Susceptibility of wild and domestic #songbirds to #Usutu virus

Abstract

Usutu virus (USUV) is an emerging mosquito-borne orthoflavivirus that can cause neuroinvasive disease in humans and wild birds. USUV clusters phylogenetically within the Japanese encephalitis virus serocomplex, sharing antigenic and ecological similarity with West Nile virus (WNV). USUV is maintained in an enzootic cycle primarily involving passerine birds and Culex spp. mosquitoes. USUV was first isolated in South Africa in 1959 and has since spread throughout Africa and Europe, causing mortality and disease in several wild bird populations, specifically the Eurasian blackbird (Turdus merula). To understand transmission and pathogenesis of USUV in birds, we sought to develop passerine bird models of infection using wild-caught house finches (Haemorhous mexicanus), wild-caught American robins (Turdus migratorius), domestic canaries (Serinus canaria domestica), and captive-bred zebra finches (Taeniopygia guttata). Birds were inoculated with one or two isolates of USUV and viremia was measured. House finches, American robins, and canaries were susceptible to USUV, with 100% of inoculated birds developing viremia. These avian species reach viremias that have the potential to infect Cx. quinquefasciatus mosquitoes. Clinical disease and histopathological evidence of disease were severe in American robins and moderate to severe in canaries, with limited disease in house finches. However, zebra finches inoculated with one isolate of USUV did not develop detectable viremia. These findings provide additional tools for studying USUV enzootic transmission and pathogenesis in passerine birds.

Source: 

Link: https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014213

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#Italy, #WNV & #USUV Integrated #Surveillance - Weekly Bulletin No. 16 - 30 October 2025 (Summary)

 

{Summary}

-- During current epidemiological week (from 23 to 29 Oct. 2025), two new human cases of infection with West Nile Virus have been reported. 

-- The cumulative number of confirmed cases this season so far rose to 773 (they were 771 last week), of these: 

- 367 were West Nile Neuroinvasive Disease (WNND): 17 in Piedmont, 56 Lombardy, 35 Veneto, 4 Friuli-Venezia Giulia, 1 Liguria, 30 Emilia-Romagna, 11 Tuscany, 1 Marche, 87 Latium, 2 Molise, 83 Campania, 2 Apulia, 2 Basilicata, 5 Calabria, 3 Sicily, 28 Sardinia, 

- 56 were asymptomatic cases detected in blood donors, 

- 339 were West Nile Fever cases (of which: 1 imported from Kenya, 1  from Egypt and 1 from Maldives), 

- 3 asymptomatic cases, 

- 8 unspecified cases. 

-- Among confirmed cases, 72 fatalities have been recorded: 7 in Piedmont, 9 Lombardy, 1 Veneto, 2 Emilia-Romagna, 1 Marche, 19 Latium, 29 Campania, 2 Calabria, 1 Sicily, 1 Sardinia. 

- The Case-Fatality Rate in WNND cases is 19.6% (it was 20% in 2018, 14% in 2024). 

-- Since the start of the epidemic season, 11 confirmed human cases of Usutu virus infection were reported: 2 in Piedmont, 3 Lombardy, 2 Veneto, 1 Tuscany, 3 Latium.

(...)

Source: High Institute of Health, https://www.epicentro.iss.it/westnile/bollettino/Bollettino_WND_2025_16.pdf

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Detection of #WNV, #USUV and #Insect-Specific #Bunyaviruses in #Culex spp. Mosquitoes, #Greece, 2024

 

