sign in sign up
<<
Home , Schistosoma, Schistosoma haematobium, Schistosoma intercalatum, Schistosoma japonicum, Schistosoma mansoni, Schistosoma mekongi

From our Whitepaper Files: Be Aware of

> See companion document World Schistosomiasis 2015 Edition Risk Chart

Canada 67 Mowat Avenue, Suite 036 Toronto, Ontario M6K 3E3 (416) 652-0137 USA 1623 Military Road, #279 Niagara Falls, New York 14304-1745 (716) 754-4883 New Zealand 206 Papanui Road Christchurch 5

www.iamat.org | [email protected] | Twitter @IAMAT_Travel | Facebook IAMATHealth

THE HELPFUL DATEBOOK It was clear to him that this young woman must It’s noon, the skies are clear, it is unbearably have spent some time in or the Middle hot and a caravan snakes its way across the East where this type of is prevalent. When Sahara. Twenty-eight people on camelback are interviewed she confirmed that she had been heading towards the oasis named El Mamoun. in Africa, participating in one of the excursions They are tourists participating in ‘La Sahari- organized by the club. enne’, a popular excursion conducted twice weekly across the desert of southern Tunisia The young woman did not have at all, by an international travel club. In the bound- but had contracted schistosomiasis while less Sahara, they were living a fascinating swimming in the oasis pond. When investiga- experience, their senses thrilled by the majestic tors began to fear that other members of her grandeur of the desert. After hours of riding, group might also be infected, her date book they reached the oasis and were dazzled to see came to their aid. Many of her companions had Fig. 1 fresh-water . a clear pond fed by a bubbling spring. The idea exchanged addresses with this attractive young Image source: Eduardo Rivera (Shutterstock) of jumping into the cool water to relieve the lady, and eventually all members of the group intense heat must have been exciting. There was were contacted and examined. The toll was heavy a momentary pause at the pond’s edge to test – out of 28 persons, nine were added to the long the water, then the tourists waded in. Although list of travellers infected at El Mamoun.1 they had been warned never to wade or bathe in the freshwater in the tropics, the cool water THE LIFE OF THE was irresistible after travelling for so long under the scorching sun. The advice given at home How did it happen? The swimmers hadn’t was forgotten in the momentary relief of the noticed among the vegetation at the edge of the refreshing oasis pond. pond the presence of minute so small that a dozen would easily fit into a teaspoon. In some Milan – five months later. A pathologist was ponds and rivers as many as 1,000 can be found examining a cervical biopsy of a young woman in a square metre. They are the freshwater snails suspected of having cancer. Under the micro- belonging to the , which serve as scope, he was amazed to see some peculiar the specific hosts to the larval stages of the Schis- worm eggs. There was no doubt in his mind tosoma haematobium worm. that these were not the common worm eggs routinely seen in his work, but the eggs of the The Snail – flatworm called haematobium. The Creature Nurturing The eggs of the worm are eliminated via the The eggs of this worm damage the urinary of those infected. When an egg reaches freshwa- and genital tracts which become inflamed ter, it hatches rapidly – see picture of the life cycle and scarred. The , called Schistosomiasis of the schistosomes (1). The ensuing 1. Although Schistosomiasis cases are no (Bilharzia), is a languishing, debilitating (an immature form of life called miracidium) is longer reported from Tunisia, this true story highlights how the disease can go undetect- illness which saps the physical and mental an oval shaped organism clothed with minute ed in unsuspecting travellers. energies of its victims. cilia (2) swimming in search of the Bulinus snail.

Be Aware of Schistosomiasis | 2015 1 Fig. 2 Life cycle of human schistosomes.

