ArticlesSchistosomiasis in Lake Malawi
Introduction
Schistosomiasis (ie, snail fever or bilharzia) is a parasistic infection caused by trematodes (flukes).WHO estimates that at present 200 million people are infected and 600 million are at risk world-wide. Three major species of schistosomes infect human beings: Schistosoma haematobium primarily causes genitourinary disease, whereas S mansoni and S japonicum primarily cause intestinal and hepatosplenic disease. Human beings are infected through skin contact with free-swimming cercariae that develop in freshwater snails
Schistosomiasis has been endemic in Malawi for several decades.1 Surveys have identified schistosomiasis in villages near Lake Malawi, but this finding has generally been attributed to local streams and rivers rather than the lake itself.1 The open waters and shorelines of Lake Malawi have long been considered risk-free with respect to schistosomiasis transmission.2, 3 As a consequence, tourist guides have described Lake Malawi as one of the last “schistosomiasis-free” freshwater lakes in Africa.4
In 1992 two US Peace Corps volunteers (PCVs) in Africa developed severe schistosomiasis of the central nervous system due to S haematobium, a manifestation of this infection that is considered extremely rare.5, 6 Sporadic reports of schistosomiasis among visitors to Malawi7, 8, 9, 10, 11, 12, 13, 14 suggest that some of these cases may have resulted from recreational freshwater exposure at Cape Maclear National Park (figure 1).
The two cases of central nervous system schistosomiasis within a short space of time suggested that transmission of schistosomiasis might be occurring among expatriates and tourists in Malawi. The possibility of a change in the epidemiology of schistosomiasis in Malawi, particulary in the southern lake region, prompted us to begin an investigation of the problem in 1993. We now report our findings.
Section snippets
Objectives
The principal objectives of the investigation were to determine if transmission of schistosomiasis was occurring in the heavily touristed southern region of Lake Malawi, and to assess the risk to tourists and expatriates of acquiring schistosomiasis during recreational freshwater exposure at popular resort areas in the southern lake region.
Epidemiologic survey
Participants were enrolled in Malawi in a retrospective, cross-sectional cohort study and serosurvey during March and April, 1993. Participants were enrolled
Seroepidemiologic investigation
955 participants were enrolled in the study (500 male, 455 female). The paricipants' countries of origin (33% USA, 20% UK, 11% South Africa, 26% other African countries, 5% other European countries, 4% Asia, and 2% South America) generally reflected the overall distribution of expatriates in Malawi (table 2). The US cohort included 96 of 101 PCVs and more than 50% of all Department of State officials in Malawi.
The overall seroprevalence of ASA was 33% (303 of 919 from whom serum was available)
Discussion
This study highlights the magnitude of schistosomiasis among expatriates and visitors to Malawi, and demonstrates, for the first time, that recreational freshwater exposure in Lake Malawi is an important source of transmission. Among 955 study participants, the seroprevalence of ASA was 33%; age-specific seroprevalence peaked at 54% among teenagers, who we thought likely to spend the most time in the lake. The high (12%) prevalence among children under 5 years suggests that transmission is
References (21)
- et al.
Schistosomiasis in expatriates returning to Britain from the tropics: a controlled study
Lancet
(1986) - et al.
MRI in schistosomiasis of conus medullaris and lumbar spinal cord
Lancet
(1993) - et al.
Early chemotherapy of imported neuroschistosomiasis
Lancet
(1993) - et al.
Schistosomiasis in Malawi-review
Trop Med Parasitol
(1985) Schistosomiasis in Malawi
BMJ
(1993)Schistosomiasis in US Peace Corps Volunteers-Malawi,1992
MMWR
(1993)- et al.
Involvement of the central nervous system in Schistosoma mansoni and S haematobium infection: review
Brain
(1985) - et al.
Lesions of schistosomiasis warts on the vulva
BMJ
(1993)
Cited by (118)
Schistosoma haematobium infection with pulmonary involvement in a traveller returning from Congo: A case report and systematic review of literature on nodular pulmonary schistosomiasis
2021, Travel Medicine and Infectious DiseaseCitation Excerpt :Among travellers, the GeoSentinel network reported 410 cases of travel-associated schistosomiasis over a decade (1997–2008), with a total of 83% cases acquired in Africa [5,7], when individuals born in endemic areas were excluded. Schistosomiasis was shown to be one of the ten leading causes of morbidity among returning travellers, accounting for 2% of ill travellers returning from sub-Saharan Africa [7]. Schistosomiasis is endemic in certain provinces of the Democratic Republic of the Congo (DRC) and is spreading to formerly non-endemic regions [8].
Minimmally invasive resolution of a left ureteral stenosis after Schistosoma haematobium infection
2019, Urology Case ReportsCitation Excerpt :Schistosoma haematobium is an endemic parasite in Africa and Middle East that can affect travelers after a single exposure. It usually affects urinary system, especially the bladder, with hematuria as its main symptom and bladder squamous cell carcinoma as a severe complication.1 However, although less frequent, it can also result in upper tract involvement causing ureteral dilation, calcifications, strictures, squamous metaplasia and squamous cell carcinoma.2
Biologic Attributes of Organisms That Influence Their Epidemiology
2017, Infectious Diseases, 2-Volume SetGrowing population and ecosystem change increase human schistosomiasis around Lake Malaŵi
2014, Trends in ParasitologyAcute pulmonary schistosomiasis in travelers: Case report and review of the literature
2012, Travel Medicine and Infectious DiseaseCitation Excerpt :Travelers should be advised not to swim in freshwater in endemic areas (also because of the risks of viral hepatitis and leptospirosis). Unfortunately, this advice may go unheeded, or, as our case report highlights, the traveler may be mistakenly assured that a given activity (e.g., rafting62 or windsurfing10) or area is ‘safe’ by locals or tour guides. To reinforce this message, travelers should be advised of the potential short- and long-term problems associated with infection, and of the need to follow up with a physician if there is potential exposure.
Biomphalaria pfeifferi (Gastropoda: Planorbidae) in Lake Malawi and Upper Shire River, Mangochi District, Malawi: Distribution, Genetic Diversity and Pre-Patent Schistosome Infections
2023, Tropical Medicine and Infectious Disease