Abstract

Greece is one of the countries in Europe most affected by West Nile virus (WNV), and since 2010, when the virus caused a large outbreak with 197 human neuroinvasive cases, outbreaks occur almost every year. Mosquito surveillance is an indirect sign of virus circulation; therefore, the purpose of the study was the molecular detection of WNV in 45,988 C. pipiens s.l. mosquitoes collected during 2024 in four Regions of Greece and the genetic characterization of the virus strains. WNV was detected in 41 of 1316 (3.12%) Culex spp. mosquito pools. Next-generation sequencing was applied to the WNV-positive samples that had a high viral load. All WNV sequences belong to Cluster B of the sub-lineage Europe WNV-2A presenting a temporal clustering. The WNV infection rates varied highly across the Regions, regional units and months, being higher in Thessaly and Central Macedonia Regions, especially in July and September. All mosquito pools were also tested for Usutu virus (USUV), and one pool was found positive, with sequence clustering into the EU-2 lineage. A subset of mosquitoes (737 pools) was tested for additional viruses, and bunya-like viruses were detected in 6 pools with sequences clustering into four distinct subclades. The prompt detection of pathogenic viruses is helpful for the design of control measures, while the detection of insect-specific viruses provides insights into viral diversity and evolution.

Source: Viruses, https://www.mdpi.com/1999-4915/17/11/1414

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#Italy, #WNV & #USUV Integrated #Surveillance - Weekly Bulletin No. 14, 15 Ocotber 2025 (ISS, edited)

 

{Summary}

-- New human cases of West Nile Virus infection continue to be reported albeit with reduced intensity. 

-- During current epidemiological week (from 9 to 15 October 2025) 26 new confirmed cases have been reported. 

-- The total number of cases so far is 767 (they were 740 last week), of these: 

- 366 were West Nile Neuroinvasive Disease (WNND): 17 in Piedmont, 56 Lombardy, 34 Veneto, 4 Friuli-Venezia Giulia, 1 Liguria, 32 Emilia-Romagna, 10 Tuscany, 1 Marche, 86 Latium, 2 Molise, 83 Campania, 2 Apulia, 2 Basilicata, 5 Calabria, 3 Sicily, 28 Sardinia, 

- 57 were asymptomatic cases among blood donors, 

- 333 were West Nile Fever cases (of which 1 imported from Kenya, 1 from Egypt and 1 from Maldive), 

- 3 asymptomatic cases, 

- eight unspecified cases. 

-- Among confirmed cases, 69 fatalities have been reported: 7 in Piedmont, 9 Lombardy, 2 Emilia-Romagna, 18 Latium, 29 Campania, 2 Calabria, 1 Sicily, 1 Sardinia. 

-- The case-fatality rate in WNND cases stands at 18.8% (in 2018 it was 20%, in 2024 it was 14%). 

-- So far this season, 10 cases of Usutu virus infection have been recorded: 2 in Piedmont, 3 Lombardy, 2 Veneto, 3 Latium.

(...)

Source: High Institute of Health, https://www.epicentro.iss.it/westnile/bollettino/Bollettino_WND_2025_14.pdf

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#Italy, Integrated #WNV & #USUV #Surveillance - Weekly Bulletin No. 13, 9 October 2025 (Summary): 22 new confirmed cases

{Summary}

-- During current epidemiological week, a rise in the West Nile Virus human cases has been observed although with reduced intensity compared most recent weeks. 

-- Twenty-two new confirmed human cases have been reported during surveillance week from 2 to 8 October 2025. 

-- The cumulative number of cases rose to 740 (they were 718 last week), of these: 

- 354 were West Nile Neuroinvasive Disease (WNND): 16 in Piedmont, 53 Lombardy, 33 Veneto, 4 Friuli-Venezia Giulia, 1 Liguria, 30 Emilia-Romagna, 11 Tuscany, 1 Marche, 84 Latium, 2 Molise, 81 Campania, 2 Apulia, 2 Basilicata, 5 Calabria, 3 Sicily, 26 Sardinia,

- 57 were asymptomatic cases in blood donors, 

- 318 were West Nile Fever cases, of which 1 imported from Kenya, 1 from Egypt and 1 from Maldives, 

- 4 asymptomatic cases, 

- 7 unspecified cases. 

-- Among confirmed cases there were 68 fatalities: 7 in Piedmont, 9 Lombardy, 2 Emilia-Romagna, 18 Latium, 28 Campania, 2 Calabria, 1 Sicily, 1 Sardinia. 

- The Case-Fatality Rate in WNND cases is now at 19.2% (it was 20% in 2018 and 14% in 2024). 

