West Nile virus surveillance at a fine scale in an Italian urban ecosystem

doi:10.21203/rs.3.rs-4719836/v1

Download PDF

Research Article

West Nile virus surveillance at a fine scale in an Italian urban ecosystem

https://doi.org/10.21203/rs.3.rs-4719836/v1

This work is licensed under a CC BY 4.0 License

You are reading this latest preprint version

In the last fifteen years, the West Nile virus (WNV) has spread in the Po Valley plain in Italy, extending from Emilia-Romagna to Veneto in Friuli Venezia Giulia, Lombardy, and Piedmont regions. The principal vector of WNV in Italy is Culex pipiens, and lineage 2 of arbovirus can overwinter. The sensitivity of the mosquito surveillance network to the circulation of WNV in urban and rural areas and the impact of the ecological system on the dynamics and spillover of disease were investigated in this study. WNV circulation in mosquitoes collected in 2021–2023 and screened with RT-PCR differed between the two environments. The vector index (VI) was significantly higher for Culex pipiens collected in rural areas and near rural wetlands (VI = 0.08 ± 0.16 SD and VI = 0.15 ± 0.29 SD respectively) than in urban environments (from VI = 0.00 in urban parks to VI = 0.04 ± 0.13SD in peri-urban areas). The incidence of West Nile neuroinvasive disease was higher in rural (1.01 ± 0.59SD per 100.000 inhabitants) than in urban areas (0.43 ± 0.32SD cases per 100.000 inhabitants). Throughout the study duration, by monitoring the virus circulation in mosquitoes, the WNV surveillance in the urban ecosystem predicted spillover in humans with about 2–4 weeks of anticipation, allowing prompt activation of the control protocols defined in the Italian National Plan Surveillance and Control for Arboviruses. WNV circulation in mosquitoes was recorded in urban environments where the probability of the simultaneous presence of reservoirs and vectors was higher such as ecological corridors and peri-urban areas. No WNV circulation was found in mosquitoes in urban parks.

WNV

WNND

Culex pipiens

surveillance

urban ecosystem

Italy

West Nile virus (WNV) is an arbovirus of the family of Flaviviridae (gen. Flavivirus). It is spread by different species of competent ornithophilic mosquito vectors mainly belonging to the genus Culex. Birds are the primary vertebrate WNV reservoirs, while humans and equids are considered dead-end hosts (Bowen & Nemeth 2007). WNV circulation has been observed in several European Union (EU) states since the mid-1950s with irregular fluctuations. In 2018, there was a major outbreak affecting all of Italy, Serbia, Greece and Romania (https://www.ecdc.europa.eu/en/news-events/epidemiological-update-west-nile-virus-transmission-season-europe-2018).

In Italy, WNV is spread by Culex pipiens (Calzolari et al 2015), whose two biotypes have been described (Di Luca 2016) with different behaviours: Cx. p. pipiens is ornithophilic, eurygamous (mates in swarms in open areas) and anautogenous (requires blood meal to lay eggs), and the females overwinter in diapause and live aboveground, while Cx. p. molestus lives preferably in urban areas, has a less specific and partly anthropophilic feeding behaviour, is stenogamous (mates in confined space), autogenous (lays first eggs without blood meal), hypogeous (develops in enclosed habitat) and homodynamic (no diapausing in winter) (Haba and McBride 2022). Sympatric presence of the Cx. pipiens biotypes, especially in peri-urban areas, may lead to hybrids of the two forms with an intermediate behaviour that could be responsible for the passage of the virus from avifauna to humans (Fritz et al 2015 and Tiron et al 2021).

In 2008, the first WNV human infection in the Emilia-Romagna region was registered (Calzolari et al. 2010). Since then, the disease has been considered endemised in the Po Valley (Angelini et al. 2010). The human incidences of West Nile neuroinvasive disease (WNND) (per 100.000 inhabitants) in the Local Health Units (LHUs) of Bologna and the entire Emilia-Romagna region from 2008 to 2023 are shown in Fig. 1. In 2018, a peak viral circulation was reported. This was followed by a sharp decline in 2019 (with zero cases in Bologna LHUs) and subsequent progressive increase in the following years. The trend observed in the Emilia-Romagna region substantially mirrors that of the European Union (Riccò et al 2022).

