Intestinal schistosomiasis in Uganda at high altitude (>1400 m): malacological and epidemiological surveys on Mount Elgon and in Fort Portal crater lakes reveal extra preventive chemotherapy needs.
BACKGROUND
Intestinal schistosomiasis is of public health importance in Uganda but communities living above 1400 m are not targeted for control as natural transmission is thought unlikely. To assess altitudinal boundaries and at-risk populations, conjoint malacological and epidemiological surveys were undertaken on Mount Elgon (1139 m-3937 m), in Fort Portal crater lakes and in the Rwenzori Mountains (1123 m-4050 m).


METHODS
Seventy freshwater habitats [Mount Elgon (37), Fort Portal crater lakes (23), Rwenzori Mountains (8) and Lake Albert (2)] were inspected for Biomphalaria species. Water temperature, pH and conductivity were recorded. A parasitological examination of 756 schoolchildren [Mount Elgon (300), Fort Portal crater lakes (456)] by faecal microscopy of duplicate Kato-Katz smears from two consecutive stool samples was bolstered by antigen (urine-CCA dipstick) and antibody (SEA-ELISA) diagnostic assays.


RESULTS
Biomphalaria spp. was found up to 1951 m on Mount Elgon and 1567 m in the Fort Portal crater lakes. Although no snail from Mount Elgon shed cercariae, molecular analysis judged 7.1% of snails sampled at altitudes above 1400 m as having DNA of Schistosoma mansoni; in Fort Portal crater lakes three snails shed schistosome cercariae. Prevalence of intestinal schistosomiasis as measured in schoolchildren by Kato-Katz (Mount Elgon = 5.3% v. Fort Portal crater lakes = 10.7%), CCA urine-dipsticks (18.3% v. 34.4%) and SEA-ELISA (42.3% v. 63.7%) showed negative associations with increasing altitude with some evidence of infection up to 2000 m.


CONCLUSIONS
Contrary to expectations, these surveys clearly show that natural transmission of intestinal schistosomiasis occurs above 1400 m, possibly extending up to 2000 m. Using spatial epidemiological predictions, this now places some extra six million people at-risk, denoting an expansion of preventive chemotherapy needs in Uganda.
Department of Parasitology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
Michelle C
MC
Stanton
Vector Control Division, Ministry of Health, Kampala, P.O. Box 1661, Uganda.
Moses
M
Adriko
Vector Control Division, Ministry of Health, Kampala, P.O. Box 1661, Uganda.
Moses
M
Arinaitwe
Department of Parasitology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
Alison
A
Howell
Department of Parasitology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
Juliet
J
Davies
Department of Parasitology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
Gillian
G
Allison
Department of Parasitology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
E James
EJ
LaCourse
Vector Control Division, Ministry of Health, Kampala, P.O. Box 1661, Uganda.
Edridah
E
Muheki
Vector Control Division, Ministry of Health, Kampala, P.O. Box 1661, Uganda.|Schistosomiasis Control Initiative, Imperial College London, London, W2 1PG, UK.
Narcis B
NB
Kabatereine
Department of Parasitology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK. russell.stothard@lstmed.ac.uk.
J Russell
http://orcid.org/0000-0002-9370-3420
JR
Stothard
D000293:Adolescent; D000531:Altitude; D000818:Animals; D000871:Anthelmintics; D002648:Child; D040362:Geographic Information Systems; D006801:Humans; D060106:Lakes / Q000469:parasitology; D011223:Praziquantel; D015995:Prevalence; D011315:Preventive Medicine; D012307:Risk Factors; D012550:Schistosoma mansoni / Q000235:genetics / Q000302:isolation & purification; D012555:Schistosomiasis mansoni / Q000453:epidemiology* / Q000469:parasitology* / Q000635:transmission*; D012908:Snails / Q000469:parasitology; D014454:Uganda / Q000453:epidemiology
D000871:Anthelmintics; D011223:Praziquantel
Biomphalaria; CCA; Kato-Katz; SEA-ELISA; Schistosoma mansoni; School children