Vector competence of European mosquitoes for West Nile virus

Figures & data

Figure 1 European countries with human cases of West Nile fever reported to the European centre for disease prevention and control (ECDC). Colour gradient indicates the number of years during which cases of West Nile virus in humans have been reported since 2010. Reported cases are marked on the country level, except for the Balearic islands, Sicily, Sardinia, and Corsica, which are individually marked. Countries with no reported cases or no data available are marked in white. Data set provided by ECDC based on the data provided by WHO and Ministries of Health from the affected countries.

Figure 2 Schematic overview of the mosquito barriers to arbovirus infection. Schematic longitudinal cross-section of a mosquito. Arrows indicate the passage of virions through the midgut (MG) and salivary gland (SG) barriers. The dashed circle in the midgut represents the peritrophic membrane that is formed after ingestion of blood. Right inset: (i) Infection of midgut epithelial cells via binding to a putative receptor protein. (ii) Virus replication in midgut epithelial cells. (iii) Release of virus via budding from midgut epithelial cells and direct passage through the basal lamina into the haemocoel. (iv) Direct virus passage into the haemocoel through a ‘leaky’ midgut. (v) Virus infection of trachea after budding from midgut epithelial cells. (vi) Budding of virus from the trachea into the haemocoel. Left inset: (i) Infection of the salivary gland epithelial cells after passage through the basal lamina. (ii) Virus replication in the salivary gland cells. (iii) Virus release via budding from salivary gland cells into the salivary gland lumen. (iv) Virus release from the salivary gland cells into the salivary gland lumen via apoptosis.

Table 1 Overview of vector competence studies on West Nile virus with European mosquito species

Mosquito species	Mosquito origin (filial number)	WNV lineage (passage number)	Cell type virus propagation	Feeding method	Blood type	Infection assessment	Reported rates	References
Aedes albopictus	Spain (>F30)	Lineage 1 and 2 (−)	C6/36 or Vero E6	Hemotek with chicken skin membrane	Heparinised bovine blood with ATP	qRT-PCR	IR and DR	^Citation48
	Italy (−)	Lineage 1 (−)	-	Glass feeder with pig-intestine membrane	-	qRT-PCR	IR, DR, and TR	^Citation49
Aedes caspius	France (F0)	Lineage 1 (P5)	C6/36	Chicken skin membrane	Washed rabbit erythrocytes with ATP	IFA or qRT-PCR	DR and TR	^Citation22
Aedes detritus	United Kingdom (F0)	Lineage 1 (−)	Vero E6	Odorised feeding membrane	Heparinised human blood	qRT-PCR	TR	^Citation50
Aedes japonicus japonicus	Germany (F0)	Lineage 1 (−)	-	Cotton stick	Human blood with fructose and fetal calf serum	qRT-PCR	IR	^Citation51
Culex modestus	France (F3–4)	Lineage 1 (P5)	C6/36	Chicken skin membrane	Washed rabbit erythrocytes with ATP	IFA or qRT-PCR	DR and TR	^Citation22, Citation23
Culex torrentium	Germany (F0)	Lineage 1 (−)	-	Cotton stick	Human erythrocytes with fructose and fetal calf serum	qRT-PCR	IR and DR	^Citation52
Culex pipiens s.l.	France (F1)	Lineage 1 (P5)	C6/36	Chicken skin membrane	Washed rabbit erythrocytes with ATP	IFA or qRT-PCR	DR and TR	^Citation22
	Italy (F0, F7, or F11)	Lineage 1 (−)	Vero E6	Glass feeder with pig-intestine membrane	Rabbit blood with EDTA	qRT-PCR	IR, DR, and TR	^Citation53
	Italy (−)	Lineage 1 (−)	-	Glass feeder with pig-intestine membrane	-	qRT-PCR	IR, DR, and TR	^Citation49
	The Netherlands (−)	Lineage 2 (P2)	C6/36	Hemotek with Parafilm membrane	Chicken blood	CPE	IR and TR	^Citation54
	The Netherlands (−)	Lineage 1 and 2 (P2)	C6/36	Hemotek with Parafilm membrane	Chicken blood	CPE and IFA	IR and TR	^Citation55
Culex pipiens pipiens	Germany (F0)	Lineage 1 (−)	-	Cotton stick	Human erythrocytes with fructose and fetal calf serum	qRT-PCR	IR and DR	^Citation52
	The Netherlands (F3-F5)	Lineage 2 (P2)	C6/36	Hemotek with Parafilm membrane	Chicken blood	CPE	IR and TR	^Citation56
	The Netherlands (F4-F6)	Lineage 2 (P2)	C6/36	Hemotek with Parafilm membrane	Chicken blood	CPE	IR and TR	^Citation57
	Italy (F4-F6)	Lineage 2 (P2)	C6/36	Hemotek with Parafilm membrane	Chicken blood	CPE	IR and TR	^Citation57
Culex pipiens molestus	Spain (>F30)	Lineage 1 and 2 (−)	C6/36 or Vero E6	Hemotek with chicken skin membrane	Heparinised bovine blood with ATP	qRT-PCR	IR and DR	^Citation48
	Germany (−)	Lineage 1 (−)	-	Cotton stick	Human erythrocytes with fructose and fetal calf serum	qRT-PCR	IR	^Citation52
	The Netherlands (−)	Lineage 2 (P2)	C6/36	Hemotek with Parafilm membrane	Chicken blood	CPE	IR and TR	^Citation56
Culex pipiens Hybrid (pipiens x molestus)	Spain (>F30)	Lineage 1 and 2 (−)	C6/36 or Vero E6	Hemotek with chicken skin membrane	Heparinised bovine blood with ATP	qRT-PCR	IR and DR	^Citation48
	The Netherlands (F1)	Lineage 2 (P2)	C6/36	Hemotek with Parafilm membrane	Chicken blood	CPE	IR and TR	^Citation56

Abbreviations: cytopathic effect, CPE; dissemination rate, DR; immunofluorescence assay, IFA; infection rate, IR; quantitative reverse transcription-PCR, qRT-PCR; transmission rate, TR. Hyphen indicates that used variable was not reported in the study.

