other diseases

Although Malaria is the main worry for the traveller a number of other airborne disease risks are of concern. Some tropical diseases can also be contracted from the environment and these should also be considered by travellers.
You often hear of horror stories concerning tropical diseases but  many of the diseases described in this article are more relevant to the local population and to expatriate or other workers living in the area than to tourists on short holidays. However, travellers on trips of longer duration may be at increased risk. Non-specific symptoms after travel to the tropics can be caused by a number of tropical diseases and referral to a general practitioner, and possibly a specialist centre is advisable.
As it is virtually impossible to diagnose many of these tropical diseases in their early stages, malaria should be presumed in the first instance, particularly if there is fever.

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The arboviruses

Dengue fever  "breakbone fever"

Dengue fever  is becoming increasingly common in tropical and subtropical climates being a particular problem in Asia and parts of South America, affecting an estimated 50 million people each year.It also occurs in African countries such as Mauritania around to Nigeria, with patches around the Egypt and the Sudan border. In Asia DF is endemic in Pakistan, Southern China and through to the North West area of Australia. 

Since there is no vaccine it is important that preventitive measures to avoid getting bitten by the responsible mosquito Aedes aegypti are taken. It is worth remembering that this mosquito is a daytime feeding species.The affected individual may experience fevers, malaise, headaches, joint and muscle pain which in some cases can be quite severe.
The incubation period is usually one week but can range  between two to 14 days and the first symptom is fever, which may subside after the initial bout to recur some days later. Around the third to fifth day, a  rash can appear on the trunk, spreading to the limbs and face. After the sixth day, the fever subsides, but convalescence can take several weeks. Only partial immunity to dengue is gained and reinfection can occur.
A potentially fatal  reaction called dengue haemorrhagic fever (DHF), can occur, usually in children under the age of 15. In this form, the immune system causes damage to blood vessels and plasma leakage  resulting in dengue shock syndrome. The mechanism probably involves the formation of virus/antibody complexes . DHF is more likely to occur in children who have previously experienced dengue fever. There may also be an increased risk of DHF among those formerly resident in endemic areas who are returning for a visit.
Dengue fever  often coexists with malaria from which, in the early stages, it is hard to distinguish.  
Dengue fever is probably greatly under-reported because, in many cases, the fever is relatively mild and causes minor symptoms. A risk assessment of around one illness per 1,000 travellers to some areas has been suggested.
For adult travellers there is little, if any, risk of the more severe DHF. In addition, children travelling to endemic areas would be at little risk if they have not previously been exposed to dengue. For most people, the fever will subside in a week, but a longer convalescence period may well ruin a short holiday.
There is no specific treatment for dengue. Management of the fever is usually with  paracetamol rather than aspirin because of additional risk of DHF. Oral rehydration such as Dioralyte,Electrolade may also be advisable where there has been excessive sweating and/or diarrhoea. Malaria and dengue often coexist in the same area, so it is advisable to assume in the first instance that any fever contracted in such areas is due to malaria.

Yellow fever

Like dengue, yellow fever can be transmitted by A aegypti and is caused by the same group of flaviviruses. Unlike dengue, yellow fever is a zoonosis, ie, the disease can be harboured by animal vectors. It is an extremely serious infection and mortality can be between 20 to 50 per cent.

Yellow fever infected areas
These are areas where the virus is present in monkeys and is a potential risk to humans as defined by the World Health Organisation. The mosquitoes capable of transmitting the disease are present in various non-endemic countries..
Some of these countries demand a yellow fever certificate from travellers as a condition of entry to their country. Many of these, and other countries, will ask you for a certificate if you are entering from an infected country.  
Your travel agent should inform you if you need a certificate when you are booking your holiday or flight. It is only available from specified local yellow fever vaccination centres. (details from your local Health Authority). The vaccine is a single dose which is effective after ten days. Period of protection is 10 years

Yellow fever is endemic in many tropical areas of South America and Africa, but is absent in Asia. The majority of cases are reported in Africa and it is estimated that there are as many as 200,000 cases world-wide per year.

The disease gains its name from the damage caused to the liver which results in jaundice. Other complications contributing to the high death rate are kidney  heart damage, severe bleeding  and shock.

