Chapter 27. Treatment of tropical and imported diseases; anthelmintics
At the end of this chapter, the reader should be able to:
• discuss the impact of modern air travel on the spread of tropical diseases
• describe the symptoms and treatment of tropical diseases that affect the gastrointestinal tract
• give an account of the cause and treatment of leprosy
• give an account of the cause, symptoms and use of drugs to suppress and treat malaria, and the limitations of treatment
• give an account of the protozoan infections such as leishmaniasis
• describe the treatments for the various worm infestations
• describe the precautions to take in order to reduce the chances of being bitten by flying insects, and provide sensible bite avoidance strategies
Introduction
Tropical diseases, like their background, are inclined to be dramatic and florid. The majority are infective or due to dietary deficiency, and in former times, and to some degree today, great epidemics have caused widespread disease with a very high death rate.
During the last 50 years, the causative organisms of nearly all these diseases have been discovered and drugs have been devised which are capable of dealing with them. The problem of treating tropical disease is further complicated by the primitive conditions which prevail in many parts of the tropics and the lack of proper medical and nursing facilities. However, in spite of these difficulties, immense progress has been made in this sphere.
In recent years, air travel has brought tropical diseases much nearer home (Ryan et al 2002). It is possible to catch malaria in Central Africa and not be taken ill until after arrival in London. Some knowledge of these disorders is therefore necessary even if the nurse does not intend to work in tropical countries. In this chapter, the consideration of tropical disease will be carried out under headings of the disease rather than the drug.
The diseases and infestations
Travellers’ diarrhoea
A holiday in tropical or subtropical countries is often interrupted by an attack of diarrhoea, colic and vomiting, which, although rarely severe, interferes with a few days’ pleasure. It is believed that there is usually an infective cause and the organism most often implicated is an unusual variant of Escherichia coli.
Prevention should include care over drinking water and washing uncooked foods such as fruit and vegetables in chlorinated water. The prophylactic use of antibiotics is not recommended except for those at special risk (e.g. bowel disease) or if for social or business reasons diarrhoea must be avoided. In these cases, trimethoprim or doxycycline is satisfactory. For the developed attack, fluid replacement with added glucose and electrolytes (e.g. Dioralyte or a similar preparation) is important. Symptoms can be improved with loperamide, which should not be given to children under 4 years. In severe cases, trimethoprim twice daily or ciprofloxacin as a single dose is effective.
Amoebic dysentery
Amoebic dysentery is an infection of the lower bowel by an organism called Entamoeba histolytica and is characterized by chronic diarrhoea. Sometimes the infection spreads outside the bowel, particularly to the liver, where it causes an abscess.
The chief drug used in this infection is metronidazole, which is now the first choice in treating amoebic infection of the bowel and abscess of the liver. (Metronidazole is also used to treat the protozoan parasite Trichomonas vaginalis.) A 5-day course is often sufficient. Vomiting can be troublesome at the dose levels used to treat amoebic dysentery.
Metronidazole can be combined with diloxanide furoate, which is active against organisms in the bowel lumen, but not in the tissues. The combination appears to be even more efficient at eradicating the infection.
Giardiasis
Giardiasis is due to the organism Giardia lamblia, which affects the intestine and causes distension, gas and frothy stools. Infection can occur in many parts of the world, and symptoms often develop on return from a holiday abroad. Metronidazole daily for 3 days is an effective treatment.
Bacillary dysentery
This may be caused by a variety of organisms of the Shigella group. In mild cases, symptomatic treatment only is required and there is no evidence that antibiotics produce a more rapid cure. In severe cases, the organism should be cultured and its sensitivity to antibiotics defined. If there is no time for culture, treatment may be started with trimethoprim twice daily. Ciprofloxacin is used if trimethoprim resistance is a problem. Fluid and electrolyte replacement is important.
Cholera
Cholera is due to an organism, Vibrio cholerae, which invades the intestine, producing severe and copious diarrhoea and vomiting. This leads to intense dehydration and sodium and potassium deficiency and is often fatal. The most important part of treatment is to replace the lost water and salts orally or by intravenous infusion.
The cholera vibrio is sensitive to tetracycline and ciprofloxacin, which can be used to eradicate the infection and shorten the course of the illness.
In developing countries, where this disease reaches epidemic proportions, large-scale intravenous infusion may be difficult. An important advance has been the discovery that if glucose is added to the electrolyte replacement solution and given orally, water and electrolytes are well absorbed and intravenous infusion is less often required. The oral replacement solution contains:
sodium chloride 3.5 g
sodium citrate 2.9 g
potassium chloride 1.5 g
glucose 20 g
made up to 1 litre.
The volume given is titrated against the loss in the stools and by vomiting. Some authorities claim that a most readily available and suitable alternative fluid in all countries, provided no other alternatives are available, is in the form of proprietary diet colas such as Coca-Cola or Pepsi-Cola. ( Tip: stay away from sugar when suffering from diarrhoea; sugar acts as a laxative.)
A cholera vaccine is available, but is of little use.
Leprosy
Leprosy is a disease of great antiquity and is referred to in the Bible. It is caused by the bacterium Mycobacterium leprae; these bacteria cause chronic infection of the skin, visceral nerves and other parts of the body. Leprosy has long resisted treatment, but in recent years the introduction of new drugs has made the outlook more hopeful.
Mycobacterium leprae can become resistant to the drugs used in treatment; therefore at least two antibacterial drugs should be given together to prevent this. Three drugs are used in leprosy at present: dapsone, clofazimine and rifampicin.
Dapsone is widely used. It is given orally, usually over long periods.
Adverse effects are uncommon, but include headaches, cyanosis, anaemia and blood dyscrasias.
Clofazimine is useful in treating leprosy and is combined with other agents. It is given orally over long periods.
Adverse effects are rare, but it may cause pigmentation of the skin.
Rifampicin is also effective against Mycobacterium leprae, although resistance may develop.
Malaria
Malaria has been known for thousands of years and is one of the most widespread diseases which attack humans. Although it is largely confined to tropical and subtropical zones, air travel has led to its increased frequency in this country. Malaria is most active in the broad band between the tropics. Increasing tourism to such areas has resulted in malaria presenting as a significant risk. Every year about 2000 travellers from the UK contract malaria and up to a dozen deaths occur as a result of infection. Over a third of such cases occur in those from ethnic groups resident in Britain who have returned to their country of origin for a visit.
Malaria is caused by a small organism called a plasmodium (Goodyer 2000b). There are three varieties of plasmodia which produce the commonly found varieties of human malaria. They are:
• Plasmodium vivax, which causes benign tertian malaria
• Plasmodium malariae, which causes quartan malaria
• Plasmodium falciparum, which causes malignant tertian malaria.
These plasmodia are injected into the bloodstream of the human victim by the mosquito. They are carried to the liver, where they go through a stage of division known as the exo-erythrocyte stage. After a short period, some plasmodia enter the red cells of the bloodstream. Here they divide in a simple asexual fashion to form more plasmodia, which rupture the red cells and then re-enter further red cells: the breaking up of the red cells corresponds with the rise of temperature with rigor and later sweating which is so characteristic of the disease.
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