Environmental health risks

Travellers often experience abrupt and dramatic changes in environmental conditions, which may have detrimental effects on health and well-being. Travel may involve major changes in altitude, temperature and humidity, and exposure to microbes, animals and insects. The negative impact of sudden changes in the environment can be minimized by taking simple precautions. 3.1 Altitude Barometric pressure falls with increasing altitude, diminishing the partial pressure of oxygen and causing hypoxia. The partial pressure of oxygen at 2500 m, the altitude of Vail, Colorado, for example, is 26% lower than at sea level; in La Paz, Plurinational State of Bolivia (4000 m), it is 41% lower. This places a substantial stress on the body, which requires at least a few days to acclimatize; the extent of acclimatization may be limited by certain medical conditions, especially lung disease. An increase in alveolar oxygen through increased ventilation is the key to acclimatization; this process starts at 1500 m. Despite successful acclimatization, aerobic exertion remains difficult and travellers may still experience problems with sleep. High-altitude illness (HAI) results when hypoxic stress outstrips acclimatization. HAI can occur at any altitude above 2100 m but is particularly common above 2750 m. In Colorado ski resorts, incidence of HAI varies from 15% to 40%, depending on sleeping altitude. Susceptibility is primarily genetic, but fast rates of ascent and higher sleeping altitudes are important precipitating factors. Age, sex and physical fitness have little influence. The spectrum of HAI includes common acute mountain sickness (AMS), occasional high-altitude pulmonary oedema and, rarely, high altitude cerebral oedema. The latter two conditions, although uncommon, are potentially fatal. AMS may occur after 1–12 h at high altitude. Headache is followed by anorexia, nausea, insomnia, fatigue and lassitude. Symptoms usually resolve spontaneously in 24–48 h and are ameliorated by oxygen or analgesics and antiemetics. Acetazolamide, 5 mg/kg 33 Chapter 3. Environmental health risks per day in divided doses, is an effective chemoprophylaxis for all HAI; it is started one day before travel to altitude and continued for the first 2 days at altitude. Acetazolamide should not be given to individuals with history of allergy to sulfonamide drugs. Only a few conditions are contraindications for travel to altitude; they include unstable angina, pulmonary hypertension, severe chronic obstructive pulmonary disease (COPD) and sickle-cell anaemia. Patients with stable coronary disease, hypertension, diabetes, asthma or mild COPD and pregnant women generally tolerate altitude well but may require monitoring of their condition. Portable and stationary oxygen supplies are readily available in most high-altitude resorts and – by removing hypoxic stress – remove any potential danger from altitude exposure. Precautions for travellers unaccustomed to high altitudes ● Avoid one-day travel to sleeping altitudes over 2750 m if possible. Break the journey for at least one night at 2000–2500 m to help prevent AMS. ● Avoid overexertion and alcohol for the first 24 h at altitude; drink extra water. ● If direct travel to sleeping altitude over 2750 m is unavoidable, consider prophylaxis with acetazolamide. Acetazolamide is also effective if started early in the course of AMS. ● Travellers planning to climb or trek at high altitude will require a period of gradual acclimatization. ● Travellers with pre-existing cardiovascular or pulmonary disease should seek medical advice before travelling to high altitudes. ● Travellers with the following symptoms should seek medical attention when experiencing, at altitude: — symptoms of AMS that are severe or last longer than 2 days; — progressive shortness of breath with cough and fatigue; — ataxia or altered mental status. 3.2 Heat and humidity Sudden changes in temperature and humidity may have adverse effects on health. Exposure to high temperature results in loss of water and electrolytes (salts) and may lead to heat exhaustion and heat stroke. In hot dry conditions, dehydration is particularly likely to develop unless care is taken to maintain adequate fluid intake. The addition of a little table salt to food or drink (unless this is contraindicated International Travel and Health 2012 34 for the individual) can help to prevent heat exhaustion, particularly during the period of adaptation. Consumption of salt-containing food and drink helps to replenish the electrolytes in case of heat exhaustion and after excessive sweating. Travellers should drink enough fluid to be able to maintain usual urine production; older travellers should take particular care to consume extra fluids in hot conditions, as the thirst reflex diminishes with age. Care should be taken to ensure that infants and young children drink enough liquid to avoid dehydration. Irritation of the skin may be experienced in hot conditions (prickly heat). Fungal skin infections such as tinea pedis (athlete’s foot) are often aggravated by heat and humidity. A daily shower using soap, wearing loose cotton clothing and applying talcum powder to sensitive skin areas help to reduce the development or spread of these infections. Exposure to hot, dry, dusty air may lead to irritation and infection of the eyes and respiratory tract. Avoid contact lenses in order to reduce the risk of eye problems. 