Listed are important methodological variables that were used in studies with European mosquito species.

Table 2 Transmission rates of European mosquito species for West Nile virus

Mosquito species	Mosquito origin	WNV lineage (Origin, year)	WNV titer in blood meal	Incubation temperature	Incubation period	Infection rate (n)	Dissemination rate (n)	Transmission rate (n)	References
Aedes albopictus	Italy	Lineage 1 (Italy, 2011)	9.3 × 10^7 PFU/mL	27 °C	0	100 % (5–7)	0 % (5–7)	0 % (5–7)	^Citation49
					3	20 % (5–7)	0 % (5–7)	0 % (5–7)
					9	40 % (5–7)	40 % (5–7)	0 % (5–7)
					14	80 % (5–7)	40 % (5–7)	40 % (5–7)
					21	20 % (5–7)	20 % (5–7)	20 % (5–7)
					28	20 % (5–7)	20 % (5–7)	20 % (5–7)
Aedes caspius	France	Lineage 1 (France, 2000)	2.0 × 10^10 PFU/mL	26 °C	14	-	1 % (124)	0 % (42)	^Citation22
Aedes detritus	United Kingdom	Lineage 1 (New York, 1999)	2.0 × 10^6 PFU/mL	21 °C	17	-	-	21 % (78)	^Citation50
Culex modestus	France	Lineage 1 (France, 2000)	2.0 × 10^10 PFU/mL	26 °C	14	-	91 % (22)	40 % (5)	^Citation23
						-	89 % (37)	55 % (22)	^Citation22
Culex pipiens s.l.	France	Lineage 1 (France, 2000)	2.0 × 10^10 PFU/mL	26 °C	14	-	39 % (234)	16 % (57)	^Citation22
	Italy	Lineage 1 (Italy, 2011)	9.3 × 10^7 PFU/mL	27 °C	0	100 % (5–7)	0 % (5–7)	0 % (5–7)	^Citation49
					3	100 % (5–7)	0 % (5–7)	0 % (5–7)
					9	100 % (5–7)	0 % (5–7)	0 % (5–7)
					14	60 % (5–7)	20 % (5–7)	20 % (5–7)
					21	80 % (5–7)	80 % (5–7)	60 % (5–7)
					28	71 % (5–7)	71 % (5–7)	43 % (5–7)
				28 °C	32	55–90 % (112)	28–90 % (112)	21–33 % (112)	^Citation53
	The Netherlands	Lineage 2 (Greece, 2010)	4.0 × 10^7 TCID50/mL	28 °C	14	46 % (-)	-	33 % (-)	^Citation54
		Lineage 1 (New York, 1999)	1.4 × 10^8 TCID50/mL	23 °C	14	49 % (131)	-	22 % (67)	^Citation55
		Lineage 2 (Greece, 2010)	1.4 × 10^8 TCID50/mL	23 °C	14	33 % (154)	-	24 % (79)	^Citation55
Culex pipiens pipiens	The Netherlands	Lineage 2 (Greece, 2010)	5.7±1.0 × 10^7 TCID50/mL	18 °C	14	29 % (50)	-	0 % (50)	^Citation56
				23 °C	14	50 % (50)	-	6 % (50)
				28 °C	14	63 % (50)	-	33 % (50)
	Italy	Lineage 2 (Greece, 2010)	4.2±1.0 × 10^7 TCID50/mL	18 °C	14	28 % (50)	-	0 % (50)	^Citation57
				23 °C	14	36 % (50)	-	2 % (50)
				28 °C	14	32 % (50)	-	16 % (50)
	The Netherlands	Lineage 2 (Greece, 2010)	4.2±1.0 × 10^7 TCID50/mL	18 °C	14	26 % (50)	-	0 % (50)	^Citation57
				23 °C	14	34 % (50)	-	10 % (50)
				28 °C	14	32 % (50)	-	10 % (50)
Culex pipiens molestus	The Netherlands	Lineage 2 (Greece, 2010)	5.7±1.0 × 10^7 TCID50/mL	18 °C	14	24 % (50)	-	6 % (50)	^Citation56
				23 °C	14	24 % (50)	-	10 % (50)
				28 °C	14	14 % (50)	-	10 % (50)
Culex pipiens Hybrid (pipiens x molestus)	The Netherlands	Lineage 2 (Greece, 2010)	5.7±1.0 × 10^7 TCID50/mL	18 °C	14	24 % (50)	-	2 % (50)	^Citation56
				23 °C	14	39 % (50)	-	0 % (50)
				28 °C	14	43 % (50)	-	14 % (50)

Abbreviations: plaque forming units, PFU; tissue culture infectious dose 50, TCID₅₀.

Overview of currently available data on vector competence studies which reported transmission rates of European mosquito species, based on assessment of individual mosquitoes. Only data obtained by natural infection (infectious blood meal) are shown. Infection, dissemination, and transmission rates were calculated as the number of positive samples divided by the total number of tested fed female mosquitoes. Hyphen indicates unknown value.

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