Download Apparent Resurgence of Vector‐ borne Disease in the 21st Century

Apparent Resurgence of Vector‐
borne Disease in the 21st Century
David M. Claborn, DrPH
Master of Public Health Program
Master of Public Health Program
Missouri State University
Definitions:
• Reservoir – the animal in which a disease agent (virus, bacteria, etc.) usually resides and develops to a stage and population that can infect a ll
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vector. A reservoir can be an animal (ex. rodents or birds), humans, or even the vector population itself (ex. some ticks can serve as reservoirs). • Vector – (strict definition) an arthropod that picks up a disease agent from a reservoir, supports some type of development or reproduction of the agent in its own body, then transmits the infectious agent to a susceptible host.
• Host‐ an animal which becomes infected as a result of the bite of a vector. A host may also serve as a reservoir, infecting other vectors, but may be a ‘dead end’ host which cannot infect vectors.
Modified Epidemiologic Triad to Describe Vector‐borne Disease
Vector
Agent
Environment
Host
Primary vector‐borne
Primary vector
borne diseases world wide
diseases world wide
•
•
•
•
•
•
•
•
•
•
•
Malaria
Dengue fever
Dengue fever
Chicungunya
Yellow fever
West Nile virus
West Nile virus
Eastern Equine Encephalitis
Japanese encephalitis
Rift Valley Fever
Rift Valley Fever
Filariasis (elephantiasis)
Onchocerciasis (river blindess)
Sand fly fever
y
•
•
•
•
•
•
•
•
•
•
•
Tick‐borne encephalitis
Lyme disease
Lyme disease
Bubonic plague
Typhus
Tick‐borne relapsing fever
Tick‐borne relapsing fever
Babesiosis
Tularemia
Leishmaniasis
Chagas’ disease
African sleeping sickness
Oropouche
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• And many more, especially viruses.
Reasons for emerging and re‐emerging vectorborne
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diseases
• 1. Travel and trade
• Invasive species
• 2. Adaptation of the agent
• 3. Adaptation of the vector
3 Adaptation of the vector
• 4. Insecticide resistance
5. Antibiotic resistance?
• 5. Antibiotic resistance?
• 6. Elimination of vector control programs
• 7. Environmental change
1. Travel and trade
1. Travel and trade
• Rapid travel by air allows traveler to arrive before onset of disease symptoms.
• Immigration
• Trade in items that harbor vectors
Trade in items that harbor vectors
• Introduction of invasive species
The Infamous Yellow Fever mosquito, Aedes
aegypti
CDC estimate of cites at risk of Zika transmission as estimated by the National Center of Atmospheric research (2016): Analysis based on variables of climate, mosquito breeding patterns, poverty and air travel trends.
An invasive species: Ae. albopictus, the Asian Tiger Mosquito. How does it affect extant species
Tiger Mosquito. How does it affect extant species like Ae. aegypti ?
Spread of Aedes
albopictus between 1985‐
between 1985
1996 after its initial introduction.
(Image from Moore & (Image
from Moore &
Mitchell, EID 3(3): 334
MSU survey of mosquitoes in Missouri funded b Mi
by Missouri DHSS (Contract APC16380144)
i DHSS (C
APC16380144)
Area of the mosquito survey done during the summer of 2016. Counties in tan colors are those that were surveyed for adult and larvae. Aedes aegypti in Missouri:
Specimens were found in counties colored red. (note: ti
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None of the counties are colored red)
Aedes albopictus in Missouri. Specimens (adult or immature) were collected in all counties Aedes albopictus distribution as colored red. None were collected in counties detected
detected by adult and larval survey in by sampling
adult andinlarval
survey
in
colored
colored tan. No sampling in counties colored tan No
counties
colored
black.summer of 2016. Species was detected in all counties colored red in the figure. (Christian County was under sampled)
Aedes japonicus: Specimens (adult or larval) were
(adult or larval) were collected in all counties colored blue. No sampling was done in counties colored black
2. Adaptation of the agent
2. Adaptation of the agent
• The case of chikungunya and a single mutation.
• Spread of virus historically limited by distribution of the yellow fever mosquito.
• Due to a single point mutation (E1‐Ala226Val) in the virus, the virus was able to efficiently infect another mosquito species with a broader range. (Ae. ffi i l i f
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(A
albopictus) the Asian tiger mosquito.
• Allowed much greater range and led to expansion out of Africa and across the Indian Ocean The mutation has spread from there to France Italy and by
Indian Ocean. The mutation has spread from there to France, Italy, and by 2013 to North and South America.
3. Adaptation of the vector species
3. Adaptation of the vector species
• Insecticide resistance
• Adaptation to a new environment
• Example of Yellow fever mosquito (Ae. aegypti) adaptation to water quality.
quality
Image from “Dengue/Dengue Hemorrhagic Hemorrhagic
fever: the emergtence of a global Health Problem.” EID 1(2): 55‐57
( )
Adaptation to new environments or “How I l
learned to to live with and love the septic tank.”
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4. More adaptation: Development of resistance: Insecticide or antibiotic
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• 1. Insecticide vs. repellent. (Why DDT has made a comeback with the WHO).
• 2. Antibiotic resistance by the agent.
2 Antibiotic resistance by the agent
…adaptations by the agent and the vector.
…adaptations by the agent and the vector.
• Lowe CF, Romney MG. “Bedbugs as vector for drug resistant t f d
it t
bacteria.” Emerging Infectious Disease, (June) 2011
• Not proven vector status yet but good reason to suspect as the vector of vancomycin‐resistant t
f
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Enterococcus faecium (VRE) and methicillin‐resistant S. aureus (MRSA) (MRSA)
Environmental change
Environmental change
• 1. Urbanization and dengue
• 2. Deforestation and malaria
• 3. Reforestation with increase in deer population and Lyme
• 4. Rapid climate change/global warming?
Elimination of vector control programs
Elimination of vector control programs
• The WHO malaria eradication program and its effects on multiple vectorborne diseases.
• Elimination of the program coincides with return of malaria, dengue, chikungunya.
• Effect on developed world may be minimal for most of the population, but devastating for those affected. • Example: Survey of Missouri Vector Control Preparedness Have you had any training or education in vector surveillance, vector control or vector biology within the last 5 years? (directors of agency)
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? (di t
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)
Has anyone on your staff had any training or education of vector surveillance, control or biology within the last five years?
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ithi th l t fi
?
Who would conduct emergency vector control in your county if it was needed?
Does your county maintain stocks of vector surveillance and control equipment?
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t?
Conclusions:
• The reason for recent emergences and resurgence of vectorborne diseases is multifactorial
is multifactorial. • In the U.S., much of the situation can be explained by reforestation (Lyme disease). Some natural events (spread of WNV). • In Missouri, much of the situation can be explained by the ability to I Mi
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identify new agents (Bourbon; Heartland)
• The effect of invasive species is, at present, unknown. Potential displacement of Ae aegypti by albopictus
displacement of Ae. aegypti
by albopictus could be good or bad for the Zika
could be good or bad for the Zika
situation. • Elimination of vector surveillance and control programs have played major roles in the resurgence of vector‐borne diseases on a worldwide basis
roles in the resurgence of vector‐borne diseases on a worldwide basis. Questions or comments?
Questions or comments?