The severe bleeding can be confused with ebola as the following story from Germany illustrates.
A German photographer returned from a trip to the Ivory Coast in 1999, with symptoms of what appeared to be Ebola virus infection. This sparked off a tremendous scare, with fears of an ebola outbreak in Europe. A perimeter fence was erected around the patient's isolation unit, with security guards patrolling. All his contacts on the aeroplane were traced and his colleagues and family placed in quarantine. He eventually died and the disease was confirmed as yellow fever and not Ebola as first thought. Apparently he had never been vaccinated and had somehow managed to gain entry into the country without a certificate. This shows the importance of being vaccinated against yellow fever if it is indicated, whether or not a vaccination certificate is required for entry into the country.
Yellow fever is mainly encountered by the few non vaccinated tourists but due to the certificate requirements very rarely by most travellers.

Japanese encephalitis

Japanese encephalitis (JE) is also caused by a flavivirus. It is endemic in many parts of Asia and the west Pacific. It is spread by the Culex mosquito which tends to breed in rice paddies.
It is a zoonosis capable of being carried by birds, although the most important reservoir is domestic pigs. Occasionally, epidemics arise which result in the culling of the pig population.
The clinical picture of infection includes a sudden onset of fever, with headaches and vomiting. If JE results, there are neurological disturbances which may prove fatal or result in permanent disability. However, only around one in 200 people infected by the virus will progress to develop encephalitis. Children, in particular, are at most risk and form the majority of the fatalities during an epidemic.
The most important consideration for travellers is whether or not it is worth obtaining vaccination when visiting potentially endemic areas. As the outbreaks tend to occur during the monsoon season when mosquitoes are more plentiful, vaccination may be advisable for those travelling on extended visits to rural areas at such times. Reports of JE among travellers are quite rare; in the US, only 11 cases have been reported since 1981 and an attack rate of one case per 10,000 people per week was estimated for military personnel stationed in Asia.

Some other arboviruses

The other arboviruses listed in Table 1 have all reached media attention over the past few years. A common feature of these arboviruses is that they are all mosquito-borne and have a bird or other animal as a host. Such reports will often unjustifiably deter travel to the affected areas. Different insects can transmit arboviruses. A good example is tick borne encephalitis, which is found not in the tropics but in parts of Scandinavia, east Europe and Russia. It is a particular risk to people rambling in the forested parts of these areas.

Filarial diseases

Elephantiasis (lymphatic filariasis)  is caused by a filarial worm (Wuchereria bancrofti) carried by mosquitoes. It invades the lymphatic system, resulting in localised inflammation of the lymph glands. Heavy levels of this  parasite  may on occasions block lymphatic drainage and cause greatly enlarged limbs or scrotum. It would be unusual for travellers to pick up enough worms to do any harm, although some individuals may develop allergic reactions to the worms.

Onchocerciasis A similar situation to elephantitis applies to onchocerciasis or river blindness. While this is an important cause of blindness to the local population in parts of Africa, it rarely causes problems to travellers. There are cases of expatriates or people working on projects in endemic areas needing treatment. It is treated with ivermectin, which stops the reproduction of the worms but must be taken yearly for several years.

Loiasis(african eye worm) rarely affects travellers but is one of the most strange filarial diseases. The person affected  might notice a slight blurring of the vision in one eye, and on looking in the mirror will be horrified to observe a worm a few centimetres long wriggling just underneath the conjunctiva. Although it can be removed under a local anaesthetic, the worm is best left as it will leave the conjunctiva in under an hour, rarely doing any harm.

Protozoal diseases

As with many of the arbovirus infections, protozoal diseases are comparatively rare in travellers, being of more concern to the local population.

Leishmaniasis

Leishmaniasis is caused by a small protozoan organism that is transmitted by the bite of a sandfly. It is found in areas of North Africa and some areas of Central Africa ,Middle East, South America ,South East Asia and the Southern Mediterranean. Travellers to some tourist areas of the Mediterranean are at potential, if extremely small, risk of the disease. It is often not recognised by physicians unused to seeing the condition. There are rarely more than 20 cases per year reported in travellers from the UK and just 129 cases were reported in travellers from the US between 1978 and 1990.
The parasite is a zoonosis, being carried by both domestic and wild animals. Bite avoidance is the only method of protection. It was of particular concern among servicemen fighting in the Gulf war, and was the reason why repellents and insecticides of various types were so widely used.
The parasite will invade macrophages and the organism can then potentially be carried around the body. This results in so-called visceral leishmaniasis, or Kala-Azar, caused by L donovani. The symptoms include an enlarged spleen and lymph glands. This form is potentially fatal unless treated with somewhat toxic drugs, such as pentavalent antimony (sodium stibogluconate).
Other species of leishmania will cause a local reaction at the site of a sandfly bite. This is cutaneous leishmaniasis. The lesion will initially appear as a nodule, which eventually developes into a disfiguring chronic ulcer.Prevention is avoiding movement outside at dawn and dusk.Sleeping in high places such as on roofs where the sandfly cannot jump ,and under treated mosquito nets.