West Nile disease was first detected in horses in Italy in 1998 in a wetland in Tuscany. The alarm for diffusion in the USA and other parts of Europe and to monitor the possible presence of the virus in Italian wetlands prompted the Italian Ministry of Health to issue the first veterinary surveillance plan in 2002 in fifteen wetlands. In the Emilia-Romagna region in 2008, after several human cases of WNND had been detected, the first surveillance plan for arthropod-borne viral diseases was implemented, providing a diffused entomological surveillance on the territory subject to viral circulation. In 2010, this plan was extended to the Po Valley Plain, including—besides Emilia-Romagna—Veneto, Friuli Venezia Giulia, Lombardy, and Piedmont regions (Bellini et al. 2014). In 2020, the “National Prevention, Surveillance, and Response Plan for Arboviral Diseases (PNA) 2020–2025”, which is coordinated at the national level by the National Institute of Health (ISS) and the Ministry of Health and aims to provide human, veterinary, and entomological surveillance for West Nile virus and implement specific preventive measures and vector control operations, was activated (https://www.epicentro.iss.it/en/west-nile-fever/surveillance).

The surveillance conducted in the Emilia-Romagna region is based on a monitoring network of entomological traps and testing of birds (actively and passively collected) designed to promptly detect viral circulation through PCR screening and activate specific protocols (3 levels of risk), as foreseen in the Regional Plan for Surveillance and Control of Arboviruses (PRA). The PRA provides relevant information to the National Blood and Transplant Centres responsible for screening donor blood, the Local Health Authorities responsible for epidemiological investigation, communication and quality control of mosquito management activities, and the municipalities responsible for mosquito control activities including adult treatment in sensitive areas. The territorial unit considered in the PRA to apply the measures is the province, meaning that when one pool of mosquitoes, one bird, one equine, or one human is found positive the host province is declared affected (https://zanzaratigreonline.it/Media/1618efd2-8264-44c7-b24a-1dcbab961a53/Piano%20Regionale%20Arbovirosi%202023%20.pdf).

Since we have seen usually less WNV circulation in urban areas compared to rural areas (Calzolari et al. 2020), we hypothesised that more sensitive surveillance targeting urban areas could tailor mosquito control activities to real risks of transmission, thus possibly avoiding unnecessary adulticide treatments in urban areas. This study aims to evaluate whether entomological surveillance organised at a fine scale in big cities can promptly detect WNV circulation in urban areas and provide evidence to better modulate vector control interventions, limiting the use of toxic substances to only when necessary. This surveillance would also respond to the need to reduce the risk of WNV circulation in humans and improve the quality of urban environment by minimizing human, animal, and environmental exposure to toxic insecticides while also mitigating the risk of emergence of resistance phenomena that might hurt the effectiveness of extraordinary disinfestation interventions against vectors (Pichler et al 2022).

The study was carried out in the plain area of the Bologna province (1,800 km²) and in the urban area of Bologna (capital province municipality with a surface area of 120 km²) in the years 2021–2023.

Monitoring network – In the Bologna province, we referred to the data collected by the 16 fixed stations of the regional mosquito monitoring network (Fig. 2), two of which are localised in the Bologna peri-urban area and 14 in the province rural areas. The regional entomological monitoring network is organised on 11 x 11 km square grids where one CO₂ trap is activated fortnightly from May to October. In this study, the traps were activated in two main rural environments: around small villages (4 stations) and near wetlands (10 stations). In the Bologna urban area, we specifically activated ten CO₂ traps in parallel with the regional network traps: two in wooded areas near night roosts of corvids, four in the urban river ecological corridor, and four in urban parks (Table 1). This led to more sensitive surveillance in the Bologna urban area (one trap/10 km²) compared to the rural area (one trap/121 km²).

The captured mosquitoes were determined by species, and the females of Cx. pipiens were sorted in a pool consisting of a maximum of 200 individuals, kept in a cold chain, and screened with RT-PCR for the presence of flavivirus (Bellini et al. 2014).

Area under surveillance – The lowland territory of Bologna province is characterised by intensive agriculture, large urbanised area (Bologna city), small towns, and a system of natural areas for the conservation of biodiversity and the protection of plain habitats (mainly different kinds of wetlands such as swamps, ponds, canals and rivers).

The municipality of Bologna includes a hilly wooded area to the south and a highly urbanised flat area crossed by various waterways, which act as ecological corridors, and with various city parks which are refuge and nesting areas for birdlife.

In the winter of 2019–2020, the Association of Ornithologists of Emilia-Romagna (AsOER) observed corvid night roosts in the municipality of Bologna, confirming that hooded crows (Corvus cornix) and jackdaws (Corvus monedula) congregated at sunset to reach the night roosts on foothill sites.

Around 300 to 500 hooded crows were observed in two hilly dormitories near the Ravone stream. The urban population of hooded crows has been estimated at around 1,000 individuals (around 100–200 breeding pairs and 600–800 non-breeding individuals).

In another area near the Savena River, an evening grouping of around 500 jackdaws (Corvus monedula) was observed.

