Schistosoma intercalatum

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Schistosoma intercalatum
S interculatum eggS.jpg
Egg of Schistosoma intercalatum
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Trematoda
Order: Diplostomida
Family: Schistosomatidae
Genus: Schistosoma
Species:
S. intercalatum
Binomial name
Schistosoma intercalatum
Fisher, 1934

Schistosoma intercalatum is a parasitic worm found in parts of western and central Africa. There are two strains: the Lower Guinea strain and the Zaire strain. S. intercalatum is one of the major agents of the rectal form of schistosomiasis, also called bilharzia. It is a trematode, and being part of the genus Schistosoma , it is commonly referred to as a blood-fluke since the adult resides in blood vessels.

Contents

Humans are the definitive host and two species of freshwater snail make up the intermediate host, Bulinus forskalii for the Lower Guinea strain and Bulinus africanus for the Zaire strain. [1]

Morphology

The clinically defining characteristic of most schistosome species are their eggs' size and shape. The eggs of Schistosoma intercalatum have a terminal spine and tend to be moderately larger than those of S. haematobium (approximately 130 × 75  μm). The origin of the name 'intercalatum' is from the observation that their eggs are of an intermediate range between the smaller S. haematobium and larger S. bovis. [2] These eggs are unique because they will stain red when exposed to the Ziehl–Neelsen technique, aiding in identification. [3] When viewed using scanning electron microscopy, it can be observed that the S. intercalatum's surface has a much lower amount of integumental elevations, or bosses, than S. mansoni. This feature is consistent with the tegument appearance of other terminally spined schistosomes. [4]

Life cycle

Schistosoma intercalatum's life cycle is very similar to that of S. haematobium, except for some key differences. To start the life cycle, the human host releases eggs with its feces. In water, the eggs hatch to become miracidia, which penetrate the freshwater snail intermediate host. [5] S. intercalatum has two major strains, each with its own preferred bulinid host. The Zaire strain will use Bulinus africanus, while the Lower Guinea strain will use the extremely common B. forskalii as its intermediate host. [6] The miracidia penetrate the snail tissue, and inside they become sporocysts and multiply. The sporocysts then mature into cercariae inside the snail host and are ready to leave. The cercariae are free-swimming in the surrounding water until they find their definitive host: a human. If there is a small temperature change, the cercariae of S. intercalatum will form concentrated aggregates near the surface of the water. This mechanism for body heat detection of a potential host restricts the formation of viable cercariae to small streams and slow moving bodies of water because of their high sensitivity. [1]

The cercariae penetrate through the human's skin and lose their tail, becoming schistosomulae. The schistosomulae then migrate to the hepatic portal system of the liver to mature into adults. As adults, they make their way to the inferior mesenteric vein and mate, producing thousands of eggs. [5] These eggs migrate down to the mesenteric venules of the colon and form polyps as the eggs attempt to cross into the lumen. S. intercalatum's eggs are specific to the colon, making them unique among the infectious African schistosomes. [7]

Epidemiology

S. intercalatum is at risk of endangerment in large part due to the introduction of invasive species into its native habitat. Since 1973, both S. mansoni and S. haematobium have been found in places that have been traditionally inhabited by S. intercalatum. This is thought to be because of the increase in transportation accessibility and the increase in forestry jobs in these habitats. [3] Male S. mansoni and S. haematobium will both take priority over S. intercalatum when it comes to mate selection, leading to a smaller proportion of female S. intercalatum available for mating. While crosses with S. mansoni give no viable offspring, the pairing with a male S. haematobium will result in a hybrid organism. Most hybrids will have a diluted genome that is more closely related to S. haematobium, helping to bring about a decline in S. intercalatum populations. The other obstacle restricting the parasite's population growth is its selective distribution. The cercariae are very particular over where they develop, needing small, forested areas with streams to infect their human host. There are only a few of these regions in Africa, and they decrease in size every day due to deforestation. [1]

