The document discusses the emergence and spread of chikungunya virus (chikv) facilitated by its mosquito vectors, especially Aedes aegypti and Aedes albopictus, highlighting their differing behaviors and susceptibility to the virus. It outlines challenges in vector control and vaccine development, mentioning innovative strategies like Wolbachia and genetically modified mosquitoes to combat transmission. Despite promising vaccines, financial and regulatory hurdles still pose significant obstacles to their approval and use.

1. Scott C. Weaver
Institute for Human Infections and Immunity
and Department of Microbiology and
Immunology,
University of Texas Medical Branch,
Galveston
Chikungunya-Vector Relationships
and Prospects for Control in
Americas and Beyond

2. Aedes
spp.
Ae.
aegyp+
aegyp+
Ae.
albopictus
Sub-Saharan Africa
TSETSARKIN, K. A., CHEN, R., SHERMAN, M. B. & WEAVER, S. C.
2011. Curr Opin Virol, 1, 310-317.
No known
barriers to initial
host range
changes

3. Kraemer, M.U., et al., 2015. The global distribution of the arbovirus vectors Aedes aegypti and Ae. albopictus. Elife 4.
Figure 2. Global map of the predicted distribution of Ae. albopictus. The map depicts the probability of occurrence (from 0 blue to 1 red) at a spatial
resolution of 5 km × 5 km.
DOI: 10.7554/eLife.08347.009
Research article Ecology | Epidemiology and global health
A. albopictus
Originated in Asia, spread to
the Americas, Africa and
Europe beginning in 1985
A. aegypti
Figure 1. Global map of the predicted distribution of Ae. aegypti. The map depicts the probability of occurrence (from 0 blue to 1 red) at a spatial
resolution of 5 km × 5 km.
DOI: 10.7554/eLife.08347.004
The following figure supplements are available for figure 1:
Research article Ecology | Epidemiology and global health
Originated in sub-Saharan
Africa, spread throughout
the tropics centuries ago
Urban Chikungunya Virus Vectors

4. CHIKV Endemic/Epidemic Vectors
Aedes aegypti aegypti
• Tropical and subtropical
• Feeds almost exclusively on humans
• Takes multiple bloodmeals within a
gonotrophic cycle
• Exploits artificial water containers near
houses as larval habitats
• Adult females found mostly inside houses
• Feeds during the daytime
• Moderately susceptible to CHIKV
Aedes albopictus
• Tropics and temperate regions
• Feeds opportunistically
• Usually takes a single bloodmeal within a
gonotrophic cycle
• Uses artificial and natural larval habitats
• Varied levels of anthrophily and endophily
• Feeds during the daytime
• Moderately to highly susceptible to CHIKV
behavior susceptibility

5. CHIKV
Evolution

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lipid bilayers
glycoproteins
E1 & E2
capsid
RNA
nsP1 nsP2 nsP3 nsP4 C E2 E1 Poly[A]-35 cap
26S
(-) strand RNA
synthesis,
RNA capping
Helicase,
proteinase
RNA
synthesis
RNA-dependent
RNA
polymerase
Envelope
glycoproteins
6K
E3
Capsid
Alphavirus Genome and Structure
Zhang, R., et al., 2011. EMBO J 30, 3854-3863.

7. Indian Ocean
epidemics
2005-2011
Asia
2005-2009
Convergent
Evolution of
E1-A226V
Substitution
E1-A226V
Tsetsarkin, K. A., Chen, R., Sherman, M., and Weaver, S. C. (2011).
Curr Opin Virol 1, 310-317 .
Enzootic strains
East, Central,
South Africa
Asian epidemics
1958-2006
Enzootic strains
West Africa

8. 226V 226A
Effect of E1-A226V Mutation on Aedes
albopictus Infectivity
OID50 expressed as Log10TCID50/ml
Schuffenecker I., et al. PLoS Med. 2006;3(7):e263.
Vazeille, M., et al., 2007. PLoS ONE 2, e1168.
Tsetsarkin, K.A., et al., 2007. PLoS Pathog 3, e201.