Hooded crows and jackdaws usually roost in fixed tree canopy dormitories outside urban areas. In spring, the adults move to the city to nest and the dormitories are generally frequented only by immatures. In the winter, all exemplars during the day go in search of food in urban areas and, at sunset, return to roost at the dormitories. These dormitories could favour arbovirus survival during the winter months (arbovirus circulation through oral and faecal transmission from bird to bird) and amplification in the vectorial season (Montecino-Latorre and Barker 2018).

In tree canopies, in principal parks in urban areas, and in ecological corridors that cross the city (Reno and Savena rivers and the Navile canal), numerous species of breeding birds were found.

Data on breeding birds found in Bologna province as reported since 2010 on the website www.ornitho.it were analysed and compared to the data reported by Tinarelli and Boldreghini (1998) for monitoring in the period 1980–1996.

Table 1

Mosquito monitoring stations activated in Bologna municipality and province from 2021 to 2023
Network	Municipality	Environment Description	Y	X
RER	Anzola Emilia	Rural area near small country town	44.54704	11.19831
	Baricella	Rural area near wetland	44.67606	11.5659
	Bentivoglio	Rural area near small country town	44.63081	11.4408
	Bologna	Peri-urban area	44.54302	11.2855
	Bologna	Peri-urban area	44.52159	11.40081
	Budrio	Rural area near wetland	44.5658	11.57804
	Budrio	Rural area near small country town	44.49595	11.53245
	Crevalcore	Rural area near wetland	44.71973	11.15646
	Crevalcore	Rural area near wetland	44.79128	11.22266
	Imola	Rural area near wetland	44.48329	11.78259
	Medicina	Rural area near wetland	44.51104	11.70732
	Molinella	Rural area near wetland	44.5694	11.65619
	Mordano	Rural area near wetland	44.42104	11.80085
	Sala Bolognese	Rural area near small country town	44.61023	11.25687
	S.P. in Casale	Rural area near wetland	44.68697	11.41335
	S.G. in P.	Rural area near wetland	44.71753	11.24676
Bologna	Bologna	Ecological corridor	44.49469	11.27986
	Bologna	Urban park	44.48364	11.34884
	Bologna	Urban park	44.51258	11.38868
	Bologna	Urban park	44.50738	11.35254
	Bologna	Ecological corridor	44.50937	11.3325
	Bologna	Ecological corridor	44.53953	11.35174
	Bologna	Peri-urban roost dormitory of C. cornix	44.47496	11.31358
	Bologna	Peri-urban roost dormitory of C. monedula	44.46175	11.38844
	Bologna	Urban park	44.49872	11.38518
	Bologna	Ecological corridor	44.52124	11.29925

Statistical analysis – All the analyses were performed using the R programming language (R Core Team). Since the monitoring and vector index (VI) data were not in normality (tested using the Shapiro–Wilk test), non-parametric ANOVA (Kruskal–Wallis) was performed. The differences between environments were investigated using the Dwass–Steel–Critchlow–Fligner (DSCF) test for multiple comparison analysis.

The WNV infection rate and the VI were estimated using the maximal likelihood estimation (MLE) of infection data collected during the circulation period (week 25–41) of each environment by means of the PooledInfRate 4.0 software (Biggerstaff 2009)

Diversity studies of mosquito species were conducted separately for each environment by calculating the classic species richness Shannon indices, diversity (\(\:H=\sum\:_{i=1}^{S}{p}_{i}\text{*}\text{log}{p}_{i}\:)\:\)and evenness (\(\:J=\frac{H}{\text{log}S}\))

In human patients with WNND, the WNV RNA was detected in the plasma, serum, and cerebrospinal fluid samples (CSF), and performed by RT-PCR methods (Bellini et al. 2014).

In the three-year study, 244,036 mosquito females of 13 species and five genera were caught.

The mosquito species diversity (H) in the agro ecosystem (H = 0.57 ± 0.28, J = 0.77 ± 0.35) was significantly higher (Tab. S1) than in the urban ecosystem (H = 0.41 ± 0.30, J = 0.68 ± 0.53), and no differences in evenness (J) was found in any environment. The dominant species in all the environments was Cx. pipiens, representing 83–98% of total mosquito collections. In addition to Cx. pipiens, Aedes albopictus, a species typical of metropolitan areas in Italy and representing 5–12% of total mosquito collections in this study, was collected in urban and peri-urban areas. In the rural areas, especially near wetlands, Aedes caspius and Aedes vexans, representing 12–13% of total mosquitoes collected, were caught especially after the 2022 flood.

In Bologna municipality, no significant differences in diversity and evenness indices between the monitoring environments were recorded (Tab. S2). However, a greater number of species were found in the peri-urban monitoring sites, where the Shannon indices were higher (Tab. S3).