Prevalence

In 2009, there were an estimated 200 million human infections of schistosomiasis. [8] In 1999, the noted number of S. intercalatum infections was 1.73 million. [9]

Distribution

There are two major strains of S. intercalatum, both living in forested areas of Africa. One strain lives in the Congo area, particularly Zaire, and the other strain lives in the Lower Guinea area, mainly in Cameroon. [10] Cameroon is a place of scientific interest because three species of human schistosomes live there. [1] Most relevant research conducted on S. intercalatum was performed in, or around, the Loum area in Cameroon.[ citation needed ]

Pathology

Symptoms

Symptoms of all forms of schistosomiasis are caused by the immune system's reaction to the eggs, rather than the adult worms themselves. [5] A few hours to days after cercariae invade the skin, some people experience pruritus and raised papules at the site of penetration. This is called cercarial dermatitis, also known as swimmer's itch. It can last up to a few weeks, although, this stage is usually asymptomatic in local populations. [11] S. intercalatum is associated with lower morbidity than the other schistosomes that infect humans. In a study done on schoolchildren in the Republic of São Tomé and Príncipe in western Africa—where S. intercalatum and S. haematobium are endemic—the only schistosome present in the sample was S. intercalatum, an overall prevalence of 10.9 percent in stool specimens. [12]

Unlike the more pathogenic species, infection with S. intercalatum is usually only associated with bloody stool, and sometimes splenomegaly. [12] Blood in the stool is caused by "inflammation, hypertrophy, and ulceration of the mucosa" of the intestine. [11] These signs can be difficult to interpret because affected populations are often infected with multiple intestinal parasites. Clinical presentation of an established S. intercalatum infection can be different in the local population and non-immune tourists. The majority of infections of foreign travelers are asymptomatic and go unnoticed. [13] Chronic schistosomiasis results in granulomata forming around eggs in the mesenteric vessels. [11]

Diagnosis

Diagnosis is usually made using clinical and epidemiological information. Infection with S. intercalatum can be distinguished from that of S. mansoni or S. haematobium based on where eggs manifest outside the body and the morphology of the eggs. In Africa, the only species of schistosome are S. intercalatum, S. mansoni, and S. haematobium. S. haematobium causes urinary schistosomiasis, so eggs will be shed in the urine; S. mansoni and S. intercalatum reside in the mesenteric venous plexus, so eggs will be shed in the feces. [5] Looking at the stool specimen under a microscope, the species can be distinguished; S. intercalatum eggs have a terminal spine (as seen in the figure above) and S. mansoni eggs have a lateral spine. [14]

Serologic testing looks for the presence of antibodies against the adult schistosome in the blood. This can only take place 6 to 8 weeks after initial infection in order for the parasite to reach the adult stage and the immune system to produce antibodies against it. However, serologic testing is not useful for patients with previous infections. [5]

Treatment

Praziquantel is an effective treatment against all species of Schistosoma that infect humans. Administering treatment at the correct time is important since the drug only works against the adult worm and there must be a strong antibody response from the immune system. Thus, it should be administered 6 to 8 weeks after suspected infection (contact with infested freshwater). There has been limited evidence on possible drug resistance among the schistosomes due to reports of low cure rates. Oxaminiquine is another treatment for schistosomiasis, but it is not widely available, nor is it routinely used. [5]

Related Research Articles

<span class="mw-page-title-main">Schistosomiasis</span> Human disease caused by parasitic worms called schistosomes

Schistosomiasis, also known as snail fever, bilharzia, and Katayama fever, is a disease caused by parasitic flatworms called schistosomes. The urinary tract or the intestines may be infected. Symptoms include abdominal pain, diarrhea, bloody stool, or blood in the urine. Those who have been infected for a long time may experience liver damage, kidney failure, infertility, or bladder cancer. In children, it may cause poor growth and learning difficulty.

<span class="mw-page-title-main">Trematoda</span> Class of parasitic flatworms

Trematoda is a class of flatworms known as flukes or trematodes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host, where the flukes sexually reproduce, is a vertebrate. Infection by trematodes can cause disease in all five traditional vertebrate classes: mammals, birds, amphibians, reptiles, and fish.