3.3 Ultraviolet radiation from the sun The ultraviolet (UV) radiation from the sun includes UVA (wavelength 315– 400 nm) and UVB (280–315 nm) radiation, both of which are damaging to human skin and eyes. The intensity of UV radiation is indicated by the Global Solar UV Index, which is a measure of skin-damaging radiation. The Index describes the level of solar UV radiation at the Earth’s surface. The values of the Index range from zero upwards, the higher the Index value, the greater the potential for damage to the skin and eyes and the less time it takes for harm to occur. Index values are grouped into exposure categories, with values greater than 10 being “extreme”. In general, the closer to the equator the higher is the Index. UVB radiation is particularly intense in summer and in the 4-h period around solar noon. UV radiation penetrates clear water to a depth of 1 m or more. UV radiation increases approximately 5% for every 300 m altitude gain. The adverse effects of UV radiation from the sun are the following: ● Exposure to UV radiation, particularly UVB, can produce severe debilitating sunburn, particularly in light-skinned people. ● Exposure of the eyes may result in acute keratitis (“snow blindness”), and long-term damage leads to the development of cataracts. 35 Chapter 3. Environmental health risks ● Exposure to sunlight may result in solar urticaria – a form of hives associated with itching and redness on areas of skin exposed to sunlight. It can occur within minutes of exposure to the sun and is usually short-lasting. ● Long-term adverse effects on the skin include: — the development of skin cancers (carcinomas and malignant melanoma), due mainly to UVB radiation; — accelerated ageing of the skin, due mainly to UVA radiation, which penetrates more deeply into the skin than UVB. ● Adverse reactions of the skin result from interaction with a wide range of medicinal drugs that may cause photosensitization and result in phototoxic or photoallergic dermatitis. Various types of therapeutic drugs such as antimicrobials as well as oral contraceptives and some prophylactic antimalarial drugs may cause adverse dermatological reactions on exposure to sunlight. Phototoxic contact reactions are caused by topical application of products, including perfumes, containing oil of bergamot or other citrus oils. ● Exposure may suppress the immune system, increasing the risk of infectious disease, and limiting the efficacy of vaccinations. Precautions ● Avoid exposure to the sun in the middle of the day, when the UV intensity is greatest. ● Wear clothing that covers arms and legs (covering the skin with clothing is more effective against UV than applying a sunscreen). ● Wear UV-protective sunglasses of wrap-around design plus a wide-brimmed sun hat. ● Apply a broad-spectrum sunscreen of sun protection factor (SPF) 15+ liberally on areas of the body not protected by clothing and reapply frequently. ● Take particular care to ensure that babies and children are well protected. ● Avoid exposure to the sun during pregnancy. ● Take precautions against excessive exposure while on or in water or on snow. ● Check that medication being taken will not affect sensitivity to UV radiation. ● If adverse skin reactions have occurred previously, avoid any exposure to the sun and avoid any products that have previously caused the adverse reactions. International Travel and Health 2012 36 3.4 Foodborne and waterborne health risks Many important infectious diseases (such as campylobacteriosis, cholera, cryptosporidiosis, cyclosporiasis, giardiasis, hepatitis A and E, listeriosis, salmonellosis, shigellosis and typhoid fever) are transmitted by contaminated food and water. Information on these and other specific infectious diseases of interest for travellers is provided in Chapters 5 and 6. 