Specific Infections Affecting The Eyes In Travellers

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Ocular symptoms following travel are often a cause for great concern for both traveller and clinician alike. Some of the more esoteric and visually devastating ocular disease may well have been seen by travellers when visiting far-off countries such as India and Africa and South America. Travellers may then become anxious about whether they could have caught these diseases.

Snake Venom

The venom from spitting cobras can cause acute ophthalmic symptoms. They are found in Africa and Asia (Sumat-ran spitting cobra). Those snakes that are found in hotel lobby displays will be devenomised. The spitting cobra possesses great accuracy and can place venom in a victim's eye at up to 3 m. Fortunately, systemic toxicity does not occur; however, the venom binds to the cornea and causes corneal opacity, severe uveitis and blindness if not treated promptly.

The management is to irrigate immediately and copiously with any fluid that is to hand, preferably normal saline but any bland fluid, including milk, will do. To irrigate, get somebody to hold open the eyelids and pour fluid directly on to the cornea. If this is not possible due to severe blepharospasm, plunge the patient's head into bucket of water, to reduce the concentration of venom, and then retry. Use as much fluid as is possible, preferably 2-3 litres. Sedate the patient if you are having difficulty. Enlist the help of an ophthalmologist as soon as possible. The eye will look oedematous and inflamed with a whitish discharge. It will take some time for this to settle and the extent of damage to the be evaluated.

If a patient has been bitten, this is much more serious: be prepared for cardiovascular and neurological collapse.

River Blindness or Onchocerciasis

Life Cycle of the Onchocerciasis Vector

This disease is endemic in equatorial Africa and certain areas of Central and South America. Its prevalence is related to the presence of the blackfly. The blackfly is the insect vector that spreads the parasitic microfilarial infection between humans. Blackflies breed in fast-flowing rivers, hence the name river blindness; this explains why the infected populations are focused along river locations. The parasite is spread when an infected human host is bitten by the female blackfly. The microfilaria becomes a larva in the fly. These then are passed on to another human host by biting. The larvae migrate through subcutaneous tissues and eventually develop into adults after 12 months, producing characteristic nodules, typically around the pelvis or head (onchocercomas). The adult worms mate and produce millions of microfilariae, which migrate through the tissues and into the eye and skin.

The infection risk from one bite of a blackfly is about 1 in 10 and many repeated bites over a period of time are probably needed to establish infestation. The actual bite of a blackfly is usually unnoticed, although a painful wheal often develops, subsiding in a few days. Ocular disease, although eventually blinding, is delayed in onset and needs repeated reinfections to establish.

Bee Stings

Bee stings around the ocular tissue are common but rarely serious. Incidents of multiple stings from African bees have been reported. Stings on the cornea have also been reported.

Management. Reassure the patient. The eye and lid may be grossly swollen and look alarming. This will resolve. Remove the sting and give antihistamines if there is a large amount of swelling. A cold compress may also help. If corneal sting has occurred, a whitish opacity will be seen on the normally clear cornea associated with chemo-sis and congestion. Refer to an ophthalmologist for treatment with steroid drops. Cellulitis due to infection can follow a bee sting.

Symptoms and Signs

Skin infestation always accompanies eye disease, with pruritus, hyperkeratosis, depigmentation or hyperpig-mentation, as well as nodules. Skin snips are used commonly to make the diagnosis.

Early stages of the ocular infection may not be observed without a slit lamp to see the microfilariae swimming in the anterior chamber or in the cornea. The patient is asked to bend over to increase the load of microfilariae in the anterior chamber. When the micro-filariae die they become more obvious due to inflammatory reactions. The cornea can take on the appearance of cracked ice, or have snowflake opacities. The retina and optic nerve can also be affected, with mottling of the retina and fibrosis. Optic nerve inflammation causes swelling and, in the later course of the disease, atrophy.

