Monitoring Venezuelan Equine Encephalitis In Endemic Regions

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Introduction

Venezuelan equine encephalitis (VEE) is a significant arboviral disease affecting both human and equine populations in endemic regions of the Americas.1 The virus responsible for VEE is a member of the Alphavirus genus, belonging to the Togaviridae family, primarily transmitted through infected mosquitoes, notably of the genus Culex.2 

The monitoring and surveillance of VEE in endemic regions is crucial for early detection, understanding transmission dynamics, and implementing timely control measures. This article delves into the methods, challenges, and importance of monitoring VEE in these regions.

Understanding VEE

Background 

The VEE virus is classified into complex antigenic varieties (subtypes) with distinct ecologies and organisms involved in causing the disease.3 The virus circulates involving rodents and mosquitoes, with occasional spillover into equine (horses etc) and human populations.2 Infected equines often develop clinical symptoms such as fever, lethargy, and neurological symptoms, while humans may experience flu-like symptoms progressing to severe encephalitis.

Transmission pathways

Transmission of the VEE virus primarily occurs through mosquitoes.2 These mosquitoes acquire the virus by feeding on infected animal hosts and subsequently transmitting it to individuals during their blood meals. The VEE virus can also be transmitted within mosquito populations, contributing to its persistence during inter-epidemic periods.7

Symptoms and impact on human and horse populations 

Clinical manifestations of VEE infection vary, ranging from mild fever to severe encephalitis with high mortality rates.2 Equines are particularly vulnerable, experiencing acute onset of illness characterised by: 

  • Fever 
  • Anorexia 
  • Neurological signs such as ataxia and seizures 

In humans, VEE infection can lead to neurological complications, including:2 

  • Seizures, 
  • Coma, and 
  • Long-term neurological deficits 

The disease can have a significant negative on the economy also, due to losses in equine productivity and healthcare costs associated with human cases.

Surveillance methods

Sentinel animal surveillance 

Sentinel animal surveillance plays a crucial role in detecting VEE virus activity in endemic regions.4,5 Equines, particularly horses, serve as sentinel animals due to their susceptibility to infection and the manifestation of clinical symptoms. Blood samples collected from sentinel animals are tested for VEE virus-specific antibodies using serological assays, providing evidence of virus circulation in the area.

Mosquito surveillance 

Monitoring mosquito populations provides insights into the spatial and temporal distribution of potential VEE virus vectors (both carriers and spreaders of the disease).5 Various trapping methods capture adult mosquitoes for species identification and virus detection. These include:

  • Light traps 
  • Gravid traps
  • Resting box traps

Mosquito pools are also tested for VEE virus using molecular methods such as reverse transcription-polymerase chain reaction (RT-PCR), enabling early detection of viral activity.

Syndromic surveillance in humans

Syndromic surveillance involves monitoring clinical syndromes associated with VEE infection in humans.4,5 Healthcare facilities report cases presenting with compatible symptoms to public health authorities, including: 

  • Fever
  • Headache
  • Neurological abnormalities 

Timely data collection and analysis enable the swift application of targeted control measures and public health interventions.

Geographic information systems (GIS) mapping

Utilising GIS for monitoring VEE 

GIS technology provides a powerful tool for visualising and analysing spatial data related to VEE transmission dynamics.4 Geographic mapping of VEE cases, mosquito habitats, and environmental factors enables the identification of high-risk areas, which helps with the application of targeted surveillance and control strategies.

Mapping of confirmed cases and mosquito habitats 

The combination of epidemiological data with environmental variables such as temperature, precipitation, and land cover, makes it easier to identify environmental drivers influencing VEE transmission.4 GIS mapping of confirmed VEE cases and mosquito habitats enables the identification of spatial clusters and the prioritisation of surveillance efforts in high-risk areas.

Integration of environmental factors for risk assessment 

Incorporating environmental factors into risk assessment models enhances our understanding of the ecological drivers of VEE transmission.4 Predictive modelling based on GIS data allows for the identification of areas vulnerable to VEE outbreaks, which helps guide proactive surveillance and control measures.

Laboratory diagnostics

Techniques 

Accurate laboratory diagnostics are essential for confirming VEE virus infection in sentinel animals, mosquitoes, and humans.3 Serological assays, including enzyme-linked immunosorbent assays (ELISA) and plaque reduction neutralization tests (PRNT), detect VEE virus-specific antibodies in serum samples. Molecular methods such as RT-PCR enable the direct detection of viral RNA in biological specimens, providing rapid and sensitive diagnostic results.7

Laboratory protocols and quality assurance measures

Standardised laboratory protocols and quality assurance measures ensure the reliability and accuracy of diagnostic test results.4,5 Quality control procedures, proficiency testing, and external quality assessment programs help maintain the integrity of laboratory testing and data interpretation.

Collaboration with reference laboratories 

Collaboration with reference laboratories strengthens diagnostic capabilities and facilitates the exchange of expertise and resources.4,5 Reference laboratories play a vital role in confirming VEE virus isolates, characterising viral strains, and researching to improve diagnostic methods and surveillance techniques.

Data analysis and interpretation

Compilation and analysis 

Systematic compilation and analysis of surveillance data provide valuable insights into VEE transmission dynamics and trends.3 Epidemiological analyses, including temporal and spatial mapping of cases, allow for the identification of patterns and risk factors associated with VEE outbreaks.