-- During current epidemic season, ten Usutu Virus human cases have been confirmed: 2 in Piedmont, 3 Lombardy, 2 Veneto, 3 Latium.

(...)

Source: High Institute of Health, https://www.epicentro.iss.it/westnile/bollettino/Bollettino_WND_2025_13.pdf

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#Italy, Integrated #WNV & #USUV #Surveillance - Weekly Bulletin No. 12, 2 October 2025: 38 new confirmed cases (Summary)

 

{Summary}

-- During current epidemiological week (from 25 September to 1rst October 2025), 38 new confirmed human infection with West Nile Virus have been reported. 

-- Since the beginning of the epidemic season, 718 confirmed cases have been recorded in Italy (they were 680 in the last bulletin), of these: 

- 341 were West Nile Neuroinvasive Disease (WNND): 15 in Piedmont, 51 Lombardy, 30 Veneto, 4 Friuli-Venezia Giulia, 1 Liguria, 27 Emilia-Romagna, 11 Tuscany, 1 Marche, 84 Latium, 2 Molise, 79 Campania, 2 Apulia, 2 Basilicata, 5 Calabria, 2 Sicily, 25 Sardinia, 

- 57 were asymptomatic cases in blood donors, 

- 309 were West Nile Fever cases (1 imported from Kenya, 1 Egypt, and one Maldives), 

- 4 asymptomatic cases, 

- 7 unspecified cases. 

-- Among confirmed cases, there have been 49 fatalities: 7 in Piedmont, 5 Lombardy, 2 Emilia-Romagna, 18 Latium, 14 Campania, 2 Calabria, 1 Sardinia. 

- The Case-Fatality Rate in WNND cases was 14.4% (it was 20% in 2018 and 14% in 2024. 

-- This season 10 confirmed Usutu virus human infections have been recorded: 2 in Piedmont, 3 Lombardy, 2 Veneto, 3 Latium.

(...)

Source: High Institute of Health, https://www.epicentro.iss.it/westnile/bollettino/Bollettino_WND_2025_12.pdf

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#Italy, Integrated #WNV & #USUV #Surveillance - Weekly Bulletin No. 11, September 25 '25 (ISS, Summary)

 

{Summary}

-- During current surveillance week (from 18 to 24 Sept. '25), 33 new confirmed human cases of West Nile Virus have been detected. 

-- Since the beginning of the epidemic season, there have been 680 cases in total, (they were 647 last week); of these: 

- 321 were West Nile Neuroinvasive Disease (WNND): 15 in Piedmont, 44 Lombardy, 27 Veneto, 2 Friuli-Venezia Giulia, 1 Liguria, 25 Emilia-Romagna, 8 Tuscany, 1 Marche, 83 Latium, 2 Molise, 79 Campania, 2 Apulia, 2 Basilicata, 5 Calabria, 1 Sicily, 24 Sardinia), 

- 54 were asymptomatic cases in blood donors, 

- 296 were West Nile Fever cases (1 imported from Kenya, 1 Egypt and 1 Maldives), 

- 3 asymptomatic cases,  

- 6 unspecified cases. 

-- Among confirmed cases, there were 48 deaths: 7 in Piedmont, 5 Lombardy, 2 Emilia-Romagna, 17 Latium, 14 Campania, 2 Calabria, 1 Sardinia. 

- The Case-Fatality Rate among WNND cases was 14.9% (it was 20% in 2018 and 14% in 2024). 

-- During current surveillance week, nine new confirmed human cases of Usutu virus have been confirmed: 2 in Piedmont, 2 Lombardy, 2 Veneto, 3 Latium).

(...)

Source: High Institute of Health, https://www.epicentro.iss.it/westnile/bollettino/Bollettino_WND_2025_11.pdf

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#Italy, Integrated #Surveillance for #WNV & #USUV - Weekly Bulletin No. 10, 18 September '25 (Summary)

 

{Summary}

-- During current epidemiological week (11– 17 September 2025), 65 new confirmed human cases of infection with West Nile Virus have been reported. 