Trypanosomiasis

 African trypanosomiasis or "sleeping sickness" is transmitted by bite of the Tsetse fly and is due to either T brucei gambiense or T brucei rhodesiense. The latter is usually directly transmitted from animals to man and the former from man to man. After the bite of a Tsetse fly, which is notoriously painful, the tryptosomal chancre will appear after about five days as a raised inflamed area which can increase in size over a couple of weeks. Travellers should not confuse this with the initial reaction to the bite, which is seen very soon after being bitten. There may be a fever, headaches and enlarged lymph gland. These early signs of the disease can be intermittent, lasting many months, and may be accompanied by anaemia and skin rashes. During early stages of the disease, an acute, rapidly fatal toxaemia can develop. This is more common with T rhodesiense. It can be up to two years before central nervous sysytem (CNS) involvement occurs, with psychoactive disturbances and long sleeping periods (from which the disease derives its name).
The disease has a patchy distribution over much of sub-Saharan Africa, with travellers on safari being at greatest risk. The message for the traveller is to watch out for a tryptosomal chancre and any non-specific symptoms because the disease can be treated with suramin in its early stages.
Very few travellers from the UK contract the disease and it would normally be treated before there is any CNS involvement. In Germany, just 11 cases have been reported in travellers since 1970 and, from the US, only 14 since 1967.
In some parts of South America, another form of trypanosomal infection called Chagas' disease is endemic. This is transmitted by a species of cone-nosed bug, sometimes called the assassin bug, which lives in the walls of dwellings in the more rural areas. Infection can cause chronic renal and gastrointestinal damage. Travellers would be advised not to sleep in the mud (adobe) huts that are common in parts of South and Central America.

Some other diseases caused by insects

Typhus

Typhus is caused by bacteria-like micro-organisms called Rickettsiae and infection results in skin rashes, fevers and spleen enlargement. It can be transmitted by flea bites from either humans (R prowazekii) or animals (R mooseri) and can present a potential hazard to those working in refugee camps in Africa.
Of a much wider distribution is the form of typhus spread by tick (R tsutsugamushi) or mite bites. Forms of scrub typhus transmitted by ticks are found in parts of the south African veld and in North America, where it is known as Rocky Mountain Spotted Fever. A scrub typhus transmitted by mites is present in the tropical bush of south east Asia and the Pacific Islands.

Tick-borne infections

 It is not only the tropics that can harbour tick-borne infections. Ticks from deer can transmit Lyme disease, a bacterial infection due to Borrelia burgdorferi that can cause chronic joint, cardiovascular and CNS complications. Lyme disease is quite widely distributed round the world, including Europe; at present, it has a low incidence in the UK. In the US, it is probably the most common vector-borne disease. It is worth removing ticks as quickly as possible, without damaging the tick in the process and causing it to release more bacteria into the wound. This is best achieved by gripping the tick with tweezers, pushing down to disengage the teeth, while gently rocking it from side to side before pulling away.

Plague

Plague transmitted by fleas is endemic in some parts of the world, including areas of North America where it is harboured by some wild animals and is occasionally contracted by humans. Elsewhere, for instance in parts of sub-Saharan Africa, local epidemics of plague occur periodically. A small epidemic of plague hit India in 1994, severely affecting the tourist industry. A vaccine is available, but is rarely used except by those planning to work in areas where plague is endemic. Oxytetracycline can be effective to treat plague if used in the early stages. Travel need not be deterred, although travellers should be warned that contact with animals, particularly rodents, should certainly be avoided. During the plague scare in India, no travellers contracted the disease.

Skin conditions The most graphic of all conditions caused by insects is myiasis, ie, maggots developing in human skin. The flies responsible are the Tambu and Bot flies of tropical Africa. Tambu flies lay their eggs on clothing hung out to dry and the resulting small larvae are able to penetrate the skin when they hatch. Travellers should be advised to iron clothing left out in this way to destroy any eggs. Placing raw bacon over the maggots' breathing hole is a recognised method of removing them.