Themiracidium [Gr.: meirákon = young form of – The Sexual Life of the Worm life] is attracted by the snail’s mucous secretion The tail-less cercariae, now called schistosomulae, and burrows into the soft tissue of the mollusc (e). then reach the lymph vessels which drain into Once inside, the miracidium transforms itself into the two major veins, allowing the schistosomulae an elongated, thin walled sack called mother of both sexes to reach first the and then the sporocyst [Gr.: sporá = sowing, seed; kústis = , where they mature and mate. sack] (3), which gives rise to about four hundred daughter sporocysts (4). Each one forms within its The have a rounded and elongated ap- cavity numerous fork-tailed cercariae [Gr.: kerkos pearance. In the kingdom they are placed = tail], representing the early stages of matur- under the group Platyhelmintes (Gr.: platús = ing worms. A single miracidium may produce broad; élmis = worm). They are greyish-white thousands of cercariae in only six weeks and this in colour and measure between 1/2 and 1 inch production may carry on in the snail for months. (1.2-2.5 cm) in length and have two suction discs for adhesion and feeding. They belong to The water in the pond of El Mamoun was teem- the of flukes or (Gr.: tre – ma ing with this kind of microscopic life when our = hole) and are commonly called ‘blood flukes’ tourists arrived at the oasis. Previous visits to the because they live in the blood vessels of mam- oasis by Bedouins had left the pond infected, a mals. The name for their genus, Schistosoma (Gr.: legacy of the disease for the tourists to contract. schistós = cleft, split; soma = body), indicates their difference from all other flukes: They are Like divers jumping from their boats, the not hermaphroditic, but have two genders – cercariae, stimulated by the bright light and the male and female. When they mate, the edges of high temperature of the day, abandon the snails. the larger male worm fold over to form a groove Seen under the microscope they look like minia- to hold the slender and longer female close to ture tadpoles, with a pear shaped buoy and a him (8). Then, tightly embraced, they leave the long tail ending in a y-shaped fork which acts as liver, swimming against the flow of the venous a propeller to move the organism through the blood, to settle in the blood vessels surrounding water (5). They are now swimming in a desparate the bladder and the adjacent organs in the geni- race against time, searching for a human to to-. Fig. 3 Electron micrograph of a male/female pair of adult schistosomes. ensure their survival. They will die within 48 hours if the search fails. The reason? Since the only way to ensure the Image source: Natural History Museum, London survival of the is to get the eggs into Attracted by the oily secretion lubricating freshwater, the worms live close to the natural the human body, they attach themselves to the openings of the human body – the bladder or with their oral suckers. They do not need the openings of the reproductive organs – so that to find a wound or break in the skin since the eggs can easily escape to the outside. they secrete an which splits the ‘cement’ holding the cells of the skin together (6). The human body doesn’t suspect their presence As soon as the cercariae start to penetrate the because the worms disguise themselves with a outer layers, they shed their tails (7) and burrow coating of similar to that of the host. a tunnel through the . This coating fools the human’s defense system,