-- The total number of confirmed cases, since the beginning of the epidemic season, has thus risen to 647 (it was 582 last week), of these: 

- 300 were West Nile Neuroinvasive Disease (WNND): 15 in Piedmont, 39 Lombardy, 24 Veneto, 2 Friuli-Venezia Giulia, 1 Liguria, 23 Emilia-Romagna, 5 Tuscany, 83 Latium, 2 Molise, 77 Campania, 2 Apulia, 2 Basilicata, 5 Calabria, 1 Sicily, 19 Sardinia, 

- 54 were asymptomatic cases detected among blood donors, 

- 284 were West Nile Fever cases (one imported from Kenya), 

- 3 asymptomatic cases and 

- 6 unspecified casese. 

-- Among confirmed cases, there were 47 death cases: 7 in Piedmont, 5 Lombardy, 1 Emilia-Romagna, 16 Latium, 15 Campania, 2 Calabria, 1 Sardinia. 

- The Case-Fatality Rate in WNND cases was 15.8% (it was 20% in 2018 and  14% in 2024). 

-- This week nine confirmed cases of Usutu Virus infection have been reported: 2 in Piedmont, 2 Lombardy, 2 Veneto, 3 Latium.

(...)

Source: High Institute of Health, https://www.epicentro.iss.it/westnile/bollettino/Bollettino_WND_2025_10.pdf

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#Italy, Integrated #Surveillance for #WNV & #USUV - Weekly Bulletin No. 9, 11 September '25 (summary): 80 new cases

{Summary}

-- During current epidemiological week (4 to 10 September), eighty new confirmed human cases of West Nile Virus infection have been reported in Italy.

-- Since the beginning of the epidemic season, there have been a total of 582 confirmed cases (they were 502 last week), of these: 

- 260 were West Nile Neuroinvasive Disease (WNND): 14 in Piedmont, 24 Lombardy, 22 Veneto, 1 Friuli-Venezia Giulia, 1 Liguria, 20 Emilia-Romagna, 3 Tuscany, 77 Latium, 2 Molise, 74 Campania, 1 Apulia, 2 Basilicata, 5 Calabria, 1 Sicily, 13 Sardinia, 

- 48 asymptomatic cases among blood donors, 

- 262 cases of West Nile Fever (1 imported from Kenya), 

- 4 asymptomatic cases, 

- 8 unspecified cases. 

-- A total of 39 fatal cases have been reported so far this season: 5 in Piedmont, 2 Lombardy, 1 Emilia-Romagna, 15 Latium, 14 Campania, 2 Calabria. 

- The Case-Fatality Rate among WNND cases is thus far at 15% (during 2018 season it was 20%, in 2024 14%). 

-- During current surveillance week there were 7 new confirmed Usutu Virus infection cases: 2 in Piedmont, 2 Lombardy, 1 Veneto, 2 Latium.

(...)

Source: High Institute of Health, https://www.epicentro.iss.it/westnile/bollettino/Bollettino_WND_2025_09.pdf

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Shared viral burdens: Evidence of active #Usutu virus circulation and multi- #arbovirus exposure in migrant and resident #birds at wintering locations in #Nigeria

 

Abstract

Background: 

West Nile (WNV), Usutu (USUV), and Sindbis (SINV) virus were initially detected in the African region, and subsequently across temperate regions where they were absent. Wild birds are primary reservoirs for these arboviruses and are considered major contributors to their global spread through seasonal migration. To understand the transmission dynamics of arboviruses in wild birds and the potential of migratory birds to spread the viruses at an intercontinental scale, we investigated arboviral infections and exposures in African resident and Palearctic migratory birds at wintering locations in Nigeria. 

Methodology/Principal Findings: 

Oropharyngeal- and cloacal swabs, feathers and blood were collected from resident and migratory birds at two wintering locations (Amurum and Ngel-Nyaki Forest Reserves). Swabs and feathers were tested using RT-PCR for WNV, USUV and SINV, and blood with ELISA and FRNT90 or PRNT80 for antibodies. 573 birds were sampled between 2021 to 2024 across months coinciding with arrival and departure of migratory birds. USUV RNA was detected in 2.6% of feathers including a positive Icterine warbler and a garden warbler sampled prior to spring migration. None of the swabs was positive for viral RNA but neutralizing antibodies to WNV and USUV were detected in 4.5% of birds. SINV antibodies were also found in 34.1% of birds sampled across the wintering locations. 