The pie charts of the faunistic composition of Culicidae collected in different environments are shown in Fig. 3.

The microclimate was significantly different in the two ecosystems: a higher average yearly temperature (+ 1.4°C) and lower relative humidity (RH) (-7.9%) were observed in the urban areas compared to the rural areas, while the differences in rainfall were very low (on average + 9% in the urban areas) (Tab. S4).

Data from www.ornitho.it indicate 88 breeding bird species for the Bologna conurbation in 2010–2023, some of which are considered confirmed, probable, or possibly nesting species. This is a significant increase compared to the 65 species found in 1980–1996 (Tinarelli and Boldreghini 1998). The increase occurred all over the province but particularly in the urban areas around the historic centre (+ 65%; 28 new and 4 disappeared species) due to the presence of small wetlands, settlement of birds of prey, and strengthening and maturation of areas with trees and shrubs. The hooded crow (Corvus cornix), which was present in a few pairs in 1980–1996, and the collared parakeet (Psittacula krameri) and the wood pigeon (Columba palumbus), which were previously absent, have colonised the entire territory of the conurbation in recent years with a significant increase in their populations. The dominant species in Bologna urban areas nowadays are the Columbus, the collared dove, the wood pigeon, the blackbird, the starling, and the hooded crow (S5).

Table 2

Number of *Cx. pipiens* females (*Cx. p.*) caught by the traps and pools analysed with RT-PCR flavivirus analysis
Year	Environment monitored	No. of pools of Cx. p.	No. of Cx. p. analysed
2021	Urban ecological corridor	23	561
	Peri-urban near rural area	24	1080
	Peri-urban near corvid roost dormitory	8	137
	Urban park	35	513
	Rural area near small country town	54	4142
	Rural area near wetland	150	18596
	Total 2021	294	25029
2022	Urban ecological corridor	39	1031
	Peri-urban near rural area	22	946
	Peri-urban near corvid roost dormitory	22	247
	Urban park	43	1395
	Rural area near small country town	53	3949
	Rural area near wetland	141	14817
	Total 2022	320	22385
2023	Urban ecological corridor	93	11595
	Peri-urban near rural area	56	7884
	Peri-urban near corvid roost dormitory	29	3049
	Urban park	58	4073
	Rural area near small country town	140	22268
	Rural area near wetland	395	64817
	Total 2023	771	113686
Grand Total		1385	161,100

The RT-PCR flavivirus analysis of 161,100 Cx. pipiens females sorted and pooled in 1385 samples (made up of a maximum of 200 females each) was conducted in the three years of the study (Table 2). Thirty-nine pools tested positive for WNV for lineage 2 (2.82%) and only one for lineage 1 (0.07%).

The Kruskal–Wallis analysis of the number of Cx. pipiens females, infection rates, and vector indices showed significant differences (Table 3e 4) between the six monitored environments. All three parameters were higher in stations activated in rural areas (especially in wet environments) than in those activated in urban areas (mostly those activated in urban parks and ecological corridors). Compared to the rural areas, no statistically significant differences in WNV circulation were observed in the urban ecosystem, but the lowest vector index (VI) and a minor density of Cx. pipiens females were found in urban parks and peri-urban hilly corvid canopy roost areas.

Table 3

Kruskal–Wallis analysis of the number of females collected, infection rates (IR) and vector indices (VI)
Parameters	χ²	Gdl	p
Females	45.52	5	< .001
IR	30.12	5	< .001
VI	30.51	5	< .001

Table 4

Average number of females collected, infection rates (IR) and vector indices (VI) and Dwass–Steel–Critchlow–Fligner (DSCF) pairwise comparisons (*different letters indicate statistically significant differences, p < 0.05)
Parameters	Area	N	Mean	SD	DSCF*
Females	Urban ecological corridor	24	97.16	305.32	ac
	Peri-urban	24	164.25	478.52	ac
	Peri-Urban hilly roost	21	61.40	166.84	b
	Urban park	24	39.10	82.12	ab
	Rural	24	157.90	346.49	cd
	Rural near wetland	24	190.30	269.64	d
IR	Urban ecological corridor	24	0.0006	0.0023	a
	Peri-urban	24	0.0024	0.0101	a
	Peri-urban hilly roost	21	0.0001	0.0003	a
	Urban park	24	0.0000	0.0000	a
	Rural	24	0.0015	0.0030	ab
	Rural near wetland	24	0.0012	0.0018	b
VI	Urban ecological corridor	24	0.0215	0.0727	a
	Peri-urban	24	0.0388	0.1317	a
	Urban hilly roost	21	0.0235	0.1079	a
	Urban park	24	0.0000	0.0000	a
	Rural	24	0.0818	0.1569	ab
	Rural near wetland	24	0.1484	0.2899	b

In the three years of the study, 32 confirmed human infections were officially reported, including 24 WNND cases, 2 West Nile fever (WNF) cases, and 6 asymptomatic infections among blood donors (WNI). To guarantee uniformity, only WNND cases were considered in the analysis (Table 5).