<i>Schistosoma</i> Genus of flukes

Schistosoma is a genus of trematodes, commonly known as blood flukes. They are parasitic flatworms responsible for a highly significant group of infections in humans termed schistosomiasis, which is considered by the World Health Organization as the second-most socioeconomically devastating parasitic disease, with hundreds of millions infected worldwide.

<span class="mw-page-title-main">Schistosomatidae</span> Family of flukes

Schistosomatidae is a family of digenetic trematodes with complex parasitic life cycles. Immature developmental stages of schistosomes are found in molluscs and adults occur in vertebrates. The best studied group, the blood flukes of the genus Schistosoma, infect and cause disease in humans. Other genera which are infective to non-human vertebrates can cause mild rashes in humans.

Schistosoma japonicum is an important parasite and one of the major infectious agents of schistosomiasis. This parasite has a very wide host range, infecting at least 31 species of wild mammals, including 9 carnivores, 16 rodents, one primate (human), two insectivores and three artiodactyls and therefore it can be considered a true zoonosis. Travelers should be well-aware of where this parasite might be a problem and how to prevent the infection. S. japonicum occurs in the Far East, such as China, the Philippines, Indonesia and Southeast Asia.

<i>Schistosoma mansoni</i> Species of fluke

Schistosoma mansoni is a water-borne parasite of humans, and belongs to the group of blood flukes (Schistosoma). The adult lives in the blood vessels near the human intestine. It causes intestinal schistosomiasis. Clinical symptoms are caused by the eggs. As the leading cause of schistosomiasis in the world, it is the most prevalent parasite in humans. It is classified as a neglected tropical disease. As of 2021, the World Health Organization reports that 236.6 million people have schistosomiasis and most of it is due to S. mansoni. It is found in Africa, the Middle East, the Caribbean, Brazil, Venezuela and Suriname.

<span class="mw-page-title-main">Swimmer's itch</span> Medical condition

Swimmer's itch, cercarial dermatitis or schistosome dermatitis is a short-term allergic contact dermatitis occurring in the skin of humans that have been infected by water-borne schistosomes, a type of flatworm. It is common in freshwater, brackish and marine habitats worldwide. The incidence of this condition may be increasing, although this may be attributed to better monitoring and reporting. Nevertheless, the condition is considered to be an emerging infectious disease.

<i>Schistosoma haematobium</i> Species of fluke

Schistosoma haematobium is a species of digenetic trematode, belonging to a group (genus) of blood flukes (Schistosoma). It is found in Africa and the Middle East. It is the major agent of schistosomiasis, the most prevalent parasitic infection in humans. It is the only blood fluke that infects the urinary tract, causing urinary schistosomiasis, and is the leading cause of bladder cancer. The diseases are caused by the eggs.

<i>Schistosoma malayensis</i> Species of fluke

Schistosoma malayensis is a schistosome parasite. It was first described in 1988 in Peninsular Malaysia and appears to be a zooenotic infection. The species is named after the country of Malaysia. The natural vertebrate host is van Müller's rat. The intermediate hosts are aquatic snails, Robertsiella kaporenisis. Among Robertsiella kaporenisis are two other Roberstiella species.

<i>Trematocranus placodon</i> Species of fish

Trematocranus placodon is a species of cichlid fish endemic to Lake Malawi, Lake Malombe and the upper reaches of the Shire River in Africa. It is mainly a shallow-water species that prefers to occupy areas with patches of Vallisneria, but it can occur as deep as 31 m (102 ft). It can reach a total length of up to 25 cm (9.8 in).

Bulinus nyassanus is a species of small air-breathing freshwater snail with a sinistral shell, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ramshorn snails and their allies. This species is endemic to Lake Malawi in Africa, where found both in shallow and relatively deep water. Its shell generally reached a size of up to around 14 mm × 11 mm.

