Snakes and scorpions may spring most readily to mind as a fearsome zoological hazard to travelers, but in practice, the dog bite is a much more common problem: in many countries, it carries a formidable risk of rabies, and in all cases requires prompt and careful management. Bathers and swimmers in the tropics should be aware of the various types of venomous marine animals, and individuals allergic to bee and wasp stings must also take special precautions.
Professor David A. Warrell has treated animal bites and stings in five continents. He is Professor of Tropical Medicine and Infectious Diseases at the University of Oxford, Honorary Clinical Director of the Alistair Reid Venom Research Unit at the Liverpool School of Tropical Medicine, and a Consultant to WHO.
Encounters with animals can produce the following medical problems, all of which are uncommon but potentially fatal: mechanical injury, poisoning, infection, infestation, and allergic reactions. Only the first three of these will be discussed in detail in this chapter.
Injuries: Attacks By Large Animals
A wide range of animals is equipped with claws, teeth, tusks, horns, or spines capable of inflicting serious mechanical injuries which may prove fatal. With the one exception of bites by domestic dogs, these accidents are very rare and are easily avoided by treating all large animals with respect and avoiding unnecessarily close contact with them.
Most wild animals, unless they are ill or starving, avoid confrontation with humans. Visitors to game parks in the tropics or to safari parks in the temperate zones should take local advice about where and when it is safe to walk. Strolls between dusk and dawn without a light invite attacks by large carnivores. It is usually safe to approach large carnivores in a hard-topped vehicle, but under some circumstances, this may not be a safe place from which to view elephants or rhinoceroses.
Animals in zoos or safari parks should not be assumed to be tamer and therefore safer. Three keepers have been killed by tigers and an elephant in a British safari park during the last few years, and in the last 15 years, tigers have killed 659 people in Sunder bans Reserve Forest, in West Bengal.
Other mammals are known to have killed or severely mauled humans include lions, tigers, leopards, wild cats, and hyenas’, bears, elephants, hippopotamuses, buffaloes, wolves, and wild pigs.
Sharks claim about fifty lives each year out of 100 reported attacks, mostly between latitudes 30°N and 30°S. Much smaller fish may pose a greater threat to human life in some parts of the world. Garfish, for example (which have long spear-like snouts), have been known to leap out of the water and impale fishermen in parts of the Indo-Pacific Ocean. Moray and conger eels, groupers, barracudas, and stingrays can also produce severe mechanical injuries with their teeth or spines.
It is foolhardy to wade, bathe, or swim in rivers or lakes in the tropics unless they are known to be safe—not only from bilharzia but from crocodiles as well. Crocodiles continue to take a small toll on human life. River in populations in the Sudan, Central Africa, and South-East Asia are at risk. The annual mortality from the Nile crocodile in Africa may exceed 1000 and small numbers of accidents caused by the salt-water or estuarine crocodiles continue to be reported from Indonesia, Sarawak, and Northern Australia.
The giant pythons (reticulated python of Indonesia, African rock python, and anaconda of South America) are certainly capable of killing a human and there are a few reliable reports of fatal attacks.
Travelers, however, are at far greater risk of receiving injury from a dog bite before leaving their home country than from a wild animal on their travels.
In the USA there are now more than a million dog bites each year requiring some sort of hospital attention; the number is increasing. In Liverpool and Sunderland, in the north of England, about 500 people per 100 000 population attend hospital each year because of dog bites. Reports of eleven deaths from dog bites were collected in a two-year period in the USA, and there have been several in the UK during the last few years. Domestic cattle (especially bulls), rams, pigs, cats, and even ferrets have also killed people.
Types of injury
Teeth and claws produce lacerating and destructive injuries to soft tissues. Tusks, horns, and antlers can tear and produce serious penetrating injuries resulting in blindness, pneumothorax, and haemothorax (leakage of air and blood into the lining of the lungs), perforation of the intestines, and bleeding from the liver and spleen. Even dog bites are capable of producing compound fractures (where the broken bone ends protrude through the skin).
All bites, goring’s, and mauling carry a heavy risk of infection with bacteria, viruses, and other micro-organisms present in the animal’s mouth or contaminating its claws, horns, etc. Large mammals may trample and kneel on the human victim, producing severe crush injuries.
A guide to the treatment of mammal bites, licks, and scratches is given in the Box on page 195. Mild superficial injuries should be cleaned thoroughly. Anyone who has suffered a serious attack should be taken to hospital for proper assessment. The use of antibiotics, anti-tetanus, and anti-rabies treatments may need to be considered.
