Schistosomiasis

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Schistosomiasis, or bilharzia, is a disease caused by parasitic trematode worms of the genus Schistosoma. There are five species that are widely known to infect humans S. japonicum, S. mansoni, S. haematobium, S. intercalatum, and S. mekongi. Among the five, only one is found in the Philippines. Twelve regions in the country are endemic for schistosomiasis, affecting 28 of the 79 provinces, with 1,152 endemic villages in 169 municipalities. This parasitic disease is common among farmers, fishermen and their families. More than 200 million people are affected worldwide, but in the Philippines, it is one of the leading causes of morbidity, outranked only by malaria and tuberculosis.

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Infection

Humans get infected through contact with contaminated freshwater. Cercariae, the parasitic larvae of the trematode, penetrate the human skin within a few seconds, even when unbroken. As these larvae enter the human body, they migrate to the lungs to reach the liver. After about 45 days, the larvae mature into adult worms. Male and female worms mate and relocate to their final site, the host’s blood vessel. Numerous eggs are produced everyday by the female worm. These eggs break from the blood vessel and transfer to the intestine or urinary bladder. It is through the excreta of the host that the eggs leave the human body. Once in contact with water, the eggs hatch and become miracidia, an intermediate larval form. Miracidia look for a freshwater snail, penetrate it and use it as intermediate host to maintain survival. In the Philippines, S. japonicum specifically infects the amphibian snail Oncomelania. It is inside the snail’s body that miracidia reproduce asexually to form multitudes of cercariae, which leave the snail and enter the water again, ready for infection.

Symptoms

Most people are asymptomatic during the early phase of infection. It is the eggs, not the worms that cause the body’s reaction to infection. Itchy skin or rashes may develop within a few days after infection. After 1-2 months, fever, chills, cough, and muscle pain may occur. There may be bloody or mucoid stools, diarrhea, and dystenteric attacks. Internal organs that are affected are the ones usually inhabited by the parasite: liver, lungs, intestines, and the bladder. Inflammation or scarring occurs in these organs and after several years without treatment may cause severe damage. There can be liver and spleen enlargement, weight loss, severe liver disease, anemia, jaundice, and ascites in the later stage of the disease. Heart failure may arise as a complication. On rare occasions, the parasites settle in the brain or spinal cord and cause seizures, paralysis, and spinal cord inflammation. Children who are repeatedly infected may develop anemia, malnutrition, and learning difficulties.

Diagnosis and Treatment

Stool and urine analysis are the common methods for detecting infection. A blood test has been developed, but is not available in the Philippines yet.

Modern drug treatments use praziquantel, oxamniquine, and metrifonate. Praziquantel is effective in the elimination of all forms of schistosomiasis. Oxamniquine is used in South America and Africa to treat intestinal schistosomiasis. Metrifonate is utilized for urinary schistosomiasis. In the Philippines, the Department of Health established the Schistosomiasis Control Program, which aims to reduce the prevalence of the disease to 1% in 2010. The program’s objectives are as follows:

  • To sustain the elimination status (disease prevalence below 1%) in special target areas/provinces of Bohol, Zamboanga del Norte, Surigao del Sur, Misamis Occidental,and Davao Oriental
  • To increase the coverage of Mass Treatment to 80% of eligible population in the barangay with prevalence rate of 10% above (baseline is 30%)
  • To increase the percentage of households with sanitary facilities in endemic areas to 72% (baseline is 60%)
  • To increase the percentage of households with access to safe water in endemic areas to 82% (baseline is 75.5%)
  • Increase the coverage of footbridge construction wooden/concrete) in cercaria-infested bodies of water frequented by people to 10% (baseline is 3.5%)
  • Increase the coverage of footbridge construction (wooden/concrete) in cercaria-infested bodies of water frequented by people to 10% ( baseline is 3.5%, foreign assisted projects)


To control morbidity, the program employs both mass and selective treatment. Among its strategies are:

  • Health technology transfer on the management of schistosomiasis, disease & vector surveillance to local health personnel
  • Strengthening of referral system in strategic areas
  • Technical assistance to all stakeholders in trainings, projects development and research
  • Advocacy/health promotions thru tri-media
  • Social mobilization/community organization
  • Forging partnerships with Local Government Units, Non-Government Organizations, Private Organizations such as Farmers Organizations, Irrigators associations, BHWs organizations
  • Networking/Linkaging and collaboration with the Academe, National Government Agencies on Agriculture, National Irrigations Administration, BAI, DepED, DPWH, DENR, LGUs
  • Snail control through environmental modifications
  • Surveillance of cases and snail vectors
  • Resource generation through foreign assisted projects/public investment packages
  • Policy and human resource development
  • Health impact assessment of pipeline and existing water development projects
  • Quality assurance/quality control


Research during the past five years utilized tools of molecular biology, immunology, and epidemiology to develop a potential vaccine using antibody isotypes that recognize S. japonicum antigens. Investigators are currently looking forward to the possibility of using the monkey Macaca fascicularis as a vaccine model for schistosomiasis infection. Other projects that are underway include refinement of S. japonicum detection process using the immunodot ‘SJ-URIDIP’ kit; a study on the pathogenesis and immunology of protection of F. gigantica infection for S. japonicum infection in water buffaloes and sheep; and investigations on the mechanisms of infection in relation to puberty.

Prevention

Precautionary measures include:

  • Avoiding swimming or wading in freshwater when you are in places in the country for which schistosomiasis is endemic.
  • Drinking safe water. Iodine treatment alone does not guarantee safety from parasites. Filtering or boiling water for 1 minute before drinking will kill any dangerous parasites, bacteria, or viruses present.
  • Heating water for bathing for 5 minutes at 150°F. Water held in a storage tank for at least 48 hours should be safe for showering.
  • Vigorous towel drying after an accidental, very brief water contact may prevent penetration of the parasite. However, towel drying should not be relied on to prevent schistosomiasis.

References


Citation

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