Conclusions/Significance: 

Our findings showed that migratory birds can become infected with USUV, and potentially with WNV and SINV during their overwintering periods in Africa and highlighted a wider arbovirus risk in Nigeria. In addition, detections of viral RNA in feathers, but not swabs, suggest feathers may be a suitable matrix for surveillance in the absence of a reliable cold chain. The overall detections in wild birds at these locations highlight the need for further surveillance to define the epidemiology and public health risks of these arboviruses in the region.

Competing Interest Statement

The authors have declared no competing interest.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.09.08.674803v1

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#Italy, Integrated #WNV & #USUV #Surveillance - Weekly #Bulletin No. 7 - 28 August 2025 (summary)

 

{Summary}

-- During surveillance week from 21 to 27 August, 79 new confirmed human cases of West Nile Virus infection have been reported. 

-- Since the beginning of the epidemic season, the total number of confirmed cases have risen to 430 (they were 351 in the last bulletin); of these:

- 193 were West Nile Neuroinvasive Disease cases: 8 in Piedmont, 12 Lombardy, 14 Veneto, 1 Friuli-Venezia Giulia, 1 Liguria, 13 Emilia-Romagna, 62 Latium, 2 Molise, 64 Campania, 2 Basilicata, 5 Calabria, 1 Sicily, 8 Sardinia), 

- 38 were asymptomatic cases among blood donors, 

- 193 were West Nile Fever cases, 

- 3 asymptomatic and 

- 3 unspecified cases. 

-- Among the confirmed cases, there were 27 fatalities: 1 Piedmont, 1 Lombardy, 1 Emilia-Romagna, 11 Latium, 11 Campania, 2 Calabria). 

- The Case-Fatality Rate in WNND cases is so far at 13.9% (during 2018 it was 20%, in 2024 14%). 

-- One confirmed human case of Usutu virus infection has been confirmed in Latium's province of Latina. 

(...)

Source: High Institute of Health, https://www.epicentro.iss.it/westnile/bollettino/Bollettino_WND_2025_07.pdf

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#Italy, #WNV and #Usutu Virus Weekly #Surveillance #Bulletin No. 4, July 7 '25: 84 new confirmed cases (ISS)

{Summary}

-- Since the last update (July 31), eighty-four new confirmed cases of human infection with West Nile Virus have been reported. 

-- Since the start of epidemic season, there were 173 confirmed WNV cases, of which: 

- 72 were West Nile Neuroinvasive Disease (WNND): (2 in Piedmont, 2 Lombardy, 4 Veneto, 1 Friuli-Venezia Giulia, 2 Emilia-Romagna, 37 Latium, 21 Campania, 1 Basilicata, 1 Sardegna), 

- 14 were asymptomatic cases in blood donors, 

- 85 were West Nile Fever cases, 

- 1 was an asymptomatic case 

-- Among the confirmed cases, there were eleven fatalities: 1 in Piedmont, 4 Latium, 6 . 

- The case-fatality rate among WNND cases is at 15% (during 2018 season it was 20%, whereas in 2024 it was 14%). 

-- No new confirmed cases of Usutu Virus human infection have been reported during current surveillance week.

(...)

Source: High Institute of Health, https://www.epicentro.iss.it/westnile/bollettino/Bollettino_WND_2025_04.pdf

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#Italy, Integrated #WNV & #USUV #Surveillance - Bulletin no. 3, July 31 2025 (IZS Teramo): 57 new human cases reported

{Excerpts}

During the epidemiological week comprised between 24 and 30 July 2025, there were fifty-seven new confirmed cases of human infection with West Nile Virus.

