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Insect stings and envenomation

ISSN 2398-2950

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Introduction

  • Venoms are poisonous substances that certain animals can inject by means of a bite, sting or other sharp body feature.
  • Many animals can be described as venomous; these include a wide range of invertebrates and certain fish and reptiles.
  • Amongst the invertebrates, we find spiders, centipedes, scorpions and a wide range of stinging insects. This article deals specifically with venomous insects and focuses particularly on the Hymenoptera.
  • The Hymenoptera, or wasp, order is a very large order containing the sawflies and a wide range of parasitic insects as well as the bees, wasps, hornets and ants. Most bees and wasps are solitary insects, each living and fending for itself. Ants, bumble bees, honey bees and some wasps are social insects, however. As such, they live in colonies ruled by one or more large female queens, and all work together for the good of the colony.
  • In the UK, the common wasp (Vespula vulgaris) and the honey bee (Apis mellifera) are almost certainly the most common insects likely to sting companion animals. Ants may also bite (or sting) pets.
  • In the southeastern United States, the most common culprit responsible for insect stings is probably the Imported Fire Ant (Solenopsis invicta).
  • Many caterpillars also have defensive venom glands, These are associated with specialized bristles, known as urticating hairs.
    Print off the owner factsheet Insect stings  Insect stings   to give to your client.

Presenting signs

  • Restlessness, pain, swelling, redness, pruritus, localized irritation.
  • Dyspnea and dysphagia may accompany stings to the face, mouth and oropharynx.
  • In cases of anaphylaxis, bronchospasm, pulmonary edema, hemorrhage, laryngeal edema, as well as ptyalism, pruritus, vomiting, incoordination, coma and death may all be seen.

Acute presentation

  • In cases of anaphylaxis Anaphylaxis, bronchospasm, pulmonary edema, hemorrhage, laryngeal edema, as well as ptyalism, pruritus, vomiting, incoordination, coma and death may all be seen.

Geographic incidence

  • Bees and their cousins, the bumblebees, wasps, hornets and ants are found throughout the United Kingdom.
  • They are usually not active at temperatures below 13° C (55° F) or on rainy days. The highest incidence of stings is therefore typically in August.
  • The spread of processionary caterpillars across Western Europe has increased the incidence of reactions to their urticating hairs.

Breed/Species predisposition

  • Inquisitive breeds and individuals may investigate, and/or catch, insects and may perhaps be more predisposed to being stung.

Public health considerations

  • Public health considerations are minimal. Where a bee or wasp nest is found and disturbed within the home and garden there may be some risk to humans, particularly if hypersensitized individuals are exposed.

Cost considerations

  • Minimal.

Special risks

  • Oropharyngeal edema, where present, may compromise respiration and make intubation difficult.
  • Urticating hairs of the Oak Processionary caterpillar (Thaumetopoea processionea) and Pine Processionary caterpillar (Thaumetopoea pityocampa) can cause intense swelling of the tongue and oral tissues if licked from the hair coat. This can lead to severe tissue damage and necrosis of the lingual tissues.

Pathogenesis

Etiology

  • Bees and their cousins, the bumblebees, wasps, hornets and ants, do not usually sting unless stepped on, touched, or molested.
  • The poison gland system of the bee consists of a small alkaline gland and a larger acid gland. In the bee the venom is produced by these two glands, which are associated with the ovipositor (egg-laying organ) of the female. The stinger is made up of two lancets with sharp barbs pointing backward, similar to a harpoon. This distinction is important for it means that the sting of a bee will usually remain implanted in the skin of the individual that has been stung. In doing so, it will tear away from the bees abdomen, leading to the death of the bee. The stinger left behind by the bee can continue to inject venom into the tissues.
  • Wasps and hornets, by contrast, have smooth stingers and are therefore able to retain their stingers.
  • The Imported Fire Ant can be very aggressive if their nest is disturbed (Wojciket al, 2001).

Predisposing factors

General

  • Contact with bees, wasps and other stinging insects.

Specific

  • Insects are attracted to flower fragrances, bright colors against dark backgrounds as well as sugary foods.
  • Bees and wasps tend to frequent clover fields, orchards, picnic sites and dustbins.
  • Certain insects, including the Imported Fire Ant, are aggressive if their nest is disturbed.
  • Urticarial caterpillars may be encountered when holidaying in continental Europe.

