Gatrointestinal infections in returning travellersBugs, protozoa and worms

As summer draws to a close the practice nurse is likely to see returning travellers, often from exotic destinations, gap year travels and adventure. Some will bring unwanted souvenirs of their travels in the form of viral and bacterial diseases, and parasites

With cheaper air travel and an increasing sense of adventure there is really no limit to the kind of travel which people now consider tourism. And in line with the increasingly exotic destinations and style of travel, travellers can return with symptoms of unwelcome infections.

In this article we focus on gastrointestinal problems in returning travellers, looking at what they may be and how to diagnose them. An encyclopaedic knowledge of these conditions is perhaps not essential as we may encounter some of them only rarely. However we do need to know how to take a helpful history, how to investigate symptoms and what the possible causes are.

HOW BUGS ARE ACQUIRED

Most gastrointestinal (GI) and parasitic infections affecting the bowel are acquired via the faeco-oral route, often from contaminated soil — although some parasites enter the body through skin or mucous membranes, such as hookworms from soil and schistosomes from water.^1,2

It ought to be simple to avoid these infections — handwashing, careful attention to diet, drinking only bottled water, avoiding ice. But life is not that simple for travellers.

Bottled water may not be available or may be contaminated. It is impossible to maintain perfect hygiene where there is a lack of sanitary infrastructure. Water sterilization with tablets is imperfect, and some travellers find the resulting treated water unpalatable. Swimming pool water, river water and the sea may contain organisms from the human gut, human fertilizer may be used on crops, lack of adequate refrigeration makes food difficult to store and tropical climates favour reproduction of pathogens.

It may therefore, in practical terms, be impossible to — in the immortal words of the Washington-based Centers for Disease Control, 'avoid ingesting soil that may be contaminated with human faeces.'2

TAKING A HISTORY

When any patient presents with GI symptoms a question about recent travel is essential, and it is helpful not only to ask where they have been and for how long, but also to ask what kind of conditions they lived in.

The main focus of your history should centre on where the patient has been and how unwell they are. Not all GI infections need to be treated, but whether you will ultimately treat depends in part on how unwell the patient is.

The fact that a patient observed scrupulous hygiene is not proof against infection with almost anything — we are human, we have to eat, and from the moment we open our mouths to do so there is a route of access for all sorts of unfriendly creatures to do their worst.

GI infection by bacteria and protozoa typically causes diarrhoea, but may also cause altered taste, nausea, belching, vomiting, anorexia, malabsorption, bloating, offensive 'floaty' stools, excess flatulence which can be sulphurous, upper or lower GI pain, and acquired lactose intolerance. The presence of mucus in the stools suggests bowel inflammation, and the presence of blood suggests that the infection is invasive to the gut wall.

GI infection by helminths usually causes very little in the way of gastric upset and the only sign of their presence may be when they are felt at the anus or seen in the stool. However, there are exceptions to this.

WHO GETS GI UPSET?

High risk destinations include South America, Africa, parts of the Middle East and most of Asia: 20-50% of travellers to high risk areas develop diarrhoea.

Intermediate-risk areas include Israel, Japan, Southern Europe, South Africa and some of the Caribbean islands - about 20% of travellers to these destinations develop diarrhoea,

Low-risk areas include Northern Europe, North America, New Zealand and Australia: here less than 8% of travellers develop diarrhoea.

CAUSES OF GI UPSET BACTERIAL INFECTIONS

Bacterial diarrhoea causes abrupt onset of diarrhea with cramping pains. Nausea, vomiting and fever can occur. The diarrhoea often resolves spontaneously as the gut 'clears itself'. However, it can last for two weeks and throughout that period the patient is infectious, so it often makes sense to treat. To do so it's necessary to know what the infecting organism is. Treatment with the wrong antibiotic is likely to make the patient feel worse.