3.5 Travellers’ diarrhoea Travellers’ diarrhoea is a clinical syndrome associated with contaminated food or water that occurs during or shortly after travel. It is the most common health problem encountered by travellers and, depending on length of stay, may affect up to 80% of travellers to high-risk destinations. Travellers’ diarrhoea most commonly affects individuals travelling from an area of more highly developed standards of hygiene and sanitation to a less developed one. Diarrhoea may be accompanied by nausea, vomiting, abdominal cramps and fever. Various bacteria, viruses and parasites are the known causes of travellers’ diarrhoea, but bacteria are responsible for the majority of cases. The safety of food, drink and drinking-water depends mainly on the standards of hygiene applied locally in their growing, preparation and handling. In countries or areas with low standards of hygiene and sanitation and poor infrastructure for controlling the safety of food, drink and drinking-water, there is a high risk of contracting travellers’ diarrhoea. To minimize any risk of contracting foodborne or waterborne infections in such countries, travellers should take precautions with all food and drink, even that served in good quality hotels and restaurants. While the risks are greater in poor countries, locations with poor hygiene may be present in any country. Another potential source of waterborne infection is contaminated recreational water (see next section). It is particularly important that people in more vulnerable groups, i.e. infants and children, the elderly, pregnant women and people with impaired immune systems, take stringent precautions to avoid contaminated food and drink and unsafe recreational waters. Treatment of diarrhoea Most diarrhoeal episodes are self-limiting, with recovery in a few days. It is important, especially for children, to avoid becoming dehydrated. When diarrhoea starts, fluid intake should be maintained with safe liquids (e.g. bottled, 37 Chapter 3. Environmental health risks boiled or otherwise disinfected water). Breastfeeding should not be interrupted. If moderate to heavy diarrhoeal losses continue, oral rehydration salt (ORS) solution should be considered, in particular for children and elderly individuals. Amounts of ORS solution to drink Children under 2 years 1 /4–1 /2 cup (50–100 ml) after each loose stool up to approximately 0.5 litre a day. Children 2–9 years 1 /2–1 cup (100–200 ml) after each loose stool up to approximately 1 litre a day. Patients of 10 years or older As much as wanted, up to approximately 2 litres a day. If ORS solution is not available, a substitute containing 6 level teaspoons of sugar plus 1 level teaspoon of salt in 1 litre (approximately 1 quart) of safe drinkingwater may be used, in the same amounts as for ORS. (A level teaspoon contains a volume of 5 ml.) Antibiotics such as fluoroquinolones (e.g. ciprofloxacin or levofloxacin) may be used as empirical therapy in most parts of the world and usually limit the duration of illness to an average of about one day. However, increasing resistance to fluoroquinolones, especially among Campylobacter isolates, may lower their efficacy in some parts of the world, particularly in Asia. In such cases, azithromycin may be taken as an alternative treatment. Azithromycin is a first-line antibiotic therapy for children and pregnant women. When travellers need immediate control of symptoms, antidiarrhoeal drugs such as loperamide may be additionally used, but such antimotility drugs are contraindicated in children aged less than 3 years and not recommended for children under the age of 12. Prophylactic use of antibiotics is controversial. There is a role for their use in travellers with increased susceptibility to infection, e.g. people with hypochlorhydria or small intestinal pathology and individuals on critical missions. Antidiarrhoeal medicines such as loperamide are always contraindicated for prophylactic use. Medical help should be sought if diarrhoea results in severe dehydration or has not responded to empirical therapy within 3 days and particularly when bowel movements are very frequent and watery, or when there is blood in the stools, repeated vomiting or fever. In the event of distressing symptoms suggesting a diagnosis other than travellers’ diarrhoea, medical advice should be sought rapidly. International Travel and Health 2012 38 3.6 Recreational waters The use of coastal waters and freshwater lakes and rivers for recreational purposes has a beneficial effect on health through exercise, and rest and relaxation. However, various hazards to health may also be associated with recreational waters. The main risks are the following: ● Drowning and injury (Chapter 4). ● Physiological: — chilling, leading to coma and death; — thermal shock, leading to cramps and cardiac arrest; — acute exposure to heat and UV radiation in sunlight: heat exhaustion, sunburn, sunstroke; — cumulative exposure to sun (skin cancers, cataract). ● Infection: — ingestion or inhalation of, or contact with, pathogenic bacteria, fungi, parasites and viruses; — bites by mosquitoes and other insect vectors of infectious diseases. ● Poisoning and toxicoses: — ingestion or inhalation of, or contact with, chemically contaminated water, including oil slicks; — stings or bites of venomous animals; — ingestion or inhalation of, or contact with, blooms of toxigenic plankton. 