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From our Whitepaper Files: Be Aware of > See companion document Schistosomiasis 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 Africa or the Middle hot and a caravan snakes its way across the East where this type of worm 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 cancer 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 Biomphalaria fresh-water snail. 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 FLATWORM 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 snails 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 genus Bulinus, 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 Schistosoma haematobium. The Creature Nurturing Infection The eggs of the worm are eliminated via the urine 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 disease, called Schistosomiasis of the human schistosomes (1). The ensuing larva 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 Humans – 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 lungs and then the sporocyst [Gr.: sporá = sowing, seed; kústis = liver, where they mature and mate. sack] (3), which gives rise to about four hundred daughter sporocysts (4). Each one forms within its The worms have a rounded and elongated ap- cavity numerous fork-tailed cercariae [Gr.: kerkos pearance. In the animal 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 family of flukes or Trematoda (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 host to to-urinary system. 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 species 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 skin 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 enzyme 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 protein similar to that of the host. a tunnel through the epidermis. This coating fools the human’s defense system, IAMAT Whitepaper Files 2 which otherwise would fight off foreign particles. • Schistosoma haematobium 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 Madagascar) and pierce with the spike to allow them to fall into the Middle East. Humans are the the urine. When the eggs are eliminated from only known reservoir of this species, the bladder and reach fresh water, they will therefore, with improved sanitation 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 • Schistosoma mansoni 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.