# Vector-Borne Disease Prevention in a Changing Climate

## Overview

Vector-borne diseases account for >17% of all infectious diseases globally and cause >700,000 deaths/year. In the U.S., tick-borne diseases (especially Lyme disease) are the most common, with mosquito-borne diseases of increasing concern. Climate change is expanding vector geographic range, lengthening transmission seasons, and altering disease ecology. Integrated vector management (IVM) combines biological, chemical, environmental, and personal protection strategies. Preventive medicine physicians advise on prevention, surveillance, and community-level response to vector-borne threats.

## Major Vector-Borne Diseases in the U.S.

### Tick-Borne Diseases

#### Lyme Disease (Borrelia burgdorferi)

Most common vector-borne disease in the U.S. (~476,000 estimated cases/year) Vector: Ixodes scapularis (black-legged/deer tick) in the East, Ixodes pacificus in the West. Endemic in Northeast, Mid-Atlantic, and Upper Midwest; range expanding northward. Clinical stages: early localized (erythema migrans, 70-80%), early disseminated (multiple EM, carditis, cranial nerve palsy), late disseminated (arthritis, encephalopathy) Diagnosis: clinical + two-tier serologic testing (EIA followed by Western blot or second EIA) Treatment: doxycycline (first-line for adults and children >8) Prevention: tick avoidance, permethrin-treated clothing, DEET, tick checks, prompt tick removal (<36 hours reduces transmission risk) Post-exposure prophylaxis: single dose doxycycline 200 mg if tick attached >36 hours in endemic area.

#### Other Tick-Borne Diseases

**Anaplasmosis** (Anaplasma phagocytophilum): fever, headache, leukopenia, thrombocytopenia; doxycycline. **Babesiosis** (Babesia microti): hemolytic anemia, fever; atovaquone + azithromycin; can be severe in asplenic/immunocompromised. **Ehrlichiosis** (Ehrlichia chaffeensis): Lone Star tick; similar to anaplasmosis; doxycycline. **Rocky Mountain Spotted Fever** (Rickettsia rickettsii): potentially fatal; rash (often late), fever, headache; doxycycline -- treat empirically, do not wait for confirmatory testing. **Powassan virus**: rare but severe encephalitis; no specific treatment; transmitted within 15 minutes of tick attachment. **Alpha-gal syndrome**: red meat allergy following Lone Star tick bite; IgE-mediated delayed anaphylaxis.

### Mosquito-Borne Diseases

#### West Nile Virus (WNV)

Most common domestic mosquito-borne disease in the U.S. Vector: Culex mosquitoes; bird reservoir with humans as dead-end hosts. ~80% asymptomatic; ~20% febrile illness; <1% neuroinvasive disease (meningitis, encephalitis, acute flaccid paralysis) No vaccine or specific treatment for humans. Prevention: mosquito control, personal protection (DEET, picaridin), eliminating standing water.

#### Dengue

Aedes aegypti and Aedes albopictus mosquitoes. ~400 million infections globally/year; locally acquired cases increasing in U.S. (Florida, Texas, Hawaii) Four serotypes; secondary infection with different serotype carries risk of severe dengue/dengue hemorrhagic fever. Dengvaxia vaccine: FDA-approved for seropositive individuals ages 9-16 in endemic areas (risk of severe disease if given to seronegative)

#### Zika Virus

Aedes mosquitoes; also sexually transmitted. Congenital Zika syndrome: microcephaly, brain abnormalities, ocular defects, arthrogryposis. Guillain-Barre syndrome in adults. No vaccine available; prevention through mosquito control and travel advisories for pregnant women. Large 2015-2016 epidemic; currently low transmission but endemic in tropical regions.

#### Other Mosquito-Borne Threats

**Chikungunya**: severe polyarthralgia; expanding range with Aedes mosquitoes; vaccine (Ixchiq) FDA-approved 2023. **Eastern Equine Encephalitis (EEE)**: rare but high fatality (~30%); no specific treatment. **Malaria**: not endemic in U.S. but ~2,000 imported cases/year; locally acquired cases reported in 2023 (Florida, Texas, Maryland)

| Disease | Pathogen | Vector | Geographic Range (U.S.) | Key Clinical Feature | Treatment |
|---|---|---|---|---|---|
| Lyme disease | Borrelia burgdorferi | Ixodes scapularis/pacificus | Northeast, Mid-Atlantic, Upper Midwest | Erythema migrans (70-80%) | Doxycycline |
| Anaplasmosis | Anaplasma phagocytophilum | Ixodes scapularis | Northeast, Upper Midwest | Leukopenia, thrombocytopenia | Doxycycline |
| Babesiosis | Babesia microti | Ixodes scapularis | Northeast, Upper Midwest | Hemolytic anemia | Atovaquone + azithromycin |
| RMSF | Rickettsia rickettsii | Dermacentor variabilis/andersoni | Southeast, South-central | Rash (often late), potentially fatal | Doxycycline (empiric) |
| West Nile | West Nile virus | Culex mosquitoes | Nationwide | Neuroinvasive disease (<1%) | Supportive only |
| Dengue | Dengue virus (4 serotypes) | Aedes aegypti/albopictus | FL, TX, HI (locally acquired) | Severe dengue on secondary infection | Supportive |
| Zika | Zika virus | Aedes aegypti/albopictus | Previously FL, TX; low currently | Congenital Zika syndrome | Supportive; prevention focus |

## Climate Change and Vector-Borne Disease

### Mechanisms of Change

**Range expansion**: warmer temperatures allow vectors to survive in previously inhospitable latitudes and altitudes. Ixodes ticks expanding northward in U.S. and Canada at ~46 km/year. Aedes mosquitoes establishing in temperate zones previously too cold for sustained populations. **Longer transmission seasons**: earlier spring onset and later fall extend the period of vector activity. **Altered reproduction and development**: warmer temperatures accelerate mosquito development and shorten pathogen incubation period (extrinsic incubation period) **Extreme weather events**: flooding creates mosquito breeding habitat; drought concentrates vectors and hosts around water sources. **Ecological disruption**: changes in host species distribution and abundance affect transmission dynamics.

