Onchocerca volvulus transmission in the Mbam valley of Cameroon following 16 years of annual community-directed treatment with ivermectin, and the description of a new cytotype of Simulium squamosum.
Cameroon
Elimination
Ivermectin
Mbam
Onchocerca volvulus
Onchocerciasis
Simulium damnosum
Simulium squamosum
Journal
Parasites & vectors
ISSN: 1756-3305
Titre abrégé: Parasit Vectors
Pays: England
ID NLM: 101462774
Informations de publication
Date de publication:
02 Nov 2021
02 Nov 2021
Historique:
received:
27
08
2021
accepted:
16
10
2021
entrez:
3
11
2021
pubmed:
4
11
2021
medline:
1
1
2022
Statut:
epublish
Résumé
The onchocerciasis focus surrounding the lower Mbam and Sanaga rivers, where Onchocerca volvulus is transmitted by Simulium damnosum s.l. (Diptera: Simuliidae), was historically the largest in the southern regions of Cameroon. Annual community-directed treatment with ivermectin (CDTI) has been taking place since 2000, but recent studies have shown that new infections are occurring in children. We aimed to investigate blackfly biting and O. volvulus transmission rates along the lower Mbam river 16 years after the formal onset of annual CDTI. Black flies were collected for three consecutive days each month between July 2016 and June 2017 at two riverside villages and two inland sites situated 4.9 km and 7.9 km from the riverside. Specimens collected at each site were dissected on one of the three collection days each month to estimate parity rates and O. volvulus infection rates, while the remaining samples were preserved for pool screening. In total, 93,573 S. damnosum s.l. black flies were recorded biting humans and 9281 were dissected. Annual biting rates of up to 606,370 were estimated at the riverside, decreasing to 20,540 at 7.9 km, while, based on dissections, annual transmission potentials of up to 4488 were estimated at the riverside, decreasing to 102 and 0 at 4.9 km and 7.9 km, respectively. However, pool screening showed evidence of infection in black flies at the furthest distance from the river. Results of both methods demonstrated the percentage of infective flies to be relatively low (0.10-0.36%), but above the WHO threshold for interruption of transmission. In addition, a small number of larvae collected during the dry season revealed the presence of Simulium squamosum E. This is the first time S. squamosum E has been found east of Lake Volta in Ghana, but our material was chromosomally distinctive, and we call it S. squamosum E2. Relatively low O. volvulus infection rates appear to be offset by extremely high densities of biting black flies which are sustaining transmission along the banks of the lower Mbam river.
Sections du résumé
BACKGROUND
BACKGROUND
The onchocerciasis focus surrounding the lower Mbam and Sanaga rivers, where Onchocerca volvulus is transmitted by Simulium damnosum s.l. (Diptera: Simuliidae), was historically the largest in the southern regions of Cameroon. Annual community-directed treatment with ivermectin (CDTI) has been taking place since 2000, but recent studies have shown that new infections are occurring in children. We aimed to investigate blackfly biting and O. volvulus transmission rates along the lower Mbam river 16 years after the formal onset of annual CDTI.
METHODS
METHODS
Black flies were collected for three consecutive days each month between July 2016 and June 2017 at two riverside villages and two inland sites situated 4.9 km and 7.9 km from the riverside. Specimens collected at each site were dissected on one of the three collection days each month to estimate parity rates and O. volvulus infection rates, while the remaining samples were preserved for pool screening.
RESULTS
RESULTS
In total, 93,573 S. damnosum s.l. black flies were recorded biting humans and 9281 were dissected. Annual biting rates of up to 606,370 were estimated at the riverside, decreasing to 20,540 at 7.9 km, while, based on dissections, annual transmission potentials of up to 4488 were estimated at the riverside, decreasing to 102 and 0 at 4.9 km and 7.9 km, respectively. However, pool screening showed evidence of infection in black flies at the furthest distance from the river. Results of both methods demonstrated the percentage of infective flies to be relatively low (0.10-0.36%), but above the WHO threshold for interruption of transmission. In addition, a small number of larvae collected during the dry season revealed the presence of Simulium squamosum E. This is the first time S. squamosum E has been found east of Lake Volta in Ghana, but our material was chromosomally distinctive, and we call it S. squamosum E2.
CONCLUSIONS
CONCLUSIONS
Relatively low O. volvulus infection rates appear to be offset by extremely high densities of biting black flies which are sustaining transmission along the banks of the lower Mbam river.