3.6.1 Exposure to cold: immersion hypothermia Cold, rather than simple drowning, is the main cause of death following immersion. When the body temperature falls (hypothermia), there is confusion followed by loss of consciousness, so that the head goes under water leading to drowning. With a life jacket capable of keeping the individual’s head out of water, drowning is avoided, but death due directly to hypothermic cardiac arrest will soon follow. However, wearing warm clothing as well as a life jacket can greatly prolong survival in cold water. Children, particularly boys, have less fat than adults and chill very rapidly in cool or cold water. Swimming is difficult in very cold water (5 °C or below), and even good swimmers can drown suddenly if they attempt to swim even short distances in water at these temperatures without a life jacket. Life jackets or some other form of flotation aid should always be worn in small craft. 39 Chapter 3. Environmental health risks Alcohol, even in small amounts, can cause hypoglycaemia if consumed without food and after exercise. It causes confusion and disorientation and also, in cold surroundings, a rapid fall in body temperature. Unless sufficient food is eaten at the same time, small amounts of alcohol can be exceedingly dangerous on long-distance swims, as well as after rowing or other strenuous and prolonged water-sports exercise. Those engaging in winter activities on water, such as skating and fishing, should be aware that whole-body immersion must be avoided. Accidental immersion in water at or close to freezing temperatures is extremely dangerous: the median lethal immersion time (time to death) is less than 30 min for children and most adults. Immediate treatment is much more important than any later action in reviving victims of immersion hypothermia. A hot bath (the temperature no higher than the immersed hand will tolerate) is the most effective measure. In case of drowning, cardiac arrest and cessation of breathing should be treated by giving immediate external cardiac massage and artificial ventilation. Cardiac massage should not be applied unless the heart has stopped. People who have inhaled water should always be sent to hospital to check for pulmonary complications. 3.6.2 Infection In coastal waters, infection may result from ingestion or inhalation of, or contact with, pathogenic microorganisms, which may be naturally present, carried by people or animals using the water, or present as a result of faecal contamination. The most common consequences among travellers are diarrhoeal disease, acute febrile respiratory disease and ear infections. Skin abrasions from corals are frequently contaminated by live coral organisms and severe skin infections can ensue quickly. In fresh waters, leptospirosis may be spread by the urine of infected rodents, causing human infection through contact with broken skin or mucous membranes. In areas endemic for schistosomiasis, infection may be acquired by penetration of the skin by larvae during swimming or wading (Chapter 5). In swimming pools and spas, infection may occur if treatment and disinfection of the water are inadequate. Diarrhoea, gastroenteritis and throat infections may result from contact with contaminated water. Appropriate use of chlorine and other disinfectants controls most viruses and bacteria in water. However, the parasites Giardia and Cryptosporidium, which are shed in large numbers by infected individuals, are highly resistant to routine disinfection procedures; they are inactivated by ozone or eliminated by filtration. International Travel and Health 2012 40 Contamination of spas and whirlpools may lead to infection by Legionella and Pseudomonas aeruginosa. Otitis externa and infections of the urinary tract, respiratory tract, wounds and cornea have also been linked to spas. Direct person-to-person contact or physical contact with contaminated surfaces in the vicinity of pools and spas may spread the viruses that cause molluscum contagiosum and cutaneous papillomas (warts); fungal infections of the hair, fingernails and skin, notably tinea pedis (athlete’s foot), are spread in a similar manner. 3.6.3 Precautions ● Adopt safe behaviour in all recreational waters (Chapter 4). ● Comply with posted rules and regulations. ● Avoid consumption of alcohol before and during any activities in or near recreational waters. ● Provide constant supervision of children in the vicinity of recreational waters. ● Avoid temperature extremes in spas, saunas, etc; this is particularly important for users with pre-existing medical conditions, pregnant women and young children. ● Avoid contact with contaminated waters and unclean sand or soil. ● Apply antiseptic to coral cuts and abrasions. ● Avoid swallowing any water. ● Obtain advice locally about the presence of potentially dangerous aquatic animals. ● Wear shoes when walking on shores, riverbanks and muddy terrain. 