Table 5

Human WNV (WNI, WNF and WNND) cases recorded in Bologna province in the period 2021–2023
Year	WNV	Age	Sex	Municipality	Date of initial symptoms
2021	WNND	47	M	Anzola dell'Emilia	31 Jul
	WNND	80	M	Medicina	01 Aug
2022	WNND	73	M	Imola	20 Jul
	WNND	58	F	Valsamoggia	29Jul
	WNND	47	F	Minerbio	01 Aug
	WNI	47	M	Castel Guelfo di Bologna	3 Aug
	WNND	77	M	Bologna	4 Aug
	WNI	59	M	Imola	16 Aug
	WNND	72	M	Mordano	20 Aug
	WNND	56	M	Castel Guelfo di Bologna	28 Aug
	WNND	70	F	Bologna	02 Sep
	WNI	50	M	Budrio	06 Sep
	WNF	78	F	Valsamoggia	15 Sep
	WNND	64	F	Galliera	08 Oct
	WNF	72	M	Minerbio	09 Oct
2023	WNND	87	M	Bologna	23 Jul
	WNND	44	F	Medicina	30 Jul
	WNND	87	F	Argelato	01 Aug
	WNND	53	M	Bologna	01 Aug
	WNND	56	M	Medicina	05 Aug
	WNND	90	M	Bologna	07 Aug
	WNI	45	M	Crevalcore	07 Aug
	WNI	47	M	Granarolo dell'Emilia	20 Aug
	WNND	59	F	Budrio	23 Aug
	WNND	65	M	Medicina	24 Aug
	WNND	76	F	Minerbio	28 Aug
	WNND	77	F	Imola	29 Aug
	WNND	68	F	Sala Bolognese	02 Sep
	WNND	71	M	Imola	02 Sep
	WNND	86	F	Sala Bolognese	10 Sep
	WNND	84	M	Castenaso	11 Sep
	WNI	50	M	Granarolo dell'Emilia	13 Oct

In 2021, a high WNV circulation was observed in mosquitoes collected in early August in rural environments near wetlands, while no and low circulation were observed in urban and rural areas respectively (only two WNND cases were observed in the rural area on 31 July and 1 August, i.e. in week 31).

In 2022, WNV circulation in mosquitoes was recorded only in peri-urban and rural and wetlands in weeks 29 and 30, while the WNND cases were observed from 20 July (week 30) in rural areas and from 1 August (week 32) in urban areas.

In 2023, mosquito pools were infected in all environments monitored, except in urban parks. WNV circulation in mosquitoes started in week 26 up to week 27 in rural areas and in week 28 up to week 29 in urban areas. In urban and rural areas, the first human circulation was observed on 23 July (week 30) and 30 July (week 31) respectively (Fig. 4).

Table 6

Surveillance data recorded in urban and rural areas of Bologna province from 2021 to 2023.
Years	Area	WNND		WNV circulation
		No. cases	Incidence per 100,000 inh.	Cx. pipiens
		No. cases	Incidence per 100,000 inh.	Pool No.	Pool +	%pool +	VI Average 25–41 w	VI Max
2021	Urban	0	0.00	90	0	0.00%	0.00	0.00
2021	Rural	2	0.20	205	11	5.37%	0.12	1.37
2022	Urban	2	0.51	126	1	0.79%	0.01	0.44
2022	Rural	6	0.59	194	6	3.09%	0.06	0.25
2023	Urban	3	0.77	236	4	1.69%	0.05	0.49
2023	Rural	11	1.08	536	18	3.36%	0.17	0.57

The WNND incidence was higher in rural areas than in urban areas (on average 1.01 ± 0.59SD and 0.43 ± 0.32SD cases per 100,000 inh. respectively), and differences were observed in the VI values (VI = 0.12 ± 0.04 SD and VI = 0.02 ± 0.02SD respectively), showing a higher risk in rural areas (Table 6).

A complex, though not clearly elucidated, interrelationship between ecological and environmental factors on vectors and host populations influences the dynamics of WNV transmission in humans, particularly in urban environment (Giesen et al. 2022). The interaction between weather, environmental factors, virus reservoirs, and vector mosquitoes maintains an enzootic transmission cycle of WNV.

Land urbanization and Cx. pipiens hybrid biotypes with opportunistic blood-feeding behaviour favour human infection.