Reducing Risk

The traveller need not worry unnecessarily about contracting the disease unless going to endemic regions for a period of some years. Obviously it would be wise always to avoid being bitten by insects in areas of the world where insect vectors are common; this can be achieved by the use ofinsect repellent, covering bare skin and sleeping under nets.

Treatment should be managed by experienced clinicians because violent reaction to drug treatments is common, as millions of parasites are killed simultaneously, often leading to more damage, such as optic atrophy.

Trachoma

Trachomal conjunctivitis is seen in populations where there are close-knit living conditions, poverty and poor hygiene. It used to exist in the British Isles only a few decades ago in crowded living conditions, for example in Glasgow and Dublin. It is encountered now in the Middle East, Africa, Indonesia and Central and South America. Trachoma has been largely eradicated from India as a result of effective public health measures.

Chlamydia trachomatis has several strains, which cause different forms of conjunctivitis. The more common strain in the UK and USA is the milder form, which causes inclusion conjunctivitis. This form is more likely to be contracted by the less careful traveller, as it is sexually transmitted and can be easily transferred from genitalia to conjunctiva by fingers. Serotypes A, B and C of C. trachomatis cause classical trachoma.

Signs and Symptoms

Trachoma is usually a chronic disease with repeated reinfection; initial symptoms are usually of an irritable red eye with mucopurulent discharge. Symptoms may be mild and ignored, but after 2-3 weeks characteristic changes occur. These take the form of follicles, easily seen by naked eye when everting the lid. Without treatment, symptoms are seen to resolve after 8-12 weeks, or at least abate, but continuing reinfection in susceptible patients leads to blinding complications. Blinding occurs because of extensive corneal scarring; as a consequence of conjunctival scarring, which leads to distortion of the eyelid margin, entropion and trichiasis, and inward-growing lashes, the cornea suffers from repeated abrading from lashes and poor lubrication. None of these long-term complications would be seen if a patient who contracted trachoma were adequately treated and reinfection did not occur.

Trachoma Infection Reduction

Trachoma has been eradicated in Europe due to in creased hygienic living conditions and disposal of waste. In the developing world it is usually spread by eye-seeking flies that feed off the ocular discharge. It is a sad fact that the blinding disease is entirely preventable by simple hygiene measures, yet is still affecting millions. The infection rate could easily be reduced by educating mothers to keep eyes and hands clean, and the frequent removal of waste from around living quarters, which could reduce the number of flies that also carry the infection to the faces of small children. Regular treatment of infection as it occurs, with a tube of cheap antibiotic such as tetracyc-line, could reduce reinfection and therefore prevent future long-term damage.

Diagnosis and Management of Chlamydial Infection in Travellers

The correct diagnosis involves a conjunctival scrape sent in special chlamydia transport medium (which should be available from a sexual health clinic or gynaecology department). The scrape must include conjunctival cells so it must be done quite firmly with a spatula. A smear can also be made from the scrape on to a glass slide, which will give a quick diagnosis, although serotyping will be necessary. If the sample is taken inadequately or in the wrong medium, the condition will go undiagnosed. The use of chloramphenicol before sampling reduces the rate of pick-up.

The patient can be treated with either oral or topical tetracycline or erythromycin. If the genitourinary form of chlamydia is suspected, it may be best to refer the patient to an appropriate clinic so that partners are also treated.

Those with chronic disease who have developed trichiasis and dry eye need specialist help. Entropion surgery, electryolysis and tear film supplements will help ease symptoms and prevent corneal scarring.

Loa loa

Infection with this filarial worm is not that uncommon in peoples from the equatorial rainforest of Central and West Africa. A biting fly of the genus Chrysops transmits the microfilariae. They develop into adult worms in the human host. The thought that a patient may have this infestation usually strikes revulsion in the westerner, but the people who live in this area are well used to its occurrence.

Symptoms

The symptoms are usually initially ignored by clinicians who are not familiar with the disease. These symptoms include itching, oedema and the patient reporting the feeling of something moving around the eye. Usually another member of the family has had a look in the eye and seen the translucent adult worm, which moves freely under the conjunctiva and subcutaneous tissues.