IAMAT Whitepaper Files 2 which otherwise would fight off foreign particles. • lives Undisturbed, the worms may live for years in the blood vessels of the bladder producing an incredible number of eggs. and genitalia. The eggs, characterized by a terminal spike (d), are passed The Eggs – The Quest for Freedom with urine. The intermediate host The eggs, which are oval-shaped with a snail belongs to the genus Bulinus spike protruding from one end, are deposited in which has a conical shaped shell, large numbers in the tissue of the bladder. Some dark grey in colour measuring about reach the innermost part through the tiniest of 1 cm in length (d1). The infection blood vessels. They are now only separated from caused by S. haematobium is found the urine by a thin layer of tissue, which they in Africa (including ) and pierce with the spike to allow them to fall into the . Humans are the the urine. When the eggs are eliminated from only known reservoir of this species, the bladder and reach , they will therefore, with improved hatch into miracidia, search out the snails, and public health initiatives the and start the cycle anew. prospects of eradication are excellent in communities who are infected with However, a great number of eggs remain S. haematobium only. trapped in the tissue. Unlike their shrewd parents, they are not able to cheat the defense • lives in the In countries where system of the host. Immediately, they are blood vessels surrounding the large Schistosomiasis is endemic, surrounded by scores of white blood cells, bowel. The eggs, which have a lateral avoid contact with fresh water. the body’s main defense system. These spine (c), are passed with the stools. ‘immune fighters’, known as phagocytes The intermediate host belongs to the There will be situations (Gr.: phagein = to eat; kútos = ), fend off genus Biomphalaria, a snail with a flat where you will be tempted whatever they recognize as foreign by grind- disc-shaped shell (c1), dusky brown to disregard this simple advice. ing the invaders to bits and swallowing them or reddish in colour with a diameter There is no risk in seawater. up with . However, the phagocytes are of 7-22mm. The infection caused powerless in their fight against so many giants, by S. mansoni is endemic in Africa each one 10 times their size. (including Madagascar), the Arabian peninsula, , , and some Not even with the help of larger cells, countries. Besides humans, the (Gr.: macrós = big; phagein = S. mansoni also infects and to eat), which fuse to form giant cells, are able monkeys () in some endemic to turn the battle in favour of the host. They are areas which contribute to maintaining only able to lay siege by completely surround- the cycle and making ing the eggs forming (L.: granulum elimination more difficult. = small grain) in the bladder tissue. Within about a month the eggs die and their shells • lives mainly calcify into rigid structures forming polyps, in the blood vessels of the small nodules, and ulcers. Slowly these are replaced intestine. The eggs, which have a by fibrous scar tissue, making the bladder wall rudimentary lateral spine (b) escape rigid and thicker causing constriction especially into the bowel and are passed with on the lower portion of the (the tubes stools. The intermediate host is a carrying urine from the kidneys to the bladder) small amphibious snail of the genus impairing the outflow of urine. This produces (b1). It has a turreted back pressure, dilating the ureters and (tower-like) shell, dark olive in colour, reducing the functioning of the kidneys. Finally measuring about 1cm in length. The the accumulation of waste in the blood infection caused by this worm occurs in poisons the human body resulting in death. , the and in limited areas of Central Sulawesi, Indonesia. THE FLATWORM IN HUMANS S. japonicum is primarily a zoonotic (animal) infection with multiple Of the thousands of different species of reservoir hosts: Rodents, dogs, , living as parasites in practically water buffalo, pigs, horses, and every kind of vertebrate, only 8 are , making elimination efforts responsible for the human disease challenging and very costly. schistosomiasis. Each species has a specific intermediate host a suitable species of • was identified in , in which the larva undergoes 1978. It is found along the Mekong further development: River in Cambodia and Laos.

Be Aware of Schistosomiasis | 2015 3 • was identified (scarred liver) leads to the accumulation in 1988 as the cause of human of fluids in the abdomen, producing infection on peninsular Malaysia and a clinical picture similar to of Malaysian Borneo. the liver.

• Schistosoma guineensis was identified • The infection caused by S. japonicum in 2003. It is found in western Africa, follows a course similar to that of mainly in , Equatorial S. mansoni, but the disease tends to Guinea, Gabon, Sao Tomé and Príncipe, be more severe due to the large number Nigeria, Burkina Faso, and Mali. of eggs produced by this species (an Mapping of this species is not complete. average of 3,000 eggs per female worm a day). Infection with S. mekongi and • is present in S. malayensis tend to be milder than the Democratic Republic of the Congo. S. japonicum. It is usually the sole transmission agent but can also be found in areas • The infection by S. guineensis and where S. mansoni and S. haematobium S. intercalatum runs a rather mild course, are present. sometimes without symptoms.