Identification of trends and hotspots

Data analysis makes the identification of emerging trends and hotspots of VEE virus activity easier.3 Surveillance data are analysed along with environmental variables to identify ecological drivers influencing VEE transmission and spread.

Assessment of contributing risk factors  

Assessing risk factors contributing to VEE transmission enhances our understanding of the epidemiology of the disease.3,4,5 Factors such as climate variability, land use changes, and mosquito vector dynamics influence the spatial and temporal distribution of VEE virus activity, informing proactive risk mitigation strategies.6

Response and control measures

Early warning systems based on surveillance data 

Early warning systems based on surveillance data make the timely detection of VEE outbreaks and implementation of control measures easier.4,5 Thresholds for case reporting trigger rapid response activities, including: 

  • Mosquito control interventions 
  • Vaccination campaigns
  • Public health messaging

Vector control strategies

Vector control strategies aimed at reducing mosquito populations are essential to VEE prevention and control efforts.4,5 Combined vector management approaches target mosquito breeding sites and minimise vector-human contact. These include: 

  • Larval source reduction 
  • Insecticide spraying
  • Community-based mosquito control programs

Public health interventions

Public health interventions focus on preventing human VEE infections and mitigating the impact of outbreaks on affected communities.4,5 Health education campaigns promote personal protective measures such as: 

  • Mosquito repellent use 
  • Bed netting
  • Environmental sanitation practices 

Vaccination of at-risk populations, including equine and laboratory personnel, provides additional protection against VEE virus exposure and spread.

Challenges and future directions

Limitations of current monitoring approaches

Despite advances in surveillance and diagnostic techniques, challenges remain in effectively monitoring VEE within endemic regions.1 Limited resources, logistical constraints, and gaps in surveillance coverage pose obstacles to early detection and response efforts.5

Research needs

Addressing research gaps is essential for enhancing VEE surveillance and control strategies.1 Research priorities include: 

  • The development of novel diagnostic tools
  • Predictive modelling of VEE transmission dynamics
  • Evaluation of integrated vector management approaches

Importance of international collaboration

Collaboration among national and international stakeholders is critical for combating VEE and mitigating its global impact.1 Sharing of data, resources, and expertise makes it much easier to coordinate surveillance, outbreak response, and research initiatives aimed at reducing the burden of VEE in endemic regions.

Summary

  • Monitoring VEE in endemic regions is essential for early detection, prevention, and control of this significant arboviral disease. 
  • Surveillance approaches combining sentinel animal, mosquito, and syndromic surveillance, along with GIS mapping and laboratory diagnostics, provide valuable tools for monitoring VEE transmission dynamics. 
  • Addressing challenges and advancing research priorities will enhance our ability to reduce the impact of VEE on human and animal health, highlighting the importance of sustained surveillance efforts in endemic regions.

References

  1. Weaver SC. Host range, amplification and arboviral disease emergence. Archives of virology Supplementum. 2005 [cited 11 March 2024]; 2005(19):33-44. Available from: https://link.springer.com/chapter/10.1007/3-211-29981-5_4 
  2. Weaver SC, Barrett AD. Transmission cycles, host range, evolution and emergence of arboviral disease. Nature Reviews Microbiology. 2004 [cited 11 March 2024]; 2(10):789–801. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7097645/ 
  3. Powers AM, Oberste MS, Brault AC, Rico-Hesse R. Repeated emergence of epidemic/epizootic Venezuelan equine encephalitis from a single genotype of enzootic subtype ID virus. Journal of virology. 1997 [cited 11 March 2024]; 71(9):6697–705. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC191949/pdf/716697.pdf 
  4. Estrada-Franco JG, Navarro-Lopez R, Freier JE. Venezuelan equine encephalitis virus activity in the Gulf Coast region of Mexico, 2003-2010. PLoS neglected tropical diseases. 2001 [cited 11 March 2024]; 6(11):e1875.. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3486887/ 
  5. Carrera JP, Forrester N, Wang E, Vittor AY, Haddow AD, López-Vergès S, et al. Eastern equine encephalitis in Latin America. New England Journal of Medicine. 2013 [cited 11 March 2024]; 369(8):732–44. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3839813/ 
  6. Brown HE, Childs JE, Diuk-Wasser MA, Fish D. Ecological factors associated with West Nile virus transmission, northeastern United States. Emerging infectious diseases. 2008 [cited 11 March 2024]; 14(10). Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2609885/ 
  7. Greene IP, Wang E, Deardorff ER, Milleron R, Domingo E, Weaver SC. Effect of alternating passage on adaptation of sindbis virus to vertebrate and invertebrate cells. Journal of virology. 2005 [cited 11 MArch 2024]; 79(22):14253–60. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1280187/

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Mezad Firdosh Zaiwala

Master's degree, Public Health, University of Bristol

With a background in veterinary medicine and a Master's in Public Health, Mezad Zaiwala embodies a unique blend of expertise in animal care and public health advocacy. Their journey began in veterinary clinics, where they cultivated their clinical skills and nurtured a deep connection with animals and their caregivers.

Driven by a desire to address broader health challenges, Mezad Zaiwala pursued a Master's degree in Public Health, delving into topics such as epidemiology, health policy, and environmental health. This interdisciplinary education equipped them with a comprehensive understanding of the intricate relationship between animal health, human health, and environmental factors.

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