9. A. albopictus (E1-226V)
Human Infection Profile for CHIKV
Titer(Log10infectiousunits/mlserum)
Days after infection
1 2 3 4 5 6 7 8 9 10
Viremia
IgM
IgG
2
4
6
8
10
Transmission window
Antibodytiter
A. aegypti, A. albopictus (E1-226A)

10. A. albopictus-adaptive
mutations

11. p=0.005
4.86
41.5
4.75
43.5
E2 E1 substitutions
enhance initial
CHIKV infection of A.
albopictus midgut
cells
The E2-L201Q fitness
increase is ca. 10-fold weaker
than E1-A226V and was
selected by A. albopictus only
after ca. 4 years of circulation
in India
Neither E1-A226V nor E2-
L201Q affects infection of A.
aegypti
Tsetsarkin, K.A., Weaver, S.C., 2011. PLoS Pathog 7, e1002412

12. E3; E2; E1 proteins
Natural, second-step adaptive
substitutions of glutamine in
acid-sensitive 210-252 E2 region
A. albopictus-adaptive
mutations in the acid
sensitive region of E2
Hypothesis: Gln or Glu
substitutions in the E2 acid-
sensitive region enhance E1-226V
by regulating low pH-induced E2-
E1 heterodimer disassociation for
efficient CHIKV endosomal entry in
A. albopictus midgut cells.
Support: E2. substitutions are not
in the receptor-binding domain,
and artificial Gln substitutions in
the acid sensitive region also
enhance A. albopictus infectivity. Tsetsarkin KA, et al. Nat Commun. 2014;5:4084. Epub 2014/06/17.

13. Indian Ocean
epidemics
2005-2011
Asia
2005-2009
Convergent
Evolution of
E1-A226V
Substitution
E1-226V
Tsetsarkin, K. A., Chen, R., Sherman, M., and Weaver, S. C. (2011).
Curr Opin Virol 1, 310-317 .
Enzootic strains
East, Central,
South Africa
Asian epidemics
1958-2006
Enzootic strains
West Africa
X

14. Conundrum: Why has A226V mutation not been selected in
Southeast Asia despite endemic circulation in native A. albopictus
territory for ≥57 years?
Explanation: E1-226V does not confer a fitness advantage in
Asian CHIKV strains due to epistatic interactions with E1-98T. This
amino acid, only found in Asian genotype strains, prevents
probably resulted from a founder effect when this genotype was
introduced from eastern Africa in the late 19th or early 20th Century.
Prediction: Most CHIKV strains now circulating in the Americas,
which belong to the Asian genotype, will be more efficiently
transmitted by A. aegypti

15. Prospects for the Control of
Chikungunya Spread
1. Reduction of contact between people and
mosquito vectors
2. Reduction of human amplification using
antivirals
3. Control of transmission by reducing
populations of mosquito vectors
4. Prevention of human infection using vaccines

16. Failure of Traditional Mosquito
Control to Control Dengue
• Adult female A. aegypti remain inside houses, limiting
insecticide penetration from traditional applications
• Larval A. aegypti are found in low density in artificial
containers around homes, requiring entry into individual
properties for inspection/control
• A. aegypti in many parts of the world are developing
resistance to insecticides

17. • Tetracycline repressible activator variant (tTAV): acts as a switch to control the
activity of essential mosquito genes
• tTAV works only in insect cells; the non toxic protein ties up the cell’s machinery
so it’s other genes aren’t expressed and the insect dies in the larval stages
• Tetracycline binds to tTAV and disables it, allowing it to be added to laboratory
larval water so that mosquitoes survive to the adult stage
• Because the tTAV gene is dominant, offspring of matings between released
transgenic and wild mosquitoes die in the wild without tetracycline in their larval
habitats
Novel Approach for Vector Control: Release
of Insects with Dominant Lethality (RIDL)