Rabies or ‘hydrophobia’ is a virus infection of mammals that can be transmitted to humans in a variety of ways, but usually as the result of a bite by a domestic dog.
Rabies probably causes at least 50 000 human deaths each year, although only a small fraction of these are reported to official bodies such as the WHO. In areas where rabies exists, the infection is usually established and circulates only in a few particular animal species. These may include domestic animals, particularly dogs, and/or wild animal species, for example, skunks, raccoons, foxes, and insectivorous bats in North America; foxes in the Arctic; mongooses and vampire bats in the Caribbean;
vampire bats in Central and South America; foxes, wolves, raccoons dogs, and insectivorous bats in Europe; and wolves, jackals and small carnivores such as mongooses and civets throughout most of Africa and Asia.
Humans may contract rabies from any rabid animal, domestic or wild, but because of the particularly close association between humans and dogs the most common cause of human rabies worldwide is the bite of a rabid domestic dog (which may itself have contracted the virus from another dog, cat, or from a rabid wild animal). In some countries such as the USA, canine rabies has been largely eliminated through measures such as immunization, but there is still a risk to people who come in contact with rabies-affected wild animal populations—naturalists, animal trappers, and people on expeditions, for example. Thus a bite from a skunk in the mid-western USA or from a jackal in Africa could involve a very significant risk of rabies.
Rabies occurs in most parts of the world, in Greenland, Canada, and North America, throughout the USSR, China, and New Territories of Hong Kong, as well as in the main tropical regions.
The following areas are free of rabies at present: Britain and Ireland, Norway, Sweden and Iceland, Malaysia, New Guinea, Borneo, Taiwan, Japan, Oceania, Antarctica, Australia and New Zealand. Human and animal rabies is most common in parts of South America, the Indian subcontinent, Thailand, and the Philippines.
How infection occurs
Rabies infection can occur when the normal protective barrier provided by healthy, unbroken skin is breached by a bite or scratch, and the wound is contaminated with the animal’s saliva containing rabies virus. Rabies virus can penetrate unbroken mucous membranes such as those covering the eye and lining the mouth or nose. On a few occasions, rabies has developed after the virus had been inhaled—in the air of bat-infested caves—and as the result of a laboratory accident. On at least four occasions, recipients of corneal transplants from patients dying of unsuspected rabies have later developed rabies themselves.
After the virus has entered the body, one of three things may
Treatment of mammal bites, licks, and scratches First aid
- Scrub with soap or detergent and running water for at least five minutes.
- Remove foreign material (e.g. dirt, broken teeth).
- Rinse with plain water.
- Irrigate with a veridical agent, such as providing iodine, 0.01 per cent aqueous iodine, or 40-70 per cent alcohol (gin and whisky contain 40 per cent). Note: hydrogen peroxide, mercurochrome and quaternary ammonium compounds—the brightly colored antiseptic dyes still popular in some countries are not suitable for this purpose.
At the hospital or dispensary A medical attendant should:
- Check that first-aid measures (above) have been carried out.
- Explore and irrigate deep wounds (if necessary, under local or general anesthesia). Dead tissue should be cut away, but wound excision is rarely necessary.
- Avoid suturing (stitches) and occlusive dressings.
- Consider tetanus risk and treat accordingly:
[Booster dose of tetanus formal toxoid (0.5 ml by intramuscular injection) for those fully immunized in the past and boosted within the last ten years; human tetanus immunoglobulin (250 mg by intramuscular injection) for severe or grossly contaminated wounds that have been left untreated for more than four hours in a previously unimmunized person.]
Consider risk of infection with other bacteria, viruses, and fungi particularly associated with mammal bites. Preventive antibiotic treatment is advisable for severely contaminated wounds, e.g. a broad spectrum antibiotic such as cephalexin (500 mg four times a day for five days).
If the exposure occurred in a rabies-endemic area, consider post-exposure rabies vaccination.
Happen. The virus may be killed by antiseptics used to clean the wound or by the person’s own immune defense mechanisms. Unless this happens within a few days of the bite, the virus is likely to spread to the nerve endings in muscles and along the nerves which lead to the brain and spinal cord; it then multiplies and causes a severe infection of the central nervous system (called an encephalomyelitis) which is almost invariably fatal.
Rarely, it seems that the virus may become permanently or temporarily inactive after it has reached the nervous system; in the latter case the infection may flare up again, and progress months or even years after the initial bite, following some kind of stress. This may explain the occasional reports of very long incubation periods.