• Schistosoma mattheei is found in Schistosomiasis lacks the immediate effects southern Africa (South Africa, of other tropical . It is a chronic Swaziland, Zambia) and primarily affects condition produced by the cumulative damage A Brief History of cattle, horses, sheep and antelopes, of repeated egg deposits, making you vulnerable but can infect humans. It co-exists with to other , including HIV, and can be Schistosomiasis: S. mansoni and S. haematobium. fatal. This silent drama unfolds slowly among It is believed that both populations in rural and agricultural areas. schistosomes and snail hosts THE DISEASE – Even the suburbs of some African, Asian, and have been in contact with THE DAMAGE BY THE EGGS South American cities are infected. In many areas humans since our evolutionary the disease is so common that it is regarded as The early signs of the disease caused by a way of life. In fact, in some parts of Africa origins. From the area of the the different species of worms are similar. it is not considered unusual for a person to Great Lakes in , When the cercariae penetrate the skin, they pass blood with urine. Today, it is estimated the infection moved produce itching and a localized at the point that 249 million people throughout the world, northward along the of entry which disappears within a day or two, mainly in sub-Saharan Africa, are affected and later reached the followed by a symptomless period of 4 to 6 by the disease. weeks during which the worms reach Middle East and maturity. Towards the end of this period, A MAJOR CONCERN through trade routes. you start to feel weak, suffer loss of appetite, experience night sweating, and have a pro- The worldwide demand for water requires new nounced rash resembling hives all over the irrigation projects and the construction of dams The movement of East African tribes contributed to spreading the disease to the body. A late afternoon lasting from 5 to 10 has resulted in the spread of the disease where south. From west Africa the infection was days is known as ‘snail fever’ or Katayama it previously did not exist. transported to the Americas by the slave Fever. The French call it ‘fièvre des safaris’ trade and it became established in and some Caribbean Islands due to (safari fever). A case in point is the construction of the the presence of suitable snail hosts. Schisto- in Ghana creating Lake Volta somiasis was known to the ancient civiliza- tions of , Mesopotamia, and China. After a few months, when the infection is in 1965. The project displaced 80,000 people, well established, the damage produced by the mostly subsistence farmers and fishermen from 1500 B.C. The Egyptian Papyrus Ebers mentions remedies “to kill worms in the body discharge of eggs into the tissues of the various 700 villages who were resettled into 52 new causing blood in the urine”. Calcified eggs organs will manifest itself in different ways based communities. In a short period after construc- of S. haematobium, found in two mummies of on the type of worm. tion of the dam, the proportion of the popula- the XXth dynasty by Sir Marc Armand Ruffer in 1910 substantiate this evidence. tion affected by Schistosomiasis jumped to 40% • The passage of blood in urine and from the previous 5%. 400 B.C. Ge Hong in his classic compendium of traditional Chinese medicine frequent and painful urination are ‘Zhouhou Beiji Fang’, describes “water consistent symptoms of the disease In Egypt, construction of the Aswan Dam al- poison attacking man like ‘shegong’ S. haematobium [a poisonous insect], but invisible”. caused by . tered the balance between the two types of infec- tion present in the country. Ecological changes 1851 Theodor Bilharz, a German physician • Bouts of with the passage favouring the spread of Biomphalaria snails, working at the Kasr el Aini Hospital in Cairo discovered trematoda worms in the veins of a of blood and mucous in the stools which harbours S. mansoni (affecting the liver patient during an . He realized they were are the signs of the infection caused by and large bowel) increased, while the urinary the cause of Schistosomiasis. In honour of his discovery, the disease is called Bilharzia, a term S. mansoni. In the late stages of the form caused by S. haematobium decreased. widely used in Europe. illness, extensive of the liver With a successful national Schistosomiasis

IAMAT Whitepaper Files 4 In temperate areas, the cercariae  Important... of non-human schistosomes affect wild birds and ducks and are known So what exactly is to penetrate human skin. Swimmer’s Itch? After swimming in a lake a person may experience itching and a mild irritation of the skin. The cercariae, which have entered the wrong host, will not reach the blood circulation but will die at the point of entry.