Identifiants
pubmed: 34727965
doi: 10.1186/s13071-021-05072-y
pii: 10.1186/s13071-021-05072-y
pmc: PMC8561987
doi:
Substances chimiques
Insecticides
0
Ivermectin
70288-86-7
Types de publication
Journal Article
Langues
eng
Sous-ensembles de citation
IM
Pagination
563Subventions
Organisme : Departement Economie, Wetenschap en Innovatie
ID : 2014 SOFI 12
Organisme : H2020 European Research Council
ID : 671055
Organisme : Deutsches Zentrum für Infektionsforschung
ID : TI 03.907
Informations de copyright
© 2021. The Author(s).
Références
Parasit Vectors. 2016 Aug 05;9(1):432
pubmed: 27494934
Tropenmed Parasitol. 1976 Dec;27(4):438-54
pubmed: 12601
Bull Soc Pathol Exot. 1998;91(2):178-82
pubmed: 9642481
Lancet Infect Dis. 2018 Nov;18(11):1278-1286
pubmed: 30268645
Med Vet Entomol. 2001 Jun;15(2):219-23
pubmed: 11434559
Acta Trop. 2018 May;181:50-59
pubmed: 29410302
PLoS Negl Trop Dis. 2021 Jan 19;15(1):e0008926
pubmed: 33465080
BMC Vet Res. 2018 Jul 3;14(1):214
pubmed: 29970084
Trans R Soc Trop Med Hyg. 2004 Sep;98(9):520-8
pubmed: 15251400
Int J Infect Dis. 2016 Aug;49:1-8
pubmed: 27210267
Parasit Vectors. 2016 Nov 14;9(1):581
pubmed: 27842567
Parasit Vectors. 2015 Mar 19;8:167
pubmed: 25889256
Trans R Soc Trop Med Hyg. 1992 Jan-Feb;86(1):67-71
pubmed: 1566312
Am J Trop Med Hyg. 2017 Dec;97(6):1843-1845
pubmed: 29187277
Parassitologia. 1977 Jan-Aug;19(1-2):95-102
pubmed: 754135
Ann Trop Med Parasitol. 2011 Jun;105(4):277-97
pubmed: 21871165
BMJ Open. 2021 Sep 2;11(9):e050341
pubmed: 34475178
Infect Dis Poverty. 2016 Jun 27;5(1):66
pubmed: 27349645
Med Vet Entomol. 2004 Sep;18(3):296-300
pubmed: 15347398
Infect Genet Evol. 2010 Oct;10(7):846-65
pubmed: 20624485
Ecohealth. 2009 Jun;6(2):296-310
pubmed: 19915917
Lancet. 2002 Jul 20;360(9328):203-10
pubmed: 12133654
Science. 1986 Feb 14;231(4739):740-2
pubmed: 3753801
Ann Trop Med Parasitol. 2003 Jun;97(4):381-402
pubmed: 12831524
Trans R Soc Trop Med Hyg. 2002 Sep-Oct;96(5):537-41
pubmed: 12474484
Parasit Vectors. 2013 Jul 13;6:205
pubmed: 23849451
Ann Trop Med Parasitol. 1997 Jun;91(4):379-91
pubmed: 9290845
Trans R Soc Trop Med Hyg. 1978;72(6):675-6
pubmed: 734734
Ann Trop Med Parasitol. 2004 Jul;98(5):509-23
pubmed: 15257801
Onderstepoort J Vet Res. 1983 Sep;50(3):173-7
pubmed: 6646658
Am J Trop Med Hyg. 1984 Jul;33(4):586-94
pubmed: 6476202
Trop Med Int Health. 2007 Nov;12(11):1342-53
pubmed: 18045261
Int Health. 2018 Mar 1;10(suppl_1):i40-i48
pubmed: 29471342
Tropenmed Parasitol. 1975 Mar;26(1):111-38
pubmed: 1145723
Open Forum Infect Dis. 2020 Jun 02;7(6):ofaa206
pubmed: 32587878
Trop Med Parasitol. 1993 Sep;44(3):223-44
pubmed: 8256103
PLoS Negl Trop Dis. 2017 Aug 14;11(8):e0005849
pubmed: 28806785
Parasitology. 1998 Apr;116 ( Pt 4):349-62
pubmed: 9585937
Acta Trop. 2013 Jan;125(1):43-52
pubmed: 22995985
PLoS Negl Trop Dis. 2014 Apr 24;8(4):e2824
pubmed: 24762816
Tropenmed Parasitol. 1975 Mar;26(1):88-97
pubmed: 1145728
Parasit Vectors. 2019 Mar 19;12(1):114
pubmed: 30890155