Schistosoma indicum is a species of digenetic trematode in the family Schistosomatidae. The parasite is widespread in domestic animals in India and other Asian countries.

<span class="mw-page-title-main">Schistosomiasis vaccine</span>

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<i>Biomphalaria glabrata</i> Species of mollusc

Biomphalaria glabrata is a species of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails.

Schistosoma mekongi is a species of trematodes, also known as flukes. It is one of the five major schistosomes that account for all human infections, the other four being S. haematobium, S. mansoni, S. japonicum, and S. intercalatum. This trematode causes schistosomiasis in humans.

<i>Schistosoma spindale</i> Species of fluke

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<i>Bulinus forskalii</i> Species of gastropod

Bulinus forskalii is a species of tropical freshwater snail with a sinistral shell, an aquatic gastropod mollusk in the family Bulinidae, the ramshorn snails and their allies.

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<span class="mw-page-title-main">Trematoda in Kuwait</span>

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<span class="mw-page-title-main">Schistosoma hippopotami</span> Species of trematode

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References

  1. 1 2 3 4 Tchuem Tchuenté LA, Southgate, VR, Jourdane J, Webster BL, Vercruysse J (2003) Schistosoma intercalatum: an endangered species in Cameroon? Trends Parasitol19: 141-153.
  2. ↑ Fisher AC (1934) Study of the schistosomiasis of the Stanleyville district of the Belgian Congo. T Roy Soc Trop Med H28: 277-306.
  3. 1 2 Southgate VR (1976) Schistosomiasis at Loum, Cameroun. Parasitol Res49: 145-159.
  4. ↑ Kuntz RE (1977) Scanning electron microscopy of intergumental surfaces of Schistosoma intercalatum. J Parasitol63: 401-406.
  5. 1 2 3 4 5 6 "Parasites - Schistosomiasis" [Internet]. Atlanta (GA): Centers for Disease Control and Prevention. [updated 2010 Nov 2; cited 2011 Nov 7] Available from: https://www.cdc.gov/parasites/schistosomiasis/disease.html
  6. ↑ Jourdane J, Southgate VR, Pagès JR, Durand P, Tchuem Tchuenté LA (2001) Recent studies on Schistosoma intercalatum: taxonomic status, puzzling distribution and transmission foci revisited. Mem I Oswaldo Cruz96: 45-8.
  7. ↑ Rodriguez-Guardado A, Miquel R, Pérez R, Fresno M, Corachán M (2010) Colonic polyposis due to Schistosoma intercalatum. T Roy Soc Trop Med H104: 443-5.
  8. ↑ "Weekly Epidemiological Record" (2011). World Health Organization 86: 73-80.
  9. ↑ Crompton DW (1999) How much human helminthiasis is there in the world? J Parasitol85: 397-403.
  10. ↑ Bjorneboe A (1978) A comparison of the characteristics of two strains of Schistosoma intercalatum Fisher, 1934 in mice. J Helminthol53: 195-203.
  11. 1 2 3 Yamada T, Alpers DH, Kalloo AN, Kaplowitz N, Owyang C, Powell DW, editors (2008). Textbook of Gastroenterology. 5th ed. Hoboken (NJ): Wiley-Blackwell. Parasitic diseases: helminths; p. 2651-2671.
  12. 1 2 Almeda J, Corachan M, Soura A, Ascaso C, Carvalho JM, Rollinson D, Southgate VR (1994) Schistosomiasis in the Republic of São Tomé and Principe: human studies. Trans R Soc Trop Med Hyg88: 406-409.
  13. ↑ Corachan M (2002) Schistosomiasis and international travel. Clin Infect Dis35: 446-450.
  14. ↑ "Diagnostic Findings: Schistosomiasis" [Internet]. Atlanta (GA): Centers for Disease Control and Prevention. [updated 2010 Jan 7; cited 2011 Nov 7] Available from: http://dpd.cdc.gov/dpdx/html/Frames/S-Z/Schistosomiasis/body_Schistosomiasis_mic1.htm
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