### Projections

Billions of additional people at risk for dengue, malaria, and other mosquito-borne diseases by 2050-2100. Lyme disease endemic area in North America projected to expand significantly. Novel pathogen-vector combinations may emerge as ranges overlap in new ways.

## Integrated Vector Management (IVM)

### Environmental Management

Source reduction: eliminating standing water, improving drainage, maintaining vegetation. Habitat modification: wetland management, housing improvements (screens, sealed eaves) Community clean-up campaigns targeting mosquito breeding sites (tires, containers, gutters)

### Biological Control

Larvivorous fish (Gambusia) in permanent water bodies. Bacillus thuringiensis israelensis (Bti): biological larvicide, highly specific to mosquitoes. Wolbachia-infected mosquitoes: sterile insect technique; reduces Aedes population and dengue transmission. Genetically modified mosquitoes: gene drive technology (emerging, controversial)

### Chemical Control

Larvicides: applied to water bodies to kill mosquito larvae (Bti, methoprene) Adulticides: space spraying (ULV application) for acute outbreak response. Residual spraying: indoor residual spraying (IRS) with insecticides (primarily for malaria) Acaricides: targeted treatment for tick control in peridomestic environments. Insecticide resistance is a growing concern (monitoring through bioassays) Environmental and ecological concerns with broad-spectrum insecticides.

### Personal Protection

EPA-registered repellents: DEET (20-30%), picaridin (20%), IR3535, oil of lemon eucalyptus (OLE) Permethrin-treated clothing and gear. Long sleeves and pants in endemic areas. Bed nets (insecticide-treated nets, ITNs) for malaria-endemic travel. Tick checks after outdoor activity; prompt removal with fine-tipped forceps. Avoid outdoor activity during peak mosquito hours (dawn and dusk for many species)

## Surveillance Systems

ArboNET: CDC national surveillance system for arboviral diseases. State and local mosquito surveillance: trapping, species identification, virus testing. Tick surveillance: passive (submitted ticks) and active (drag sampling) surveillance. Climate-informed predictive models for vector activity and disease risk. Citizen science: tick identification apps and submission programs.

<image>A map of the United States showing the current and projected expanded range of Ixodes scapularis (black-legged tick) under climate change scenarios. The current Lyme disease endemic area (Northeast, Mid-Atlantic, Upper Midwest) is shown in one color, with projected range expansion by 2050 and 2080 shown in additional colors extending northward and westward. An inset shows the annual reported Lyme disease cases trend from 2000 to 2024. Climate change and vector-borne disease education map.</image>

<image>A diagram showing the integrated vector management (IVM) approach with four quadrants: Environmental Management (source reduction, habitat modification), Biological Control (Bti, Wolbachia, larvivorous fish), Chemical Control (larvicides, adulticides, IRS), and Personal Protection (repellents, permethrin-treated clothing, tick checks, bed nets). At the center, "Surveillance and Monitoring" connects all quadrants. Each quadrant includes specific examples with icons. Vector-borne disease prevention education illustration.</image>

<image>An infographic showing the lifecycle of Ixodes scapularis (deer tick) across four stages: egg, larva, nymph, and adult, with the animal hosts at each stage (mice for larvae, mice/small mammals for nymphs, deer for adults). The diagram shows that nymphs are responsible for most Lyme disease transmission to humans (small size, peak activity in spring/summer, high Borrelia infection rate). Key prevention interventions are mapped to each lifecycle stage. Tick-borne disease prevention education illustration.</image>

## Clinical Pearls

The nymphal stage of Ixodes ticks is responsible for most Lyme disease transmission -- nymphs are tiny (poppy seed-sized), active in spring/summer, and often go undetected. Rocky Mountain Spotted Fever requires empiric doxycycline treatment at clinical suspicion -- waiting for serologic confirmation can be fatal. Doxycycline is safe in children of all ages for short courses (AAP) -- do not withhold for suspected tick-borne disease in children. Climate change is not a future threat to vector-borne disease -- range expansion is happening now, and clinicians in newly endemic areas must recognize diseases they have not historically encountered. For boards: know the vectors for major diseases (Ixodes for Lyme, Aedes for dengue/Zika, Culex for WNV), the approach to Lyme post-exposure prophylaxis, and the components of integrated vector management.

## References

- CDC. Lyme Disease. cdc.gov; 2024.
- Ogden NH, et al. Estimated effects of projected climate change on the basic reproductive number of the Lyme disease vector. Environ Health Perspect. 2014;122(6):631-638.
- Rosenberg R, et al. Vital signs: trends in reported vectorborne disease cases -- United States and territories, 2004-2016. MMWR. 2018;67(17):496-501.
- Eisen RJ, Eisen L. The blacklegged tick, Ixodes scapularis: an increasing public health concern. Trends Parasitol. 2018;34(4):295-309.
- WHO. Global Vector Control Response 2017-2030. WHO; 2017.