed for 12-24 hours, as the initial manifestations may be delayed, especially with elapid bites.

Pain/ vomiting should be managed symptomatically. Aspirin should not be used ,may aggravate bleeding. In severe coagulopathy with thrombocytopenia causing DIC,

large quantities of fresh frozen plasma, cryoprecipitate , platelets are required if the response to antivenin is poor.

The most appropriate therapy is timely administration of the species-appropriate antivenin when indications.

Before starting antivenin, ask about history of allergy & intradermal sensitivity test performed by injecting 0.02 ml of saline-diluted antiserum at a site distant from the bite.

Management:

The inj site is observed for at least 10 mins for the redness, hives, pruritus or other adverse effects.

The shorter the interval between inj & reaction, the greater the degree of sensitivity.

0.5 ml 1:1000 adrenaline must be available when antiv given A negative skin test does not rule out a reaction following

administration of the full antivenin dose. The rate antivenin should be based on the severity of the

case& the patient's tolerance to the antivenin. The entire initial dose should be given as soon as possible

within 4 hours of the bite. In severe envenoming, antivenin given up to 24 hours after the

bite has been shown to reverse coagulation deficits.

Management:

INDICATIONS FOR ANTIVENIN ADMINISTRATION IN SNAKE BITES

Cardiogenic shock Spontaneous systemic bleeding Incoagulable blood Neurotoxicity Haematuria Other evidence of haemolysis/rhabdomyolysis Rapidly progressive extensive local swelling Bites on digits by snakes with known necrotic venoms

SNAKE BITES

There are three types of antivenin reaction: Early anaphylactoid Pyrogenic Late. If an immediate anaphylactoid reaction occurs,

administration of antivenin should be immediately discontinued &the patient given an oral antihistamine or IM adrenaline ( 0.5 ml of 1:1000) as appropriate.

Infusion of the antivenin can be restarted, but at a slower rate. Corticosteroids are commonly given to treat serum sickness,

although their value remains to be established. Bites by large snakes may need relatively high antivenin doses,

particularly in children or small adults.

SNAKE BITES

Additional antivenin (e.g. the contents of 1-5 vials) should be administered if swelling progresses or if systemic features of envenoming increase in severity & new manifestations such as hypotension or reduced haematocrit appear.

The use of ancillary drugs, such as anticholinesterases for neurotoxic envenoming, remains contentious.

If pulses are lost in a bitten limb, compartment syndrome should be suspected & surgical assessment requested.

Wound débridement& later skin grafting are occasionally required, especially in cobra & viper bites, but should never be carried out until the coagulation profile is normal.

Awareness &avoidance of the habitat of snakes are the major means of preventing snakebite.

SNAKE BITES

SNAKE BITES

SCORPION STINGS

The most important venomous animals after snakes. Most scorpion species produce a venom which causes only

minor local reactions in humans, but in Mexico, Tunisia, Algeria, Morocco, Libya scorpion stings are a serious health hazard.

Scorpions do not attack humans& escape when disturbed. Stings occur after a person accidentally steps on or

involuntarily presses the scorpion (when it is trapped inside shoes or clothes) or when reaching under dead wood or stones.

Clothes / shoes need to be inspected closely & shaken& sitting or sleeping places checked when camping in rural districts where scorpions are common

SCORPION STINGS

Two types of scorpion venom exist: 1.Venom of genera Hadrurus, Vejovis, Uroctonus only effects,

including sharp burning, swelling, discoloration,very rarely, anaphylaxis.

In envenoming by more poisonous species, Leiurus, common in the M. East, systematic manifestations develop, transfer to ICU required.

2. Venom, of genera of the poisonous varieties of Centruroides / Mesobuthus, contains neurotoxins block sodium channels& leads to spontaneous depolarisation of parasympathetic &sympathetic nerves results in tachycardia, hypertension, sweating, piloerection, hyperglycaemia & pulm oedema (esp Mesobuthus species)& seizures.

SCORPION STINGS

The sharp pain after a sting is quickly followed by paraesthesiae& numbness in the area due to peripheral nerve effects, muscle fasciculation& finally drowsiness.

With Centruroides& Mesobuthus there is no swelling at the sting site.

SCORPION STINGS: Management

Local pain & paraesthesiae are best treated with local compresses & oral analgesics.

Patients with significant envenoming should be hospitalised for at least 12 hours& observed for cardiovascular / neurological sequelae.

More severe symptoms may require airway support& 1-2 vials of IV antivenin.

The effectiveness of antivenin is controversial, but it is beneficial in the very young, the elderly or those with severe hypertension.

True anaphylaxis to antivenin occurs rarely. Serum sickness is common after antivenin but is usually self-

limiting & easily controlled with corticosteroids/histamines.


Tachyarrhythmias can be treated with IV metoprolol or esmolol.

Prazosin, an α-adrenoceptor antagonist, is indicated if hypertension or pulmonary oedema develops.

Prazosin also stimulates the secretion of insulin (which often falls during envenoming) & prevents hyperglycaemia.

Other treatments, as calcium or sympathomimetic drugs, are of little value.



Spidar venom:

All spiders produce venom and are capable of biting humans.

Although spider bites in general may be capable of producing allergic

systemic reactions, only the bite of the Widow Spiders and the Recluse

spiders produce serious wounds and may be be potentially life threatening.