3.7 Animals and insects 3.7.1 Mammals Undomesticated animals tend to avoid contact with humans and most do not attack unless provoked. Some large carnivores, however, are aggressive and may attack. Animals suffering from rabies often become aggressive and may attack without provocation. Wild animals may become aggressive if there is territorial intrusion, particularly when they are protecting their young. Animal bites may cause serious injury and may also result in transmission of disease. 41 Chapter 3. Environmental health risks Rabies is the most important infectious health hazard from animal bites. In many developing countries, rabies is transmitted mainly by dogs, but many other mammalian species can be infected by the rabies virus. After any animal bite, the wound should be thoroughly cleansed with disinfectant or with soap or detergent and water, and medical or veterinary advice should be sought about the possibility of rabies in the area. Where a significant risk of rabies exists, the patient should be treated with post-exposure rabies vaccination and immunoglobulin (Chapter 5). A booster dose of tetanus toxoid is also recommended following an animal bite. Travellers who may be at increased risk of exposure to rabies may be advised to have pre-exposure vaccination before departure (Chapter 6). Pre-exposure rabies vaccination does not eliminate the need for treatment after the bite of a rabid animal, but it reduces the number of vaccine doses required in the post-exposure regimen. Precautions ● Avoid direct contact with domestic animals in areas where rabies occurs, and with all wild and captive animals. ● Avoid behaviour that may startle, frighten or threaten an animal. ● Ensure that children do not approach, touch or otherwise provoke any animal. ● Treat any animal bite immediately by washing with clean water, disinfectant or soap and seek medical advice. ● If a significant risk of exposure to rabies is foreseen, seek medical advice before travelling. Travellers with accompanying animals should be aware that dogs (and, for some countries, cats) must be vaccinated against rabies in order to be allowed to cross international borders. A number of rabies-free countries have additional requirements. Before taking an animal abroad, the traveller should ascertain the regulatory requirements of the countries of destination and transit. 3.7.2 Snakes, scorpions and spiders Travellers to tropical, subtropical and desert areas should be aware of the possible presence of venomous snakes, scorpions and spiders. Local advice should be sought about risks in the areas to be visited. Most venomous species are particularly active at night. Venom from snake and spider bites and from scorpion stings has various effects International Travel and Health 2012 42 in addition to tissue damage in the vicinity of the bite. Neurotoxins are present in the venom of both terrestrial and aquatic snakes, and also often in the venom of scorpions and spiders. Neurotoxins cause weakness and paralysis. Venom contacting the eyes causes severe damage and may result in blindness. Most snake venoms affect blood coagulation, which may result in haemorrhage and reduced blood pressure. Toxins in the hair of spiders such as tarantulas may cause intense irritation on contact with the skin. Poisoning by a venomous snake, scorpion or spider is a medical emergency requiring immediate attention. The patient should be moved to the nearest medical facility as quickly as possible. First-aid measures involve immobilizing the entire affected limb with splints and firm, but not tight, bandaging to limit the spread of toxin in the body and the amount of local tissue damage. However, bandaging is not recommended if local swelling and tissue damage are present in the vicinity of the bite. Other traditional first-aid measures (incisions and suction, tourniquets and compression) are harmful and should not be used. The decision to use antivenom should be taken only by qualified medical personnel. Antivenom should be administered in a medical facility and should be given only if its stated range of specificity includes the species responsible for the bite. Precautions ● Obtain local advice about the possible presence of venomous snakes, scorpions and spiders in the area. ● Avoid walking barefoot or in open sandals in terrain where venomous snakes, scorpions or spiders may be present; wear boots or closed shoes and long trousers. ● Avoid placing hands or feet where snakes, spiders or scorpions may be hiding. ● Be particularly careful outdoors at night. ● Examine clothing and shoes before use for hidden snakes, scorpions or spiders. Sleep under a mosquito net. 3.7.3 Aquatic animals Swimmers and divers may be bitten by certain aquatic animals, including conger and moray eels, piranhas, seals