WNV has been detected in Bologna province in 13 different species of wild birds dead and 3 resident birds of target species (Pica pica, Corvus corone cornix and Garrulus glandarius) collected from 2021 to 2023

(https://westnile.izs.it/j6_wnd/home_en;jsessionid=9027A8B3F1E8FCE308ACEDDA0CC8F2CE). The bird species have different potentials for WNV transmission and the relevance of the composition of bird communities in the circulation of the virus (e.g. dilution effect) has been hypothesised. Research to identify the primary amplifiers of the virus that influence circulation locally in Italy is still in progress.

The policies promoted by Bologna municipality and Emilia-Romagna region regarding the increase in biodiversity in urban environment may play a positive role in amplifying hosts, since the increased relevance of less competent bird host species and the composition of bird communities could affect WNV circulation (Swaddle & Calos 2008 and Allan et al. 2009).

WNV circulation in mosquitoes occurred from weeks 26 to 30 (ending of June to mid-July), and the onset of WNND cases happened in weeks 30 and 31 (second half of July).

In rural areas, WNV circulation preceded the WNND cases in two out of the three years (2021 and 2023), while both events overlapped in one year (2022). In Bologna city, the virus circulation in mosquitoes always precedes the clinical manifestation of WNND by at least two weeks, as already observed by Bellini et al. 2014. These differences between the rural and urban areas may be linked to the different densities of the traps; indeed, the trap density in urban areas was ten times higher.

In the 2021 season, there was a high WNV circulation in the mosquito population collected near the wetlands, but the incidence of WNV in human beings was very low. This phenomenon might be tied up to the concentration of birds and mosquitoes, especially Ardeidae and Anatidae, in the wetlands.

In the urban areas of Bologna, a WNV circulation in mosquitoes was recorded in environments where the probability of the simultaneous presence of bird reservoirs and vectors was higher.

The mosquito density and WNV circulation were higher in peri-urban areas and ecological corridors than in urban parks in all the sampling periods.

Approximately 80% of human WNV infections are asymptomatic, and less than one percent may cause WNND (https://www.ecdc.europa.eu/en/west-nile-virus-infection). These infections do not seem to be strongly correlated with VI and mosquito density, indicating that different factors may contribute to WNV seasonal spillover in humans, which remains a random event difficult to quantify especially at a fine territorial scale.

It is difficult to understand how climate change will impact the complex vector–host–pathogen system and how the virus in human transmission in urban areas will evolve in the coming years. Increased temperature will have direct and indirect impacts on vectors and hosts, an example of this effect was observed in 2018 when the intensification of WNV transmission in Italy appeared to be linked to high temperatures recorded during spring, in the period nesting of different bird species (Marini et al. 2020).

A good understanding of changes in urban environment ecology, WNV circulation, correct prevention strategies through the implementation of larvicidal (all over Bologna territory) and adulticidal (in localised areas where the risks of arbovirus circulation are higher) control programs, and how to protect fragile human subjects will be fundamental to reducing WNV incidence in the future and safeguarding the urban environment.

The WNV circulation in urban ecosystems appears to be lower than in rural and wetland areas. The surveillance network activated (one trap per 10 km²) in Bologna city in our study seemed sufficiently sensitive to detect WNV circulation, predict spillover, and allow competent authorities to promptly activate the PRA protocols for WNV control.

Mosquito monitoring in sensitive urban areas, where the simultaneous presence of vectors and WNV reservoirs is more likely, showed no evidence of greater WNV circulation in Cx. pipiens. Given the ability of reservoirs and vectors to move even over long distances, it might be hazardous to differentiate the mosquito control activities in urban areas depending on the positivity recorded in the monitoring network. The implementation of prevention measures in urban environments is advisable and, in the case of WNV circulation, extraordinary interventions must be started in sites where people are WNND-susceptible (elderly, chronically ill, and immunocompromised) or in areas where they occur in the evenings.

We must expect the mutation of the WNV enzootic cycle and the human spillover influenced by climate change in the coming years, and the monitoring of such spillover will be crucial to prevent possible WNV outbreaks.

Data used in this study was collected in the “Regional Surveillance of Arboviral Diseases” project, financed by the Emilia-Romagna Region.

The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

The authors have no relevant financial or non-financial interests to disclose.

Author contribution

All authors contributed to the study conception and design.

P. Angelini, G. Matteo, A. Puggioli, M. Dottori, M.Calzolari, D. Torri, and A. Grisendi performed the laboratory work. M. Carrieri collected mosquitoes in the field, analysed the data and wrote the first draft of the manuscript. R. Tinarelli performed analysed bird lives. All authors discussed the results and approved the final version of the manuscript.

Acknowledgement

Data were obtained from the Regional Plan for Arboviruses Surveillance and Control of Emilia-Romagna Region.The scientific work was partially financed by IZSLER.We would like to thank Mario Marinozzi and Teresa Brandolini for assistance with the field and identification work as well as the laboratory work, and ARPAE Emilia-Romagna for providing meteorological data.