18. • Safety advantage: transgene is “suicidal”
• Potential limitations: Sustained release of mosquitos is required,
may be too costly for resource-limited regions endemic to CHIKV
Implementation of RIDL:
release of transgenic
male mosquitoes
Field trials: Cayman
Islands, Malaysia,
Panama and Brazil

19. Wolbachia: Bacterial symbionts of many insects that
can spread through populations through cytoplasmic
incompatibility
Female
Male
• When adapted to and introduced into Aedes aegypti, Wolbachia
reduce their lifespan
• Wolbachia also reduce CHIKV (and dengue virus) replication and
transmission

20. Field Trials: Australia (completed),
Indonesia, Viet Nam, Brazil, Colombia
Potential limitations: Limited dispersal of A. aegypti will necessitate
widespread release of female mosquitoes. Can CHIKV (and
dengue virus) evolve resistance to the Wolbachia suppression?

21. CHIK Vaccine Development
The good news:
• Single CHIKV serotype,
no evidence of reinfection
or immune enhancement
• Well established
correlates of protection for
alphaviruses (neutralizing
antibodies)
• Ease of genetic
manipulation for rational
attenuation
• Good nonhuman primate
models for human disease
The bad news:
• Immunocompetent
rodents are poor models
for human disease
• Unpredictable market
after epidemics subside
and CHIKV is rarely
diagnosed
• Unpredictable incidence
of disease for clinical
efficacy trials
• FDA animal rule has not
yet produced a licensed
vaccine

22. Chikungunya Vaccine Development
Bharat Biotech;
VLP vaccine
Takeda and UTMB:
Recombinant live
attenuated CHIK/
IRES
ArboVax;
Recombinant LAIV
Inovio; DNA
vaccine
Themis;
Measles-based
Recombinant
Indian Immunologicals;
Walter Reed strain
US Army, 181/clone25
live attenuated vaccine
based on 2 point
attenuating mutations
Indian Immunologicals;
Inactivated strain 181/
clone 25
Preclinical Phase I Phase II Ph
NIAID;
VLP vaccine
manufactured in
CHO cells
*Merck
option?
Yale, Profectus,
UTMB: VSV-vectored
live-attenuated

23. Summary
• CHIKV has emerged repeatedly, probably for centuries, from its enzootic cycle in
Africa into an urban human-mosquito cycle in Asia, Europe and the Americas.
• The 2005-2015 epidemic has been extensive, in part due to the sequential,
convergent and step-wise adaptation of 5 natural A. albopictus-adaptive envelope
glycoprotein gene mutations, with little or no effect on infection of A. aegypti or
murine models of human infection.
• An epistatic interaction between E1 residues 98 and 226 has prevented the
adaptation of CHIKV for A. albopictus transmission in the Asian lineage, despite
the E1-98 residues having no detectable phenotype. This epistasis should limit
the ability of CHIKV strains in the Americas to adapt for A. albopictus
transmission. An ECSA strain introduced into Brazil in 2014 from Angola also has
an epistatic constraint that may prevent optimal adaptation to this new CHIKV
vector.
• Traditional methods of vector control are unlikely to prevent the spread of CHIKV.
However, new approaches to vector reduction and interference with vector
transmission are more promising
• Several promising vaccines for CHIKV have been developed but financial and
regulatory hurdles represent major obstacles to their licensure

24. Acknowledgements
Funding: NIH-NIAID R01-AI069145, R01-AI071192, R01-AI48807
Konstantin Tsetsarkin
Rubing Chen
Ruimei Yun
Indiana University
Tuli Mukhopadhyay
Institut Pasteur
Amadou Sall
Mawlouth Diallo
Johns Hopkins University
Derek Cummings
Ben Althouse
NM State University
Kathy Hanley