and sharks. They may be stung by venomous cnidaria jellyfish, fire corals, sea anemones, stingrays, weever fish, scorpionfish, stonefish and invertebrate aquatic species. Severe and often fatal injury results from 43 Chapter 3. Environmental health risks attack by crocodiles, which inhabit rivers and estuaries in many tropical countries, including the tropical north of Australia. Injuries from dangerous aquatic organisms occur as a result of: — being in contact with a venomous organism while bathing or wading; — treading on an animal with venomous spines; — handling venomous organisms during sea-shore exploration; — invading the territory of large animals when swimming or at the water’s edge; — swimming in waters used as hunting grounds by large predators; — interfering with, or provoking, dangerous aquatic organisms. Precautions ● Obtain local advice on the possible presence of dangerous aquatic animals in the area. ● Avoid behaviour that will provoke attack by predatory animals. ● Wear shoes or sandals when walking on the shore and at the water’s edge. ● Avoid contact with jellyfish (both live jellyfish in water and dead jellyfish on the beach). ● Avoid walking, wading or swimming in crocodile-infested waters at all times of year. ● Seek medical advice after a sting or bite by a venomous animal. Treatment Treatment of envenomation by aquatic animals will depend on whether there is a wound or puncture or a localized skin reaction (e.g. rash). Punctures caused by spiny fish require immersion in hot water, extraction of the spines, careful cleaning of the wound and antibiotic therapy (and antivenom in the case of stonefish). If punctures were caused by an octopus or sea urchin the treatment is basically the same but without exposure to heat. In the case of rashes or linear lesions, contact with cnidaria should be suspected; the treatment is based on the use of 5% acetic acid, local decontamination and corticosteroids (antivenom for the box jellyfish Chironex fleckeri), with adequate follow-up for possible sequelae. 3.7.4 Insects and other vectors of disease International Travel and Health 2012 44 Vectors play an essential role in the transmission of many infectious diseases. Many vectors are bloodsucking insects, which ingest the disease-producing microorganism during a blood meal from an infected host (human or animal) and later inject it into a new host at the time of another blood meal. Mosquitoes are important insect vectors of disease, and some diseases are transmitted by bloodsucking flies. In addition, ticks and certain aquatic snails are involved in the life cycle and transmission of disease. The principal vectors and the main diseases they transmit are shown in Table 3.1. Information about the diseases and details of specific preventive measures are provided in Chapters 5, 6 and 7. Water plays a key role in the life-cycle of most vectors. Thus, the transmission of many vector-borne diseases is seasonal as there is a relationship between rainfall and the existence of breeding sites. Temperature is also a critical factor, limiting the distribution of vectors by altitude and latitude. Travellers are usually at lower risk of exposure to vector-borne diseases in urban centres, especially if they sleep in air-conditioned rooms. They may, however, be exposed to the vectors of dengue which are frequent in urban centres in tropical countries and which bite mostly during the day. Travellers to rural areas or to areas with low standards of hygiene and sanitation are usually at higher risk of exposure to disease vectors, and personal protection is therefore essential. Evening/nighttime activities outdoors may increase exposure to malaria vectors. Protection against vectors Travellers may protect themselves from mosquitoes and other vectors by the means outlined in the following paragraphs. Insect repellents are substances applied to exposed skin or to clothing to prevent human/vector contact. The active ingredient in a repellent repels insects but does not kill them. Choose a repellent containing DEET (N,N-diethyl-3-methylbenzamide), IR3535 (3-[N-acetyl-N-butyl]-aminopropionic acid ethyl ester) or Icaridin (1-piperidinecarboxylic acid, 2-(2-hydroxyethyl)-1-methylpropylester). Insect repellents should be applied to provide protection at times when insects are biting. Care must be taken to avoid contact with mucous membranes; insect repellents should not be sprayed on the face, applied to the eyelids or lips, or applied to sensitive, sunburned or damaged skin or deep skin folds. Always wash the hands after applying the repellent. Repeated applications may be required every 3–4 h, especially in hot and humid climates when sweating may be profuse. When the product is applied to clothes, the repellent effect lasts longer. However, label instructions should be followed to avoid damage to certain fabrics. Repellents 45 Ch