Field Safety AwarenessInsects


The most important stinging insects include: Yellow Jackets Hornets Paper Wasps Bees Fire Ants Stinging caterpillars

Other stinging insects of lower threat potential include: Scorpions Centipedes Wheel bugs Solitary Wasps Mud dabbers Cicada killers

Field Safety AwarenessSocial Wasps

Social Wasps include Yellow Jackets Hornets Paper Wasps

All social wasps may sting repetitively!


[“Venomous Arthropods”, Public Health Pesticide Applicator Training Manual, University of Florida and American Mosquito Control Association, at http://vector.ifas.ufl.edu/ and

“Forest Pests of North America: A Guide For Foresters in the South”, Terry S. Price, University of Georgia, Warnell School of Forest Resources at http://www.forestpests.org/publichealth/ ]

Field Safety AwarenessSocial Bees

Social bees include:

European and Africanized Honey Bees

Bumble Bees

Carpenter bees

Honey Bee, A. Burns Weathersby, The University of Georgia,

0001011, at http://www.insectimages.org/browse

/detail.cfm?imgnum=0001011, University of Georgia Insect Images.

Bumble Bee, :Harry Pratt, Centers for Disease Control and Prevention, 0001014 at http://www.insectimages.org/browse/detail

.cfm?imgnum=0001014, University of Georgia Insect Images.

Carpenter Bee, Carl Dennis, Auburn University, at http://

www.insectimages.org/browse/detail.cfm?imgnum=1203155, University of Georgia Insect Images

Honey Bees in a hollow pine tree, Georgia Forestry Commission Archives, Georgia Forestry Commission, 0001007, University of Georgia Insect Images.

Bees sting only once! Once is enough.

http://vector.ifas.ufl.edu/




Field Safety AwarenessFire Ants

Fire ant stings appear initially as a red wheal

attended by severe burning and itching. The

wheal progresses to a clear blister, then to a

cloudy necrotic pustule. Breaking the pustule

offers the opportunity for secondary

infection.

Multiple Fire Ant Stings, Murray S. Blum, The University of Georgia, 0001006, University of Georgia Insect Images.

Single Early Fire An,t Sting, Jerry A. Payne, USDA ARS, 0001001, University of Georgia Insect Images.

Fire ant stings should always be washed with soap and water and treated with antihistamine and antibiotic creams to prevent itching & infection.




Field Safety AwarenessStinging Caterpillars

Puss Caterpillar, Lacy L. Hyche, Auburn University, 1430162, University of Georgia Insect Images.

Saddleback Caterpillar, Clemson University - USDA Cooperative Extension Slide Series, 1233068, University of Georgia Insect Images.

Io Moth Caterpillar, Clemson University - USDA Cooperative Extension Slide Series, 1233031, University of Georgia Insect Images.

White Marked Tussock Moth Caterpillar, John H. Ghent, USDA Forest Service, 0488007, University of Georgia Insect Images.

Hag Moth Caterpillar, Jerry A. Payne, USDA ARS, 0001030, University of Georgia Insect Images.

Spiny Oak Slug, Jerry A. Payne, USDA ARS, 1227101, University of Georgia Insect Images.

Key Point Review

Stinging insects include bees, wasps, hornets, yellow jackets, fire ants,

and stinging caterpillars. These stinging insects are present in areas where division officers must work on a regular basis.

Stinging insects may be debilitating if multiple stings are received, or severe allergic and/or other systemic reactions may occur. Allergic reactions to insect stings may be fatal.

Bee’s leave stingers in the wound. The stingers must be removed immediately to prevent additional venom from being pumped into the wound. Wasps, fire ants and caterpillars may sting repeatedly.

Bee and wasp venom contains chemicals that cause strong allergic reactions and histamine production in the wound area. Fire ant toxin produces less histamine but greater necrotic effects.

Key Point Review

A poultice or wet table salt applied to a bee or wasp sting is effective in

preventing inflammation. Multiple stings should receive an application

of wet table salt and immediate medical attention.

All sting victims should be watched closely for signs of allergic and/or

other systemic reactions. Obtain immediate medical assistance if systemic effects are noted.

Biting flies include mosquitoes, tabanid flies and biting midges.

Mosquitoes are ubiquitous & are implicated in the vectortransmission of Eastern Equine Encephalitis, St. Louis Encephalitis,

West Nile Virus and other diseases between animals and man.

Key Point Review

Tabanid flies are blood-sucking nuisance insects that are also capable of

transmitting diseases. The bites are painful and produce strong itching.

Tabanid flies breed in moist soils with high organic contents. They include horse flies, deer flies, yellow flies, stable flies and similar insects. They are sometime so numerous that extraordinary physical protection is required to work in areas infested with tabanid flies.

Wash tabanid fly bites with soap and water. Treat with anti-itch creams.

Use insect repellants that contain DEET (N, N diethyl-m-toluamide) Tabanid flies are sometimes so numerous that extraordinary protective measures such as the use of “bee-keeper” netting, gloves w/taped sleeves, and pants tucked into boots are required to accomplish any effective work.

Key Point Review

Biting midges are also known as “no-see-ums” or “sand gnats”. They are

very small biting flies that breed in damp soils with lots of organic

matter.

Biting midges are often so numerous they can literally cover skin surfaces!

The most effective biting midge bite prevention is effective clothing;

long sleeves, pants legs, head gear, even gloves. Use of an insect repellant containing DEET is also necessary, but physical barriers

are the most effective deterrent.

Health & Medicine

Medicine 5th year, 11th lecture (Dr. Mohammad Shaikhani)