Pathophysiology

  • Bee venom is a very complicated substance with several active bio chemical components.
  • At least eight active components plus several biological inactive components have been identified. The substances showing activity are histamine, melittin (a protein), a hyaluronidase, and phospholipase A.
  • The histamine is not thought to be a pharmacological factor in bee venom. Histamine can, however, be released in allergic individuals in response to the sting.
  • The protein, Melittin, is thought to be responsible for the general local toxicity of the venom and, at high concentrations, can cause hemolysis of red blood cells.
  • Bee venom contains at least two enzymes, including a hyaluronidase and phospholipase A. Hyaluronidase facilitates venom infiltration through the tissues. Phospholipase A causes inactivation of thrombokinase, inhibits oxidative phosphorylation, and attacks enzymes involved with metabolic dehydrogenation. The pain experienced after being stung may well be the result of these last three actions.
  • Wasp venom also contains the enzymes hyaluronidase and phospholipase A.
  • Sensitization to insect venom can occur after a single sting.
  • The most allergenic component of wasp venom is a protein called Antigen 5 (or Ves g V). The most allergenic component of bee venom is the enzyme phospholipase. The hyaluronidase enzymes present in both bee and wasp venom may result in cross reaction allergy but the incidence of this in dogs is uncertain.
  • The bulk of Imported Fire Ant venom consists of piperidine alkaloids. These are present in a non-protein, non-polar alkaline phase. The alkaloids are cytotoxic and are responsible for the severe inflammatory response.

Timecourse

  • Non allergic reactions may develop over a period of up to several hours and resolve over the following few days.
  • Allergic reactions in sensitized individuals may develop within 10 minutes of a sting.

Diagnosis

Presenting problems

  • Pain, redness and swelling will usually accompany a sting. This is a manifestation of a local toxic reaction to the venom.
  • Dyspnea and dysphagia may accompany stings to the face, mouth and oropharynx.
  • Anaphylaxis may be seen in sensitized individuals:
    • Wasp and bee stings are responsible for the majority of naturally occurring cases of anaphylactic reactions in animals.
    • Clinical signs differ between dogs and cats.

Client history

  • The animal may have been observed chasing or playing with a bee or wasp.
  • The animal may have been seen to ingest the insect.
  • The animal may have come into contact with other known venomous insects.

Clinical signs

  • Pain, redness and swelling will usually accompany a sting.
  • Dysphagia and dyspnea may accompany stings to the face, mouth and oropharynx.
  • Clinical signs of anaphylaxis may include bronchospasm, pulmonary edema, hemorrhage, laryngeal edema, as well as ptyalism, vomiting, incoordination, coma and death.

Diagnostic investigation

  • A careful examination of the patient is required to establish the number and location of any stings.
  • Any animal having received stings to the face and throat should be examined for signs of swelling, dyspnea and dysphagia and kept under close observation.

Confirmation of diagnosis

Discriminatory diagnostic features

  • History of contact with a stinging insect.

Definitive diagnostic features

  • None specifically.

Gross autopsy findings

  • Localized swelling may be seen at the sting site.
  • Lung edema, hemorrhage and tracheal collapse Trachea: collapse may be seen in severe cases.
  • Dark kidneys and hemorrhagic diathesis have also been reported.

Histopathology findings

  • Skeletal muscle necrosis and acute renal tubular necrosis are the major histological changes reported in humans. They have also been reported in dogs (Shimadaet al, 2005).
  • Hepatocellular necrosis, myocardial necrosis and respiratory damage may also occur.

Differential diagnosis

  • Differential diagnoses for acute facial swelling (+/- urticaria) include acetaminophen toxicity, anterior caval syndrome, lymphadentitis, vasculitis Cutaneous vasculitis, hypoalbuminemia Hypoproteinemia and contact dermatitis Skin: irritant contact dermatitis.
  • Differential diagnoses for analphylactic shock include any cause of vomiting and diarrhea, toxin exposure, internal hemorrhage, congestive heart failure Heart: congestive heart failure, lower airway disease and upper airway obstruction.

