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SERUM REACTIONS
This page based on the article of Atwell and Campbell:
Atwell RB and Campbell FE (2001) Reactions to tick antitoxin serum and the role of atropine in treatment of dogs and cats with tick paralysis caused by Ixodes holocyclus: a pilot survey; Aust Vet J 79(6), June 2001.
The study was conducted Dec 1999 to Jan 2000 as a retrospective mailed-out questionnaire to veterinarians in paralysis tick endemic areas (90 forms returned).
Reported incidence of Tick Antiserum reactions
| dogs | cats | |
|---|---|---|
| Cases reported in study | 14,550 | 6,054 |
| All types of serum reactions (%) | 3.3 | 6.2 |
| Bezold-Jarisch reflex type (%) | 2.7 | 3.9 |
| Anaphylactic type (%) | 0.6 | 2.3 |
| Incidence of B-J type when pretreated with atropine | 0.5 | 0.9 |
The dose of atropine may be important in preventing the B-J reflex. The normal anaesthetic-premedication dose of atropine is 0.04 mg/kg, which is significantly lower than the 0.1-0.2 mg/kg recommended for prevention of the B-J reflex.
Characterisation of Tick Antiserum reactions
| B-J Reflex | Anaphylaxis | |
|---|---|---|
| Pathophysiologic Effects | Chemical stimulation of cardiac receptors in the posterior wall of the left ventricle initiates a vagally mediated cholinergic response (bradycardia)* | Foreign antigens act on mast cells and basophils to cause cellular degranulation and release of endogenous chemicals that affect multiple organ systems |
| Physiologic responses | Bradycardia; systemic vasodilation; reduced total peripheral resistance, and slight, though insignificant [sic], reduction in myocardial contractility | peripheral vasodilation; increased vascular permeability; constriction of smooth muscle of bronchi, gastrointestinal tract and coronary artery; pulmonary vasoconstriction and increased production of airway mucus |
| Clinical signs | Bradycardia; pale mucous membranes; hypotension; weakness; depression; reduced heart sounds | Tachycardia; injected mucous membranes; anxiety or restlessness; piloerection on the back of the neck; swelling of the lips; cutaneous wheals; erythema; diarrhoea; vomiting; coughing; dyspnoea |
| Treatment | atropine 0.1-0.2 mg/kg IV |
adrenaline using 1:1000 solution- |
*The vagal reflex induces bradycardia while hypotension results from a combination of sympathetic withdrawal and cholinergic vasodilation. The minor negative inotropic component is solely dependent on the negative chronotropic response. If untreated, persistent bradycardia and hypotension, together with poor ventricular function, will lead to a further decline in cardiac output and and systemic arterial pressure, with subsequent induction of circulatory shock.
The Bezold-Jarisch reflex is primarily a parasympathetic (cholinergic) overstimulation, and much less importantly a sympathetic (adrenergic) understimulation (withdrawal). Thus, giving adrenaline (an adrenergic) is of minimal benefit in the B-J reflex. Atropine, on the other hand (an anticholinergic) is very beneficial.
Conversely, in anaphylactic reactions atropine is of little benefit but adrenaline is highly useful.
Conclusion
With such a large proportion of adverse reactions to tick antiserum administration ascribable to the B-J reflex, the routine use of atropine as a premedication in tick paralysis cases may substantially reduce the number of adverse clinical reactions to tick antiserum.
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