Tropical diseases of contact

Schistosomiasis

There are some tropical diseases that can be contracted by methods other than insect vectors which may be of concern to travellers. Chief among these is schistosomiasis, also known as bilharzia.
Schistosomiasis is an infection caused by small fluke like worms that rely upon fresh water snails as part of their life cycle. Eggs from the worm are passed into fresh water by the urine of infected individuals. In the fresh water, they develop into larvae that enter the snails. These larvae then multiply within the snails and are released as free swimming circaedia, which can penetrate the skin of human bathers. Eventually, the mature worms will find their way to the bladder (S haematobium) or the intestine (S mansoni and S japonicum). The worms will then lay their eggs in the veins of these organs causing localised inflammation and tissue damage. This leads to bleeding and, if not treated, a chronic anaemia.
Bathers may notice an irritation of the skin after emerging from contaminated water and a few may experience a fever. Otherwise, it can be months or even years before symptoms become apparent. Schistosomiasis is widespread in Africa and is also present in some parts of South America and Asia. A particular problem has been identified in recent years around Lake Malawi (in Africa) and a number of British tourists have been found to be infested after bathing in the lake. There were 133 cases reported to the Communicable Diseases Review in 1998; cases were more likely in those individuals on lengthy stays.
Tourists in Africa should be particularly warned against bathing in fresh water. If contact with such water occurs, it would be best to rub down with a towel after bathing rather than letting the water dry off in the sun. It may be worthwhile for some travellers who have had a lot of contact with potentially contaminated water to be tested for the disease. Treatment with praziquantel is very effective.

Leptospirosis

 Another disease of potential danger to the traveller, particularly to those trekking in the wild, is leptospirosis or Weil's disease. The urine of rodents or other animals passes the disease into surface waters. The leptospira enters humans through small breaks in the skin or mucus membranes and causes a severe febrile illness. There may be complications involving liver or renal damage and the disease has a fatality rate as high as 30 per cent. It can be a particular problem in areas of flooding, for instance, following the recent hurricane Mitch. Generally, trekkers should be advised to minimise direct contact with fresh water.

Hantavirus

A further reason for travellers to avoid any contact with environments infested with rodents is the possibility of Hantavirus infection, which can cause haemorrhagic, pulmonary or renal complications. A pulmonary form has been identified in the US which causes occasional fatalities.

Creeping eruption and other worm infestations

 Hook worms, which are usually seen as parasites of dogs, can sometimes cause problems in humans. This arises when larvae are picked up through the skin, usually as a result of walking barefoot, perhaps when walking along a beach. The worms essentially become "lost" in an unfamiliar host and will move around beneath the surface of the skin producing an elongated inflamed line on the soles of the feet. This gives the condition the name of creeping eruption or Larva Migrans. It is common on the beaches of Africa and south east Asia, but can occur in other parts of the world, including the US.
Travellers should therefore be warned against walking barefoot along beeches above the high water line. Treatment is with thiabendazole which can be taken orally or formulated as a 1 per cent paste in white soft paraffin for local application.
Other worm infestations of the gut, eg, ascariasis and tape worm, can occur as a result of eating poorly prepared food.
Another worm, which is of particular curiosity to the traveller, is the Guinea worm or dracunculosis. This can be contracted by drinking contaminated water from wells in some parts of the world. The worm will find its way to the skin where it protrudes to release its larvae. Soon after, the worm will die, and has to be removed by gently wrapping it around a matchstick over a period of some weeks. Dracunculosis can potentially result in infected ulcers. Worms up to 100cm in length have been recorded. There has been a fairly successful worldwide campaign of eradication, so it is extremely rare in travellers.

Lassa, Marburg and Ebola virus

These viruses are sometimes the source of great panic and give rise to media headlines of "body melting diseases". They are zoonotic viruses that can attack a variety of tissues in the body. Their precise aetiology is not well understood and there is no curative treatment available, so they are considered highly contagious.
Lassa fever is endemic in parts of west Africa, probably harboured by bush rats. Death can result from general organ failure. Although the death rate in hospitalised patients in Africa is high, it is believed that there are many cases of mild or subclinical infection. An overall mortality rate of 1-2 per cent has been suggested^.
Even less is known about the Ebola virus and the related Marburg virus, but they do occasionally cause localised outbreaks carrying a 50-90 per cent mortality. The most serious complication is severe bleeding from the gastrointestinal tract, nose and gums. These outbreaks tend to occur in areas rarely visited by travellers. In addition, the problem is usually identified by the World Health Organisation and travel to the affected areas is restricted.