L. loa can survive for many years, evading capture. When they eventually die, they lead to a more severe reaction in the eye, with sudden severe swelling and itching. This gradually subsides and the tissues recover. (This swelling is sometimes called a Calabar, as it is common in the Calabar region of Nigeria.) The presence of L. loa is not associated with any visual loss.

The treatment is either physical removal or oral diethyl carbamazine. Physical removal is easier said than done. It involves the patient waiting in a darkened room until they feel the worm moving around the eye. At that point the clinician instils topical anaesthetic, preferably cocaine, and then makes a grasp for the worm with artery forceps. Then an incision is made in the conjunctiva to remove the worm. This usually involves some degree of skill and experience.

Leprosy

Leprosy is found in Africa, Asia and South America. The highest incidence is in Central and West Africa, but it is also seen in the Indian subcontinent among poorer communities. A quarter of a million leprosy patients are blind. There still remains uncertainty about how leprosy is contracted but it seems that close contact with an open case is necessary. Leprosy has not been seen in western Europe since the end of the 1800s. This is probably due to increased levels of hygiene. The organism prefers a cooler temperature and in the eye it is found in the lids, cornea, sclera and iris. Symptoms take 2—7 years to develop because the bacilli take 2 weeks to double in number. Clinical symptoms depend on the immunity of the patient. There is therefore a spectrum of disease, with two extremes called tuberculoid and lepromatous leprosy.

Ocular Involvement

Some of the systemic early signs that are seen include a seventh nerve palsy, erythema nodusum and joint pain. Leprosy does not always involve the eyes but it can be seen early on in the disease, so it is important to recognise this. There is madarosis or loss of eyebrows and eyelashes. Facial skin becomes thickened and nodular, especially the eyelids. Facial nerve palsy is often bilateral and therefore less obvious. The face loses its expression (lep-romatous stare). Discrete characteristic changes in the cornea and anterior chamber can be seen. There is thickening of corneal nerves and corneal anaesthesia with secondary corneal ulceration. Iritis is common in advanced cases, with iris pearls and granulomatous change.

Treatment

Treatment is with dapsone, introduced in the 1940s, rifampicin and clofazimine. There are now problems with resistance, just as occurs in tuberculosis. Multiple drug regimens are usually used. BCG affords some protection against leprosy and a vaccine is being developed. Ocular involvement requires specialist referral usually to a corneal or uveitis clinic for specific treatments.

The likelihood of a traveller catching leprosy is small, in view of high levels of immunity and hygiene, and should not really be a concern.

Lyme Disease

The ocular manifestations of this tick-borne disease are unusual. Lyme disease is caused by the spirochaete Borrelia burgdorferi, which is spread by ixodid ticks and also by biting flies, carried on the white-tailed deer. This disease is endemic in parts of the USA, especially Connecticut, but also in Australia and Asia. In Britain it is seen in the New Forest. Ten per cent of patients have an early follicular conjunctivitis; a keratitis can follow months later, resembling adonoviral infection. Episcleritis, uvei-tis, vasculitis and ocular myositis can occur in later stages. A dramatic presentation is a seventh nerve palsy, but other cranial nerve palsies, including optic neuropathy, can also occur. In endemic regions, 25% of new cases of Bell palsy is due to Lyme disease.

Treatment

Doxycycline 100mgb.d. or amoxicillin for children is effective in early stages. Later stages may need high dose penicillin or cephalosporin.