Allan BF, Langerhans RB, Ryberg WA, Landesman WJ, Griffin NW, Katz RS, Oberle BJ, Schutzenhofer MR, Smyth KN, de St Maurice A, Clark L, Crooks KR, Hernandez DE, McLean RG, Ostfeld RS, Chase JM. Ecological correlates of risk and incidence of West Nile virus in the United States. Oecologia. 2009 Jan;158(4):699-708. doi: 10.1007/s00442-008-1169-9. Epub 2008 Oct 22. PMID: 18941794.
Angelini P, Tamba M, Finarelli AC, Bellini R, Albieri A, Bonilauri P, Cavrini F, Dottori M, Gaibani P, Martini E, Mattivi A, Pierro AM, Rugna G, Sambri V, Squintani G, Macini P. West Nile virus circulation in Emilia-Romagna, Italy: the integrated surveillance system 2009. Euro Surveill. 2010 Apr 22;15(16):19547. PMID: 20430000.
Bellini R, Calzolari M, Mattivi A, Tamba M, Angelini P, Bonilauri P, Albieri A, Cagarelli R, Carrieri M, Dottori M, Finarelli AC, Gaibani P, Landini MP, Natalini S, Pascarelli N, Rossini G, Velati C, Vocale C, Bedeschi E. The experience of West Nile virus integrated surveillance system in the Emilia-Romagna region: five years of implementation, Italy, 2009 to 2013. Euro Surveill. 2014 Nov 6;19(44):20953. doi: 10.2807/1560-7917.es2014.19.44.20953. PMID: 25394257.
Biggerstaff BJ. PooledInfRate, Version 4.0: a Microsoft Office Excel Add-In to compute prevalence estimates from pooled samples. 2009. Atlanta: Center for Disease Control and Prevention.
Bowen RA, Nemeth NM. Experimental infections with West Nile virus. Curr Opin Infect Dis. 2007 Jun;20(3):293-7. doi: 10.1097/QCO.0b013e32816b5cad. PMID: 17471040.
Calzolari M, Bonilauri P, Bellini R, Caimi M, Defilippo F, Maioli G, Albieri A, Medici A, Veronesi R, Pilani R, Gelati A, Angelini P, Parco V, Fabbi M, Barbieri I, Lelli D, Lavazza A, Cordioli P, Dottori M. Arboviral survey of mosquitoes in two northern Italian regions in 2007 and 2008. Vector Borne Zoonotic Dis. 2010 Nov;10(9):875-84. doi: 10.1089/vbz.2009.0176. Epub 2010 Apr 6. PMID: 20370434.
Calzolari M, Pautasso A, Montarsi F, Albieri A, Bellini R, Bonilauri P, Defilippo F, Lelli D, Moreno A, Chiari M, Tamba M, Zanoni M, Varisco G, Bertolini S, Modesto P, Radaelli MC, Iulini B, Prearo M, Ravagnan S, Cazzin S, Mulatti P, Monne I, Bonfanti L, Marangon S, Goffredo M, Savini G, Martini S, Mosca A, Farioli M, Gemma Brenzoni L, Palei M, Russo F, Natalini S, Angelini P, Casalone C, Dottori M, Capelli G. West Nile Virus Surveillance in 2013 via Mosquito Screening in Northern Italy and the Influence of Weather on Virus Circulation. PLoS One. 2015 Oct 21;10(10):e0140915. doi: 10.1371/journal.pone.0140915. Erratum in: PLoS One. 2015;10(12):e0146436. PMID: 26488475; PMCID: PMC4619062.
Calzolari M, Angelini P, Bolzoni L, Bonilauri P, Cagarelli R, Canziani S, Cereda D, Cerioli MP, Chiari M, Galletti G, Moirano G, Tamba M, Torri D, Trogu T, Albieri A, Bellini R, Lelli D. Enhanced West Nile Virus Circulation in the Emilia-Romagna and Lombardy Regions (Northern Italy) in 2018 Detected by Entomological Surveillance. Front Vet Sci. 2020 May 5;7:243. doi: 10.3389/fvets.2020.00243. PMID: 32432132; PMCID: PMC7214930.
Di Luca M, Toma L, Boccolini D, Severini F, La Rosa G, Minelli G, Bongiorno G, Montarsi F, Arnoldi D, Capelli G, Rizzoli A, Romi R. Ecological Distribution and CQ11 Genetic Structure of Culex pipiens Complex (Diptera: Culicidae) in Italy. PLoS One. 2016 Jan 7;11(1):e0146476. doi: 10.1371/journal.pone.0146476. PMID: 26741494; PMCID: PMC4712155.