Treatment

Initial symptomatic treatment

  • The treatment of bee stings should prioritize the following:
    • The speedy (ideally immediate) removal of the sting.
    • The application of ice to reduce any swelling.
    • The application of meat tenderizer where available.
  • The bee 'stinger' contains venom that can continue to be injected into the skin. In human patients it is suggested that a credit card or similar edge be dragged across the skin to remove the 'stinger' and prevent further release of venom. Whilst it is probably true that tweezers should not be used to remove the stinger because of the risk that they can express venom into the skin, the rapidity of the removal of the stinger is now emphasized over the method used. In animal patients this act is made a little more difficult by the dense hair coat that can obscure the stinger. The use of a credit card can still be recommended: the edge of the card should be drawn across the affected area. In competent hands it may be appropriate to use a razor blade, or a pair of fine scissors, to shave through the fur and cut the 'stinger' at skin level.
  • The use of meat tenderizer is now a standard recommendation in human medicine as it contains papain, which breaks down the various portein components of bee venom.
  • Where none of the above options are helping or available, use of a mild alkali can be recommended. Within the average household, the most dependable source of alkali will be toothpaste, which often contains bicarbonate. Small amounts of this should be applied over the sting. Bicarbonate of soda will also be available as baking soda; this can be diluted and applied to the affected area. Calamine lotion is another commonly available mild alkali that can be recommended.
  • Wasp stings do not require removal from the skin. Ice should be applied to the area to reduce any swelling. Papain (meat tenderizer) is again recommended for the treatment of such stings. Wasp stings have a pH of 6.8-6.9 and are therefore neutral rather than alkaline in pH. The application of vinegar to wasp stings is therefore likely to have limited benefit(s) if any.
  • Formic acid, produced by ants, has a pH of 2-3 and is therefore markedly acidic, making the use of neutralizing alkali appropriate.

Standard treatment

  • Pain relief may be indicated.
  • An animal presenting in analphylactic shock should have a secure airway established. This may require endotracheal intubation Endotracheal intubation or an emergency tracheostomy Tracheostomy, temporary tracheostomy.
  • Intravascular access should be established to allow the administration of drugs and fluids as required.
  • Epinephrine Epinephrine should be administered at 0.01 ml/kg IV (1:1000 epinephrine).
  • Intravenous crystalloid fluids should be provided at approximately one quarter of a calculated shock dose (90 ml/kg/h in dogs, 44 ml/kg/h in cats).
  • A short-acting corticosteroid should be administered (dexamethasone sodium phosphate 0.25 -1.0 mg/kg IV Dexamethasone).

Monitoring

  • Where local signs of envenomation are present the owner should be instructed to observe the patient at home.
  • Where envenomation has resulted in anaphylactic shock, the patient should be hospitalized until complete resolution of clinical signs.
  • Intravenous fluid therapy should be continued until the patient is no longer hypotensive and vomiting and diarrhea have resolved.

Subsequent management

Treatment

  • Intravenous fluid therapy should be continued until the patient is no longer hypotenisve and vomiting and diarrhea have resolved.
  • Blood pressure monitoring is indicated to monitor the anaphylactic patient with hypotension.

Monitoring

  • No specific long term monitoring indicated unless consideration to be given to desensitization.

Prevention

Control

  • Wasp and bee nests should be avoided.

Prophylaxis

  • It may be advisable to supply allergic individuals with an Epipen.
  • Venom desensitization immunotherapy is used to desensitize at-risk human patients.

Outcomes

Prognosis

  • Localized envenomation carries a good prognosis.
  • Anaphylactic reactions require prompt emergency treatment.

Expected response to treatment

  • Generally good.

Reasons for treatment failure

  • Severe anaphylactic shock.
  • Severe envenomation the amount of venom may vary depending on the species of insect and number of stings.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Niza M E, Ferreira R L, Coimbra I V et al (2012) Effects of Pine Processionary Caterpillar Thaumetopoea pityocampa Contact in Dogs: 41 cases (2002-2006). Zoonoses and Public Health 59 (1), 35-38 PubMed
  • Shimada A, Nakai T, Morita T et al (2005) Systemic rhabdomyonecrosis and acute tubular necrosis in a dog associated with wasp stings. Vet Rec 156 (10), 320-322 PubMed.
  • Wojicek D P, Craig C R, Brenner R J et al (2001) Red Imported Fire Ants: Impact on biodiversity. American Entomologist 47 (1), 16-23 Oxford Academic.
  • Noble S J & Armstrong P J (1999) Bee sting envenomation resulting in secondary immune-mediated hemolytic anemia in two dogs. J Am Vet Med Assoc 214 (7), 1026-1027 PubMed.
  • Waddell L S & Drobatz K J (1999) Massive envenomation by Vespula spp. in two dogs. J Vet Emerg Crit Care (2),  67-71 VetMedResource.
  • Friberg C A & Lewis D T (1998) Insect hypersensitivity in small animals. Compend Contin Educ Pract Vet 20 (10), 1121-1131 VetMedResource.

Other sources of information

  • Cohen R (1995) Systemic anaphylaxis. In:Current Veterinary Therapy XII. Small Animal Practice.Ed: JBonagura. W B Saunders, Philadelphia, USA.

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