Surveillance of Vector Borne Diseases

VBD facts and stats

• Vector-borne diseases account for more than 17% of all infectious diseases, causing more than 1 million deaths annually.

• More than 2.5 billion people in over 100 countries are at risk of contracting dengue alone.

• Malaria causes more than 400 000 deaths every year globally, most of them children under 5 years of age.

• Other diseases such as Chagas disease, leishmaniasis and schistosomiasis affect hundreds of millions of people worldwide.

Many vector Borne Diseases are ________.

preventable through informed protective measures.

Risk factors of mosquito-borne disease in the U.S.

• Migrating birds.

• Lack of mosquito control at ports of entry.

• High quantities of vectors in area of concern.

• Lack of public education.

• Lack of funding for surveillance and equipment.

• Lack of funding for insecticide resistance testing.

• Vector competence of mosquitoes, host susceptibility, lack of surveillance-based targeted control, time spent outdoors (mosquito-human contact).

• Increased global travel

• Climate change and natural disasters (e.g., hurricanes)

Invasive mosquitoes

• Introduction, establishment, and spread of invasive mosquito species (globalization of trade/travel) is concerning.

• they compete with native species, transmit disease pathogens, biting nuisance, etc. (e.g. Aedes albopictus)

• Lack of mosquito control infrastructure at ports of entry.

Framework for surveillance and vector Borne diseases (emerging and re-emerging)

• Prevent introduction of invasive species

• Prevent spread of invasive species into new areas

• Prevent vector borne disease outbreaks

• Improve entomological surveillance of mosquitoes

• Improve human disease management, reduce morbidity/mortality 

• Improve public education about mosquito-borne disease (PSAs, school curriculum, etc.)

Preventing introduction of invasive species

• Restrictions on importation of high risk goods and/or use of pesticides

• Changes in packaging, ex: pack bamboo in hydrogel rather than standing water

• quarantine step for packages

• Ex: Imported goods from countries with Japanese beetles need to have palettes irradiated.

• Ex: importation via used tires, Lucky bamboo

Preventing spread of invasive species in new areas

• Entomological surveillance in early phases of colonization

• Pesticides targeting immature and adult mosquitoes

Integrated surveillance should be ______.

analyzed and used to decide on control measures

• ex: vector control when vector populations above a certain level

Entomological surveillance

• trapping mosquitoes and identifying

• larval surveys

Epidemiological surveillance

case-reports

Risk factor surveillance

• indices (House index, Container index, breteau index)

• standing water

Preventing outbreaks

• National preparedness plans in place to respond to early signs of outbreaks when local transmission has been observed.

• Rapid communication between local and regional health authorities essential.

• Sustained federal/state funding for mosquito control programs is needed (currently not the case).

Improving human disease management

• Early and efficient diagnosis crucial to management.

• Misdiagnosis a problem as symptoms of vector borne disease may be complex and vary at different phases of infection.

• Laboratory confirmation is important to exclude other diseases and to ensure proper treatment.

• Molecular and serological techniques.

Political support

• Advocacy should be based on surveillance data, risk analysis, and data on effectiveness of control methods.

• Disease prevention should not be political.

Communication strategies

• Physicians should be alerted to clinical signs and symptoms of vector borne diseases that could be mistaken for other viral or parasitic diseases.

• Health agencies should alert the public where local cases have been reported.

• Programs need to communicate with each other.

Components of Vector Borne Disease Surveillance

1. Disease in humans or domestic animals

2. Vector surveillance for pathogen

3. Wild vertebrate host surveillance

4. Weather patterns related to pathogen transmission

   • Affects vectors and vertebrate hosts

ArboNET

• National surveillance system for arboviral disease in US.

  • CDC - DVBD.

• Set up in 2000 after WNV entered the US (1999).

• In 2003, several non-WNV arboviruses added.

• Cases mapped by CDC and USGS

The arboNET monitors the ______.

epidemiology, incidence, and spread of WNV and other arboviruses.

• State health departments send data to CDC weekly

• Inform public health officials, government leaders, researchers, clinicians, and the public.

• Support control efforts, encourage arboviral disease research.

• Detect spatial patterns of emerging/re-emerging pathogens

Types of pathogen surveillance

• cell cultures

• molecular biology

• seroepidemiology

Seroepidemiology

examination of sera for antibodies

• Determine virus spread, geographical distribution, and virus prevalence

• sentinel chickens

Sentinel chickens

chickens in a vector control programs that serve as an early warning system for mosquito-borne viruses or avian flu

• Regular blood tests to detect antibodies from mosquito Borne disease or avian flu

Cell culture

• presence/absence of live virus

• quantification of virus titer (concentration of viruses in a sample)

Molecular biology

Identify and differentiate virus isolates from individuals and geographic areas

A virus with similar genotype can _______.

show different phenotypes

• ex: Small West Nile virus plaque variant in mammalian cells showed minor nucleotide differences in virus membrane protein and one non-structural protein. 

• ex: Mutation caused phenotypic differences in vector competence in Culex pipiens pipiens (i.e. lower dissemination and transmission rates)

Electron cryomicroscopy

• Rapid freezing (liquid nitrogen)

• Permits visualization of particle.

  • Reconstruct 3-D images from frozen virus particle.

Enzyme Linked Immunosorbent Assay is a ______.

serologic method to detect antibodies or antigen

Quantative polymerase chain reaction detects ______.

virus nucleic acid

• reverse transcription in real-time

How to screen collected mosquitoes for viruses in Vero Cells

1. Mosquitoes collected in the field are sorted according to species.

2. Mosquitoes are then homogenized using a mixer mill.

3. The resulting mosquito homogenate is inoculated into separate Vero cell cultures. 

4. Mosquito homogenates are placed on a shaker for 5 minutes.

5. The inoculated cell cultures are incubated at 37°C to allow for virus replication. 

6. Ultimately, the cultures are examined visually for evidence of viral induced cytopathic effects.

Viable virus

• Is the virus alive and multiplying?

• methods: plaque assay (cells) and cytopathic effects in cell culture

• explanation: virus infects/kills cells in dish

Testing methods for viable virus

• plaque assay

• cytopathic effects in cell culture

Testing methods for Virus antigen

• Immunoflorescent assay (IF A)

• Enzyme Linked Immunoassay (ELISA)

• Hemagglutination Inhibition (HI)

Testing methods for Nucleic acid detection

• PCR

• Reverse Transcription Polymerase Chain Reaction (RT-PCR)

• quantitative reverse transcription polymerase chain reaction (qRT-PCR)

Testing methods for serology

• general antibody detection

• plaque reduction neutralization test

• Immunofluorescent assay

• Enzyme linked Immunoassay

• hemagglutination assay

Virus antigen

• looking for virus pieces, like proteins

• methods: Immunofluorescent assay (IF A), Enzyme Linked Immunoassay (ELISA), and Hemagglutination Inhibition (HI)

• detects viral proteins with glowing tags, color change, or blood cells clumping

Nucleic acid detection

• looking for the virus’s genetic code

• methods: PCR, Reverse Transcription Polymerase Chain Reaction, and quantitative reverse transcription polymerase chain reaction

• copies DNA/RNA so virus can be seen or measured

Serology

• looking for body’s antibodies

• methods: general antibody detection, plaque reduction neutralization test, Immunofluorescent assay, Enzyme linked Immunoassay, and hemagglutination assay

• checks if body made antibodies or if the antibodies block the virus