Fritz ML, Walker ED, Miller JR, Severson DW, Dworkin I. Divergent host preferences of above- and below-ground Culex pipiens mosquitoes and their hybrid offspring. Med Vet Entomol. 2015 Jun;29(2):115-23. doi: 10.1111/mve.12096. Epub 2015 Jan 20. PMID: 25600086.
Giesen C, Herrador Z, Fernandez-Martinez B, Figuerola J, Gangoso L, Vazquez A, Gómez-Barroso D. A systematic review of environmental factors related to WNV circulation in European and Mediterranean countries. One Health. 2023 Jan 6;16:100478. doi: 10.1016/j.onehlt.2022.100478. PMID: 37363246; PMCID: PMC10288031.
Haba Y, McBride L. Origin and status of Culex pipiens mosquito ecotypes. Curr Biol. 2022 Mar 14;32(5):R237-R246. doi: 10.1016/j.cub.2022.01.062. PMID: 35290776; PMCID: PMC9108678.
Marini G, Calzolari M, Angelini P, Bellini R, Bellini S, Bolzoni L, Torri D, Defilippo F, Dorigatti I, Nikolay B, Pugliese A, Rosà R, Tamba M. A quantitative comparison of West Nile virus incidence from 2013 to 2018 in Emilia-Romagna, Italy. PLoS Negl Trop Dis. 2020 Jan 2;14(1):e0007953. doi: 10.1371/journal.pntd.0007953.
Meschini E. & F. Rugis S. 1993 – Atlante Degli Uccelli Nidificanti In Italia. Suppl. Ric. Biol. Selvaggina, 20: 1-334
Montecino-Latorre D, Barker CM. Overwintering of West Nile virus in a bird community with a communal crow roost. Sci Rep. 2018 Apr 17;8(1):6088. doi: 10.1038/s41598-018-24133-4. PMID: 29666401; PMCID: PMC5904116.
Pichler V, Giammarioli C, Bellini R, Veronesi R, Arnoldi D, Rizzoli A, Lia RP, Otranto D, Ballardini M, Cobre P, Serini P, Della Torre A, Caputo B. First evidence of pyrethroid resistance in Italian populations of West Nile virus vector Culex pipiens. Med Vet Entomol. 2022 Sep;36(3):390-395. doi: 10.1111/mve.12573. Epub 2022 Apr 9. PMID: 35396754; PMCID: PMC9540436.
Riccò M, Peruzzi S, Balzarini F. Epidemiology of West Nile Virus Infections in Humans, Italy, 2012-2020: A Summary of Available Evidences. Trop Med Infect Dis. 2021 Apr 24;6(2):61. doi: 10.3390/tropicalmed6020061. PMID: 33923347; PMCID: PMC8167603.
Swaddle JP, Calos SE. Increased avian diversity is associated with lower incidence of human West Nile infection: observation of the dilution effect. PLoS One. 2008 Jun 25;3(6):e2488. doi: 10.1371/journal.pone.0002488. PMID: 18575599; PMCID: PMC2427181.
Tinarelli R. & Boldreghini P. Avifauna nidificante nella conurbazione Bolognese. 1998. In: Bologna M.A., Carpaneto G.M., Cignini B. (eds.) – Proceedings of 1° Convegno Nazionale sulla Fauna Urbana: 147-150. Fratelli Palombi Editori.
Tinarelli R. Autunno dell’anno 2000: crollo improvviso delle popolazioni di Passera d’italia e Passera mattugia in diverse località dell’Emilia-Romagna. 2009. Convegno internazionale. Passeri in crisi ? Pisa 2009, Ecologia Urbana - 21 (1) 2009: 72-76.
Tiron GV, Stancu IG, Dinu S, Prioteasa FL, Fălcuță E, Ceianu CS, Cotar AI. Characterization and Host-Feeding Patterns of Culex pipiens s.l. Taxa in a West Nile Virus-Endemic Area in Southeastern Romania. Vector Borne Zoonotic Dis. 2021 Sep;21(9):713-719. doi: 10.1089/vbz.2020.2739. Epub 2021 Jun 22. PMID: 34160283.

No competing interests reported.

Supplementary.docx

Download PDF

Editor assigned by journal
11 Jul, 2024
Submission checks completed at journal
11 Jul, 2024
First submitted to journal
10 Jul, 2024

You are reading this latest preprint version

West Nile virus surveillance at a fine scale in an Italian urban ecosystem

Status:

Version 1

Abstract

Figures

Introduction

Materials and Methods

Results

Discussion

Conclusion

Declarations

Acknowledgement

References

Additional Declarations

Supplementary Files

Status:

Version 1