Treatment with the right antibiotic will dramatically shorten the illness. Unfortunately widespread empirical use of broad spectrum antibiotics in the developing world has led to widespread resistance.³

In up to 60% of episodes of traveller's diarrhoea, no pathogen is found.⁴ Organisms most commonly found in the remainder are listed in Box 1 and management options in box 2.

Giardia is a parasite that also causes diarrhoea, although the symptoms tend to appear slowly, typically about three weeks after initial infection. This will often be when the traveller has returned home.

Giardia causes a low-grade, chronic diarrhoea associated with flatulence and cramps. Travellers may refer to a sulphur taste when belching ('eggy burps') — although this is also common in many bacterial infections and is not particularly diagnostic. Metronidazole is the treatment of choice, but this can be an unpleasant drug to take and patients should be warned of its antabuse effect.

Amoeba This protozoan is a rare cause of chronic diarrhoea alternating with constipation. It can remain latent for a year or more. During this period it lives off the patients food in the gut, digesting it by secreting enzymes. Unfortunately it can occasionally do the same thing to the gut wall, and will then become invasive, causing bowel wall ulceration. Symptoms progress to mucousy and bloody stools, which is then referred to as "amoebic dysentery." Liver abscess can also result and severe disease can be fatal. Amoebicides such as metronidazole are used for invasive amoebic infection while paromomycin and iodoquinol are also used to get rid of the luminal organisms.

Cyclospora is a protozoan parasite that causes infections in the summer. It was virtually unknown before 1990 when it appeared in the US linked to contaminated raspberries. It causes diarrhoea with mild fever, which may be severe and watery. An outbreak in the USA began in July 2013 and has affected hundreds of people, but the source is still uncertain. It has a waxing and waning course over several weeks, and untreated is usually self limiting. The most effective treatment is septrin.

HELMINTHS

People just hate the idea of having worms, perhaps because you can see them. The film Alien crystallised all of our inner nightmares about parasites, but as with all horror it was based on a grain of truth; some helminthes can invade through body tissue and cause lasting damage. Fortunately in UK clinical practice such things are vanishingly rare.

Worms have plagued humans for millennia. They are described in the writings of Hippocrates, and in the Bible. They have altered the course of world history — for example acute schistosomiasis made China abandon her amphibious assault of Taiwan during the Cold War just long enough for American ships to relieve the island.

Helminth infections are targeted under the London Declaration on Neglected Tropical Diseases, a joint action of pharmaceutical companies and NGOs launched in January 2012. It aims to control/eradicate helminthic diseases by 2020, by ensuring necessary supply of drugs and promoting sanitation and health education.¹¹ For now, though, millions of the world's poorest have chronic helminth infections, and every year hundreds of travellers will return with infestations considered normal in the developing world but still relatively unusual here.

There are two major families of helminths - nematodes (roundworms) including the major intestinal worms, and platyhelminths (flatworms), which include flukes and tapeworms.

The main species that infect people are the soil transmitted species - roundworm (Ascaris lumbricoides), the whipworm (Trichuris trichiura) and the hookworms (Necator americanus and Ancylostoma duodenale).¹⁰

Soil-transmitted helminths live in the intestine where they produce thousands of eggs each day that are passed in the faeces. Where environmental conditions are favourable, the eggs develop into infective stages. There is no direct person-to-person transmission or infection from fresh faeces because eggs need about 3 weeks in the soil before they become infective. Humans become infected when ingesting eggs or larvae in contaminated food.

Some worms gain access directly through the skin, including hookworm larvae. Hookworm is a voracious consumer of blood from the intestinal mucosa and can cause severe anaemia, although it is commonly asymptomatic and is in fact much smaller than the giant roundworm.

Tape worms fill patients with particular horror. The two most important human pathogens are the pork tapeworm and the beef tapeworm. Infection is acquired by eating imperfectly cooked contaminated meat and infected pork. The adult worm lives in the intestine and causes very few symptoms. It remains in the intestine until it reaches a length of about 1 metre (3 feet). It absorbs most of the host's digested food and the patient becomes weak. However, it is generally asymptomatic and is diagnosed when part of the worm (a segment) is passed in the stool.