The incubation period the time interval between the bite and the first symptoms of rabies—is usually two to three months but can vary from a few days to many years. The earliest symptom of rabies infection of the central nervous system is itching, irritation, tingling, or pain at the site of the healed bite wound. The disease advances rapidly, producing headache, fever, spreading paralysis, and episodes of confusion, aggression, hallucination, and hydrophobia (literally fear of water). Attempts to drink water induce powerful contractions of the neck muscles and the muscles involved in swallowing and breathing in. These spasms are associated with indescribable terror. The patient dies in a few days.
Some species of animals such as mongooses, skunks, and vampire bats can recover from rabies encephalomyelitis, but in humans, the infection is almost invariably fatal. During the last fifteen years, two patients with probable rabies and only one with proven rabies have recovered after prolonged intensive care.
The prospect of an agonizing death from this untreatable disease should encourage everyone to do everything possible to prevent rabies.
Pre-exposure vaccination against rabies should be considered in the case of travelers who run a particularly high risk. These include cave explorers, animal collectors, zoologists, botanists, hunters, and also those whose work involves walking and cycling in urban or rural areas. One of the safe, new tissue culture vaccines should be used, such as the Institute Meraux human diploid cell strain vaccine (HDCSV) and purified Vero cell rabies vaccine (PVRV) or Behringwerke purified chicken embryo cell vaccine (PCEC) should be used (see Box, p. 198). The expense can be reduced by giving one-tenth of the normally recommended dose by intradermal rather than intramuscular or subcutaneous injection.
Travelers within a rabies endemic area should avoid close contact with domestic or wild mammals. They should be particularly wary of wild animals that appear tame, for this change in behavior is a common early sign of rabies in animals.
Action following a bite
Irrespective of the risk of rabies, all mammal bites, scratches, and licks on mucous membranes or broken skin should be cleaned immediately and vigorously (see Box, p. 195). Mammal bites (including human bites!) are usually contaminated by a variety of bacteria, some of which can cause serious infections.
In the case of deep penetrating or contaminated wounds, it is wise to take a prophylactic antibiotic (such as cephalexin 500 mg four times a day for five days—not to be taken by people with severe penicillin allergy). The risk of tetanus should always be considered: all travelers should be fully protected with a course of tetanus toxoid before starting their journey. An animal bite warrants a booster dose of tetanus toxoid (tetanus formal toxoid 0-5 ml) (see also p. 87).
The aim of post-exposure vaccination is to neutralize the rabies virus introduced by the bite before it can enter the nervous system. Treatment should be started as soon as possible, but although the chances of preventing rabies decrease with delay, vaccination is still worthwhile even weeks or months after the bite. The decision about vaccination should be made by a doctor, who will need the following information:
- When, where, and in which locality the bite occurred;
- The severity and site of the bite;
- The species, appearance, behavior, and fate of the biting animal, and whether it had been vaccinated against rabies during the last year.
The newer tissue culture ant rabies vaccines such as HDCSV carry no serious risk of reactions, unlike the older vaccines, which consisted of animal nervous tissue.
Passive immunization should never be omitted in cases of severe bites or high risk of exposure unless the patient has had the pre-exposure vaccination. ‘Ready-made’ rabies neutralizing antibody in the form of human rabies immunoglobulin (HRIG) or equine anti-rabies serum (EARS) is necessary to provide immediate activity against rabies virus during the interval of about seven days between vaccination and the first appearance of antibody produced by the body itself in response to the vaccine. HRIG is free from side-effects, but equine anti-rabies serum is complicated by allergic reactions such as serum sickness in up to 10 percent of those treated.
Travelers who are exposed to the risk of rabies (mammal bites, licks, scratches, etc.) should seek immediate help at the time of the incident, and not wait for days (or even months) until they return home before considering post-exposure treatment.
Only orthodox/Western medical practitioners should be consulted about rabies, not herbalists, homeopaths, traditional practitioners, monks, priests, or other practitioners of ‘fringe medicine’. In some countries, even Western-style practitioners may not give adequate treatment. No one exposed to rabies should allow themselves to be fobbed off with tablets or a single injection.
In the UK, expert advice and materials for post-exposure treatment is available from the Central Public Health Laboratory, Colindale (Tel. 01-205 7041), and in the USA, from local or state health departments, or from the Division of Viral Diseases at the Centers for Disease Control, Tel. (404) 329-3095 during working hours, (404) 329-3095 nights, weekends and holidays.
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