Toxoplasmosis

This organism is an obligate intracellular parasite. Humans become infected when eating undercooked meat, such as pork, beef or lamb, and possibly unpasteurised milk products; and if hands are contaminated with cysts following handling of cat litter trays. Infection at this stage is often not recognised. Symptoms like those of a mild 'flu are experienced. It is only when a pregnant woman is infected for the first time that serious consequences arise. Women who have positive antibodies to toxoplasmosis cannot transmit the disease. The parasite is spread transplacentally, to the fetus, with varying outcomes, depending on the gestational age of the fetus. In early pregnancy, stillbirth can occur. In the first trimester, neurological involvement can result in convuslions and mental handicap. In severe cases, ocular involvement results in scarring at the macula of the retina, but most milder cases can go unrecognised (Figure 22.31), until later in childhood or adult life when there could be a reactivation of old healed chorioretinitis, when dormant cysts rupture. Although infection is more likely later in a pregnancy, due to increased placental blood flow, the

Mio Mondo Una Sfera Cristallo
Figure 22.31 Toxoplasmosis scar

consequences of infection in early pregnancy are more serious.

Pregnant women should not eat undercooked meat in the UK or abroad, to avoid vertical transmission. In France, steak tartare should be avoided. Barbecued meats should be well grilled or avoided.

BLINDNESS: A GLOBAL PROBLEM

Cataract

Cataract accounts for around 50% of global blindness. In 2000 about 10 million cataract operation were performed throughout the world. It is estimated that this will need to increase to 32 million a year by 2020 to address blindness from cataract.

Trachoma

Blindness from trachoma occurs in poor communities. It is estimated that 146 million people, mainly children, carry active infection and 5.9 million, mainly adults, are blind from trachoma. Treatment and control is based around facial cleanness, regular instillation of antibiotics in children, lid surgery to those with lid scarring and environmental cleanliness.

Onchoceriasis

It is estimated that 18 million people are infected and 300 000 are blind from onchoceriasis, mainly in Central Africa and Central America. Control programmes are centred on the larvicidal spraying of blackfly breeding sites and the distribution of ivermectin annually. The resulting decrease in infection is dramatic.

Travelling in the developing world, people from Britain are likely to be shocked by the number of people with poor vision they encounter—not only elderly people, although most causes of blindness are age-related, but also those of working age and children. Travellers must inevitably wonder why so many people have poor vision and what can be done to prevent or cure blindness.

Seventy-five per cent of those who are blind live in developing countries. As the populations of these countries are both ageing and increasing, the present level of blindness, at 45 million blind globally, is set to increase to 75 million in the next 20 years, given present levels of eye care provision. Eighty per cent of blindness is either preventable or treatable: the challenge is therefore to increase the provision of eye care globally. In the light of this, the World Health Organization, the International Agency for the Prevention of Blindness and nongovernmental development organisations held meetings to develop a strategy for action to control avoidable blindness. As a result of these meetings, the programme 'Vision 2020: the right to sight', was announced, with the mission statement: 'To eliminate the main causes of blindness in order to give all people of the world, particularly the millions of needlessly blind, the right to sight.' The strategies put forward include widespread use of paramedical workers, a community approach with mobile health workers, and prioritisation and cost analysis. In the first 5 years of a 25 year programme the focus will be on cataract surgery, trachoma, onchoceriasis, childhood blindness and refractive error.

Childhood Blindness

The causes of childhood blindness vary from country to country. The major causes include vitamin A deficiency, often associated with measles, ophthalmia neonatorum and infections from the use of traditional eye medicines. Good hygiene and adequate nutrition are important to prevent blindness in this group. Some countries that are becoming industrialised, particularly in Latin America, have high levels of retinopathy of prematurity.

Refractive Errors

The provision of spectacles at an affordable price is one of the simplest ways of improving quality of life and income.

Vision 2020

The goals of the global initiative are achievable by simple and cost-effective means. Good eyesight makes an enormous personal and economic difference to whole families and communities, as well as to the individual involved. Prevention and treatment of blindness is one of the most important health issues of the twenty-first century.

Principles and Practice of Travel Medicine. Edited by Jane N. Zuckerman Copyright © 2001 John Wiley & Sons Ltd ISBNs: 0-471-49079-2 (Hardback); 0-470-84251-2 (Electronic)

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