Flukes do not tend to infect the gut, although they are also acquired by the faeco-oral route.

Presentation

Worms are generally asymptomatic, at least at first, although heavy infestation can lead to secondary symptoms. They are easy to detect if they are seen in the stools. They may also cause perianal itching, which can raise suspicion. Heavy loads of some worm types such as the giant roundworm (ascaris) can actually block the gut and cause abdominal pains, vomiting and sometimes fever and diarrhoea. It is also possible to develop an allergic response to parasites, leading to eosinophilia, oedema and joint pains.

Diagnosis can be difficult. For basic diagnosis, specific helminths and eggs can be generally identified from the faeces. However, there is considerable potential for error and for missing mixed infections. Serology and antigen testing can sometimes help.

Investigations

The most useful investigation for travellers' diarrhoea and suspected helminth infection will be stool examination and culture, including inspection for cysts, ova and parasites, culture and sensitivities.

Additionally a full blood count should be performed in patients who are particularly unwell, especially if there is blood in the stool.

More invasive testing such as sigmoidoscopy and biopsy is reserved for more chronic symptomatic infection.

Prevention and chemotherapy

Albendazole and mebendazole are recommended for treatment of roundworm and tapeworm infection, levamisole and ivermectin are prescribed for tapeworms; and praziquantel is used for schistosomiasis, tapeworms and flukes. These drugs can be difficult to obtain in the community in UK practice, and it may be necessary to obtain them from hospital pharmacy, in some cases on a named patient basis.

SUMMARY

Some of the things that travellers bring home in the gut are perfectly horrible, but they are not all as symptomatic as you might expect. Moreover diagnosis is difficult, and empirical antibiotic treatment unwise.

The practice nurse treating returning travellers needs to be aware of the possible gut infections that may be present in the traveller before her, including the possibility that more than one type of organism may be present. Good safety netting of patients, repeating simple investigations and thorough review of symptoms that do not settle is essential if the diagnosis is to be made.

REFERENCES

1. CIWEC clinic Kathmandu, Nepal. Understanding diarrhea in travelers. Available at: http://ciwec-clinic.com/health-information/understanding-diarrhea-in-travelers/

2. Center for Disease Control and Prevention (CDC). Prevention & control of ascariasis. Available at: http://www.cdc.gov/parasites/ascariasis/prevent.html

3. [No authors listed] What to do about travellers' diarrhea. Drug Therap Bull 2002; 40(5): 36-38.

4. Peltoal H, Gorbach SL. Traveler's diarrhea. Epidemiology and clinical aspects. In: DuPont HL, Steffen R (eds). Textbook of travel medicine and health. Second edition London: BC Becker, 2001.

5. DuPont HL. Systematic review: the epidemiology and clinical features of travellers' diarrhoea. Aliment Pharmacol Ther 2009;30(3):187-96

6. GP Notebook. Travellers' diarrheoa. Available at: www.gpnotebook.co.uk/simplepage.cfm?ID=-1939144699

7. D Bruyn G, Hahn S, Borwick A. Antibiotic treatment for traveller's diarrhoea. Cochrane Database Syst Rev. 2000, (3), CD002242 May 2000

8. Hill DR et al. The practice of travel medicine: guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2006; 43(12):1499-539.

9. CDC. Health information for international travel, 2014 ed. The pre-travel consultation. Self-treatable diseases: travelers' diarrhea. Available at: http://wwwnc.cdc.gov/travel/yellowbook/2014/chapter-2-the-pre-travel-consultation/the-pre-travel-consultation

10. WHO. Intestinal worms. Available at: http://www.who.int/intestinal_worms/en/

11. Hotez PJ, et al. Control of neglected tropical diseases. N Engl J Med 2007;357:1018—1027