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ABC of Safety in the Biological Sciences
ALLERGY
An allergy is an abnormal and individual hypersensitivity to any substance that is ordinarily harmless and is acquired by exposure to that particular allergen.33
Many substances used in the histopathology laboratory are potential allergens (see Allergen, this section). If an allergic reaction develops the allergen needs to be identified so that, if necessary, the particular person can avoid or modify their use of the material. It may become necessary to remove an affected person entirely from an area where a particular allergen causes them concern.
Allergy related disorders encountered in laboratory personnel include the following:
Eczema (contact dermatitis)
Contact dermatitis may be caused by primary
contact with an allergen or there may be a delayed hypersensitivity.
The allergens concerned are usually highly reactive chemical
compounds capable of combining with proteins and also dissolving in
lipids thus allowing for penetration of the dermis. Some reactions
occur from repeated contact with a substance over many months.
Direct irritants may damage normal skin or irritate an existing
dermatitis. Weak or marginal irritants such as soap, acetone or even
water may take several days of exposure to cause clinically
recognisable changes, whereas strong irritants may cause observable
changes within a few minutes. Contact dermatitis ranges from
transient redness to severe swelling and bulbar formation. Itching
and vesiculation are common. Medical attention is generally
required.
Asthma
The allergen induces constriction of the
smooth muscle in the small bronchi and increased mucus secretion in
the airways. This leads to airways obstruction and respiratory
distress. The affected person should be removed from the source of
the allergen, rested and kept warm. Medical advice should be
obtained. Treatment with a bronchodilator may be required.
Conjunctivitis and rhinitis
Conjunctivitis requires medical attention and
isolation from the allergen. Rhinitis is often only of temporary
inconvenience and usually resolves after removal from exposure.
Anaphylaxis
Cutaneous reaction
Anaphylaxis in the skin is characterised by
the eruption of well circumscribed wheals with erythematous, raised
edges and blanched centres. The lesions are pruritic and may occur
anywhere on the body where contact is made with the allergen. The
lesions reach maximum intensity in 15 to 20 minutes then slowly
subside over the next 48 hours, but in some forms may become
chronic.
Systemic reaction
An anaphylactic shock may occur in any
individual who has a predisposition to an IgE mediated
hypersensitivity reaction resulting from exposure to an allergen.
Smooth muscle contraction is prominent with a fall in body
temperature, hypotension, bradycardia and decreased serum complement
levels. Circulatory shock with dizziness and faintness may be the
only signs of the reaction but collapse, unconsciousness and death
can occur. The most common causes of systemic reactions are
injection of drugs such as penicillin, or the more natural
occurrence of a bee sting. If systemic shock occurs the individual
requires rest and warmth. Always get medical attention.
Arthus reaction
This response is indicated by an inflammatory
necrotic lesion marked by oedema and haemorrhage at the site of
injection of a soluble antigen to which the individual is sensitised.
Lesions are not limited to skin but may occur in any vascular organ
such as stomach, liver, kidney, brain and joints. The lesions
generally reach maximum intensity in 2 to 5 hours and may take
several days to resolve. Medical advice should be obtained if an
Arthus reaction is suspected.
Anaemia
Antigens may attach to cell membranes and
function as haptens. The red cell hapten complex may induce an
immune response in which the antibody reacts with the allergen on
the cell surface causing lysis through activation of complement.
This haemolytic reaction is normally drug-induced but can also be
caused by many laboratory chemicals. Affected persons should seek
immediate medical attention.
Lymphadenopathy
Swelling of lymph nodes may occur in allergic
response. The onset of swelling is usually rapid and can last for
several days during which time the lesions can often be painful. The
lymph nodes most commonly involved are those found in the neck but
other areas of the body may also be affected.
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