Infection and Disease

Measles

Measles is a viral disease which spreads by droplet infection. One attack confers a high degree of immunity. Most people suffer from measles in childhood, and a mother who has had the disease confers passive immunity on her infant for the first six months of life. The infection is generalized, but the clinical evidence is mainly found in the respiratory tract, the skin, the mouth and the conjunctivae. Measles is prevalent during the first six months of the year with a peak incidence in March. The disease is notifiable in England but not in Scotland. The incubation period is about 10 days to the commencement of the catarrhal stage. A quarantine period is not necessary.

Infection and Disease

Rubella (German Measles)

Rubella is a viral disease which spreads by droplet infection. One attack confers a high degree of immunity. The disease tends to affect older children, adolescents and young adults and it spreads less readily than measles. It occurs mainly in the spring and summer months. The disease in children is trivial. In adults the illness may be more severe, but of short duration and of little importance except when it develops in a woman during the first three to four months of pregnancy. In such cases the child may be born with a congenital malformation such as a cardiac or mental defect, cataract or deafness. The disease is not notifiable. The incubation period is usually about 18 days. A quarantine period is not necessary.

Infection and Disease

Mumps

Mumps is caused by a virus which spreads by droplet infection and affects mainly children of school age and young adults. The infectivity rate is not high and there is serological evidence that 30-40% of infections are clinically inapparent. Most cases occur in the spring. The incubation period is about 18 days. A quarantine period is not necessary: contacts should be watched for the first sign of disease from the 12^th to the 28^th day after exposure.

Infection and Disease

Chickenpox

Chickenpox is a viral infection which spreads by droplets from the upper respiratory tract or by contamination from the discharge from ruptured lesions of the skin or through contact with a patient with herpes zoster. Herpes zoster appears to be due to reactivation of a latent infection with chickenpox virus. It may be accompanied by a varicelliform rash. Chickenpox is highly infectious and chiefly affects children under 10 years of age. Most children are little incommoded by this disease but, as often happens with viral infections, adults may develop a more severe illness including a prodromal rash. A suspicion of smallpox may easily be aroused. Second attacks are very rare. In patients on long-term steroid therapy the disease may be severe or even fatal. Most recorded fatalities have been suffering from leukaemia and it is probable that blood disorder has been the major factor in reducing resistance to the virus. The disease is not notifiable. The incubation period is about a fortnight. A quarantine period is not necessary.

Infection and Disease

CHEMOTHERAPY OF INFECTIONS

The concept of chemotherapy is almost as old as the science of bacteriology. Attempts were made in the late nineteenth century to treat infections such as tuberculosis by the injection of other organisms or their products. The property of one micro-organism to interfere with the growth of another is called anti-biosis, this action being frequently due to specific diffusible metabolic products of bacteria and fungi; these substances were therefore called antibiotics. The first to be clinically effective was tyrothricin, a product of Bacillus brevis, and a mixture of gramicidin and tyrocidine. Unfortunately these antibiotics are relatively toxic to leucocytes and are of value only for topical application.

Infection and Disease

Erythromycin & The Cephalosporins

Erythromycin has a range of activity similar to benzylpenicillin but differs in being predominantly bacteriostatic. The main Indication for its use is in the treatment of streptococcal or pneumococcal infections in patients who are allergic to penicillin. Erythromycin is prescribed in a dosage of 250 mg by mouth every six hours. Jaundice occasionally occurs with erythromycin estolate but it clears on withdrawal of the antibiotic. Allergic reactions to erythromycin are rare but diarrhoea is not uncommon.

The Tetracyclines

Chlortetracycline, oxytetracycline and tetracycline. These are very closely related substances which, for practical purposes, have an identical and wide range of activity. This is offset to some extent by their action being bacterio-static and not bactericidal. The oral dose for an adult is 250-500 mg given at six-hourly intervals and taken before meals.

Chlortetracycline is used for the local treatment of skin infections as it does not cause cutaneous sensitization.

Demethylchlortetracycline and methacycline attain higher and more prolonged blood levels than the other tetracyclines and hence may be given less frequently.These advantages, however, are counter-balanced by the high degree of binding to plasma proteins.

PRINCIPAL INDICATIONS

The tetracyclines inhibit the growth of a wide range of Gram-positive and Gram-negative organisms and are particularly useful in the treatment of brucellosis and exacerbations of chronic bronchitis. Their value in chronic bronchitis has been limited recently by a significant increase in tetracycline-resistant pneumococci and to a lesser extent H. influenzae.

The tetracyclines are also active against the following organisms which are intermediate between bacteria and viruses:

(a) Rickettsia (typhus fevers)

(b) Coxiella burneti (Q-fever)

(c) Mycoplasma pneumoniae (atypical pneumonia)

(d) Chlamydiae (lymphogranuloma venereum, psittacosis).

The tetracyclines are also employed systemically in the treatment of acne vulgaris and rosacea where their beneficial effect is almost certainly not due only to their antibacterial action.

ADVERSE EFFECTS

Many of the normal saprophytes of the alimentary tract are sensitive to the tetracyclines and are inhibited when these antibiotics are administered. Insensitive organisms then multiply and cause ‘super-infection‘. This occurs particularly with fungi, such as Candida albicans, which cause stomatitis, glossitis, diarrhea or a distressing anal or vulvar pruritus. In hospital, superinfection with resistant staphylococci may occur and the ensuing enteritis, septicaemia or pneumonia can be fatal. Fortunately this is a rare complication of tetracycline therapy. Superinfection following the use of the tetracyclines emphasises that an antibiotic with a wide range of activity should not be prescribed if an appropriate ‘narrow-spectrum’ antibiotic is available. The tetracyclines quite commonly cause mild diarrhoea.

Pregnant women with pyelonephritis treated with tetracycline intravenously may develop severe liver damage. Staining of growing teeth and bone occurs and this could interfere with their growth and development in infants. Accordingly the use of tetracyclines is contraindicated in pregnancy and in childhood. The tetracyclines can also exacerbate renal failure and should not be given to patients with renal disease.