This condition, known as Swimmer’s Itch, is found all over the world.

control program, prevalence of both are also contributing with large drug donations. S. haematobium and S. mansoni infections Since 2006, due to educational awareness are now on the decline. programs and the yearly distribution of chemotherapy, many endemic countries have In other desert areas such as Saudi Arabia experienced a significant decrease in human and Iraq, the limited volume of water (ponds, infections.Some countries no longer report small canals and temporary streams) makes human infections and are awaiting evaluation prospects for eradication of the disease possible. and confirmation by the WHO that human Elimination of snails and treatment of infected transmission has been interrupted. See IAMAT’s persons in these areas are sufficient World Schistosomiasis Risk Chart for country to block transmission. details. However, the majority of endemic coun- tries still require massive help with public health In many countries, particularly in and improved sanitation, this is to say, chemo- sub-Saharan Africa, the problem is still therapy campaigns must be combined with infra- waiting to be solved. Rivers and lakes are structure improvements – safe water and sewage an integral part of domestic life in rural disposal – education, and snail control to communities where water is used for achieve permanent success. consumption, clothes washing, bathing, 1902 The British physician Patrick Manson TREATMENT found schistosome eggs in the stools of a patient and playing. Only a combination of health from Antigua suffering from intestinal schisto- education with the introduction of effective somiasis. This suggested to him that this form sanitation such as piped deep well water The drug of choice for the treatment of of the disease was caused by another species, which later was named S. mansoni in his honour. and the efficient disposal of human waste Schistosomiasis is , a compound can prevent Schistosomiasis transmission. effective against all species of schistosomes. 1904 Fujiro Katsurada discovered a third species of schistosomes in Japan and named The drug is well tolerated and fast acting. it S. japonicum. TURNING TO HOPE

1908 Pirajá Silva was the first doctor to describe Praziquantel paralyzes the worms, making them the life cycle of the disease. Since 1985 the WHO expert committee vulnerable to the body’s defense mechanisms. on schistosomiasis has recommended However, successful treatment will improve but 1909 Akira Fuginami and Hachitaro Nakamura proved that the schistosomes’ entry route is chemotherapy as the main control strategy not solve the situation; treated persons can easily through intact skin. against the infection. Large scale distribution become re-infected. Prevention is still preferable

1913 Keinosuke Miyairi and Masatsagu Suzuki of the drug praziquantel was officially adopted by to treatment since in the absence of obvious observed the penetration of miracidia into the the WHO assembly in 2001 and this symptoms, irreversible damage may be done specific snails, and by dissecting them, were able to describe the transformation of the miracidium strategy has been integrated into public health before the infection is detected. into sporocysts and finally into cercariae. programs in many affected countries. Many non-profit organizations, such as the The targets for the interruption of the 1915 R. T. Leiper, working in Egypt, identified the two snail species which transmit Carter Foundation and groups working to transmission cycle are public education, S. haematobium and S. mansoni. The complete eliminate neglected tropical diseases have incor- improved sanitation and disposal of human lifecycle of the major human schistosomes and their snail vectors was finally clarified. porated the distribution of praziquantel into their waste, elimination of snails, and treatment health care programs. Pharmaceutical companies of infected persons.