-- Since the start of the epidemic season, eighty-nine cases have been reported (there were thirty-two cases in the last week report), of which:

-- forty were WNND (West Nile Neuroinvasive Disease):

- 2 cases in Piedmont, 1 Lombardy, 3 Veneto, 1 Emilia-Romagna, twenty-three Latium, ten Campania);

-- two cases of asymptomatic infection were detected among blood donors (one in Veneto and one in Campania);

-- forty-six cases of West Nile Fever have been confirmed: 

- one in Lombardy, five in Veneto, thirty-five in Latium, four in Campania, one in Sardinia;

-- one asymptomatic case is from Campania;

-- Among confirmed cases, eight fatalities have been recorded: one in Piedmont, two in Latium and five in Campania. The case-fatality rate among WNND so far is at 20% (during epidemic seasons 2018 it was 20% and in 2024, 14%). 

-- The first case of the 2025 season was reported in Piedmont (a sporadic case in Novara Province). The second case was notified on July 3 in Modena Town. 

-- In the current epidemiological week, no confirmed human cases of infection with Usutu virus have been reported.

(...)

Source: National Veterinary Institute of Teramo, https://westnile.izs.it/j6_wnd/home

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#Italy, West Nile Virus (#WNV) and #Usutu Virus Situation #Report, July 24 '25

{Summary}

-- During the Week 17-23 July 2025, Italy reported twenty-seven new cases of human infection with West Nile Virus.

-- Since the beginning of the epidemic season, thirty-two confirmed human WNV infection cases have been reportede (there were five cases in the last update), of these:

- twenty-three were West Nile Neuroinvasive Disease (WNND): 2 in Piedmont, 2 in Veneto, 1 Emilia-Romagna, 15 Latium, 3 Campania),

- one asymptomatic case was detected in a blood donor (Veneto),

- six cases of West Nile Fever have been reported (2 in Veneto, 4 Latium), and two asymptomatic cases (Latium),

- among the cases, there were two fatalities (1 in Piedmont, 1 in Latium).

-- The first confirmed case of the season was detected in Piedmont Region on March 20 2025 (sporadic case), then in Novara Province (July 3rd).

-- No confirmed cases of Usutu Virus infection have been detected so far.

(...)

Source: Istituto Zooprofilattico Sperimentale di Teramo, https://westnile.izs.it/j6_wnd/home

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Re-Emergence of #Usutu Virus and Spreading of #WestNile Virus #Neuroinvasive Infections During the 2024 Transmission Season in #Croatia

Abstract

Neuroinvasive arboviruses such as tick-borne encephalitis virus (TBEV), West Nile virus (WNV), Usutu virus (USUV), and Toscana virus (TOSV) have (re-)emerged with increasing incidence and geographic range. We analyzed the epidemiology of arboviral infections in Croatia during the 2024 transmission season. A total of 154 patients with neuroinvasive diseases (NID), 1596 horses, 69 dead birds, and 7726 mosquitoes were tested. Viral RNA was detected using RT-qPCR. IgM/IgG-specific antibodies were detected using commercial ELISA or IFA, with confirmation of cross-reactive samples by virus neutralization test. RT-qPCR-positive samples were Sanger sequenced. Arboviral etiology was confirmed in 33/21.42% of patients with NID. WNV was most frequently detected (17/11.03%), followed by TBEV (10/6.49%), USUV (5/3.24%), and TOSV (1/0.64%). WNV infections were reported in regions previously known as endemic, while in one continental county, WNV was recorded for the first time. USUV infections re-emerged after a six-year absence. In addition to human cases, acute WNV infections were recorded in 11/395 (2.78%) of horses and two dead crows. WNV IgG seropositivity was detected in 276/1168 (23.63%) and TBEV IgG seropositivity in 68/428 (15.88%) horses. None of the tested mosquito pools were positive for WNV and USUV RNA. Phylogenetic analysis showed the circulation of WNV lineage 2 and Usutu Europe 2 lineage. Climate conditions in 2024 in Croatia were classified as extremely warm, which could, at least in part, impact the quite intense arboviral season. The spreading of flaviviruses in Croatia highlights the need for continuous surveillance in humans, animals, and vectors (“One Health”).

Source: Viruses, https://www.mdpi.com/1999-4915/17/6/846

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