Be Aware of Schistosomiasis | 2015 5 PERSONAL PREVENTION

No drugs are available to prevent the establish- • Avoid contact with freshwater during ment of the infection although progress has peak daylight hours when the cercariae been made in the development of a vaccine for emerge from the snails and are most the schistosomes that affect domestic . active. Attempts to develop a vaccine for human schis- tosomes have not yet been successful. • If you accidentally come into contact with freshwater, rub your skin The Golden Rules to immediately with rubbing alcohol and Prevent Schistosomiasis a dry towel to reduce the possibility of infection. • In countries where Schistosomiasis is endemic, avoid contact with fresh water. • If you are travelling overland by car, carry There will be situations where you will be a pair of rubber gloves in case you have to tempted to disregard this simple advice. dip your hands into a stream or pond to There is no risk in seawater. See IAMAT’s get water for the radiator. World Schistosomiasis Risk Chart for country details. • Water from a river or lake used for 1978 Marietta Voge, David Bruckner and John I. Bruce confirmed that S. mekongi bathing and washing should be boiled or is a separate species from S. japonicum. • If you are planning a trip into the jungle chlorinated. or desert, make sure it is a short one, 1988 S. malayensis was identified as a separate species from S. japonicum by so that you can withstand the heat and • Water for washing and bathing is G. J. Greer, C. K. Ow-Yang, and H. S. Yong. are not tempted to cool off in a pond or relatively safe if it has been stored for 2-3

2003 S. guineensis was identified as a separate stream. Make sure you do not run out of days (the period generally accepted as the species from S. intercalatum by a team of scien- purified water. life span of cercariae), provided that the tists from Cameroon, France, and England. container is free of snails. 2009 & 2012 Research teams decoded • If you must pass through streams or S. mansoni and S. japonicum (2009) and swamps, wear high waterproof boots or • Drinking water should be boiled or S. haematobium genomes (2012) opening up the possibility for new types of drug treatments. hip waders. treated with chlorine tablets, as the cercariae may burrow through the mucosa

Sources: Please contact IAMAT for references. • Stay away from the banks of streams and of the mouth. rivers; snails abound in shallow water where they feed on organic waste and • Make sure vegetables are well cooked aquatic vegetation. Snail presence is and avoid salads since the leaves may have minimal in the deeper ends of lakes, been washed with infected water. For rivers, and streams where water tends to advice on water and food precautions, flow faster. see www.iamat.org.

IAMAT Whitepaper Files 6 GUIDELINES FOR SNAIL IDENTIFICATION

It is not always easy, even for a trained person, to distinguish harmful snails from harmless ones. Snail features vary from continent to continent. The following hints will help you identify intermediate snail hosts. Always wear a pair of rubber gloves to hold snails for examination.

Africa • Look for the dimensions of the snail. genus Biomphalaria Harmful ones will have a shell less than (x 1.5 natural size) 2 cm (3/4 inch) in length. • Harmful snails are always in the water, either floating, lying on the bottom or attached to aquatic vegetation. Snails crawling on land are harmless. • Harmful snails do not have an operculum, genus Bulinus a ‘door’ attached to the foot which closes (natural size) the opening of the shell when the snail retreats. In Africa, harmless snails have an operculum.

Harmful snails are divided into two major groups: Harmful snail Harmless snail 1) Snails with a flat, round shell like a (left-hand opening) (right-hand opening) disc or wheel belong to the genus Biomphalaria, which is the intermediate host of S. mansoni. 2) Snails with a conical shell ending with a sharp tip belong to the genus Bulinus, which transmit S. haematobium.

You may identify the harmful Bulinus species by holding the shell between your fingers with the opening facing you and the apex pointing upwards. You are dealing with a harmful species if the opening is to the left hand side. Shells with a right hand opening belong to harmless snails.

South America and Some Caribbean Islands The only harmful species of snail present genus Biomphalaria of the in the western hemisphere belong to the genus western hemisphere Biomphalaria. Except for B. straminea, (natural size) they differ from the African species in that they are larger than 2 cm (3/4 inch) in length. They have a round, flat-shaped shell, dark brown, sometimes reddish in colour.

Southeast In , the snails transmitting genus Oncomelania schistosomiasis belong to the genus Onco- (x 2.4 natural size) melania. They have a conical, turreted dark brown shell, usually less than 1 cm (1/2 inch) in length. You may notice that in this dangerous species the opening is to the right and when the snail retreats, the operculum will close the opening. You will find them either floating in water or crawling on land.

Be Aware of Schistosomiasis | 2015 7