Roadmap for Vector Transmission Control (VTC)

What are we trying to achieve and why? What is the problem we are trying to solve?

To decrease pathogen transmission by reducing the vector’s down or up-modulation of the host immune reaction

What are the scientific and technological challenges (knowledge gaps needing to be addressed)?

• Elucidate mechanisms of host immunomodulation by vectors to determine how the vector is reducing protective host immune responses
• Identify immunosuppressive components in vector saliva and thus their role in transmission of pathogens
• Further research is needed to develop new vaccines or treatments that target the specific mechanisms by which mosquito saliva enhances disease transmission. (Is this by immunosuppressants in the saliva or is it other factors such as anti-coagulants?)
• Identify the specific components in mosquito saliva that attract dendritic cells and how this attraction contributes to immune responses
• Determine what are the interactions between host compounds and vector saliva and how this affects immunosuppression
• Determine the difference in feeding regularity and other behaviours of infected vs. noninfected vectors. E.g., infected sandflies regurgitate gut contents and spread infection
• Determine which vector factors are facilitating pathogen transmission and how they relate to those causing immunosuppression
• Increase our understanding of the effects of mosquito feeding on immune responses in flavivirus-resistant mice: while mosquito feeding has been shown to modulate cytokines in flavivirus-susceptible mice, it is not clear whether this effect is also present in flavivirus-resistant mice. Further research is needed to determine how mosquito feeding impacts immune responses in different mouse strains and how this may relate to disease susceptibility in humans and livestock and poultry

What approaches could/should be taken to address the research question?

• Collection of saliva by artificial membrane feeding of vectors
• Biochemical analysis, identification and isolation of components (proteins, fatty acids and others) in vector saliva
• In vitro studies with leukocytes to determine the immunomodulatory effects of total saliva or isolated compounds from the saliva
• Study of innate and acquired immune responses of the host with or without vector infestation to understand whether or what kind of immunomodulation is induced by the vector
• Comparative studies of histology of skin biopsies of vector and non-vector infested host
• Vaccination of the host against vector factors aiding pathogen transmission or reducing host immune responses

What else needs to be done before we can solve this need?

• Knowledge of the role of vector salivary factors in pathogen transmission is needed.
• The inoculation volume required for transmission of vector-borne disease or immunomodulation of the host is not well understood.
• Further research is needed to determine the minimum volume required for transmission or immunomodulation as well as the factors that influence inoculation volume.

Existing knowledge including successes and failures

It is known that Aedes aegypti saliva alters leukocyte recruitment and cytokine signalling during West Nile virus infection, but our understanding of the specific mechanisms behind this effect is still limited. Further research is needed to identify the specific components in mosquito saliva that contribute to these changes and
how they impact disease outcomes.
Immunosuppressive effects of sialostatin L1 and L2 isolated from the taiga tick Ixodes persulcatus are known (Schulze (2020))

So, we know quite a lot about mosquito saliva that has about 100 components – mainly proteins (compared with 300 in tick saliva). Of the 100 mosquito components, we know the roles of a few, including their immunomodulatory activity (e.g., Sialokinin). In simple terms the inoculation of very small volumes of mosquito
saliva into the feeding site can have profound effects, some even lasting for days after feeding. Dendritic cells attracted to the feeding site, are often the initial target cell to establish viral infection. This means that virus delivered by a mosquito establishes an infection more efficiently than if delivered by needle. We have immunosuppressive effects of saliva, for example down regulation of Interferon. if delivered with saliva, the virus can establish more
efficiently, spread more efficiently with elevated titers and potentially more severe disease symptoms (all compared with needle inoculation).
Edwards, J.F., Higgs, S. & Beaty, B.J. (1998). Mosquito feeding-induced potentiation of Cache Valley Virus (Bunyaviridae) in mice. J. Med. Entomol. 35: 261-265.
Zeidner, N.S., Higgs, S., Happ, C.M., Beaty, B.J. & Miller, B.R. (1999).
Mosquito feeding modulates Th1 and Th2 cytokines in flavivirus susceptible mice: an effect mimicked by injection of sialokinins, but not demonstrated in flavivirus resistant mice. Parasite Immunol. 21: 35-44.
Limesand, K.H., Higgs, S., Pearson, L.D., & Beaty, B.J. (2000).
Potentiation of vesicular stomatitis New Jersey virus infection in mice by mosquito saliva. Parasite Immunol. 22: 461-467.
Limesand, K.H., Higgs, S., Pearson, L.D. & Beaty, B.J. (2003). The effect of mosquito salivary gland treatment on vesicular stomatitis New Jersey virus replication and interferon α/β expression in vitro. J. Med. Entomol. 40: 199-205.
Wanasen, N., Nussenzveig, R.H., Champagne, D.E., Soong, L. & Higgs, S. (2004). Differential modulation of murine host immune response by salivary gland extracts from the mosquitoes Aedes aegypti and Culex quinquefasciatus Med. Vet. Entomol. 2004. 18: 191-199.
Schneider, BS., L Soong, NS Zeidner, & Higgs, S. (2004). Aedes aegypti Salivary gland extracts modulate anti-viral and TH1/TH2 cytokine responses to Sindbis virus infection. Vir. Immunol. 17: 565-573.
Schneider, B.S., Soong, L., Girard, Y.A., Campbell, G., Mason, P. & Higgs, S. (2006). Potentiation of West Nile Encephalitis by mosquito feeding. Viral Immunology. 19: 74-82.
Schneider, B.S., McGee, C.E., Jordan, J.M., Stevenson, H.L., Soong, L. & Higgs, S. (2007). Prior exposure to uninfected mosquitoes enhances mortality in naturally-transmitted West Nile virus infection. PLoS ONE 2(11): e1171
Schneider, B.S. & Higgs, S. (2008). The enhancement of arbovirus transmission and disease by mosquito saliva is associated with modulation of the host immune response. Trans. Roy. Soc. Trop. Med. Hyg. 102: 400-408.
Schneider, B.S., Soong, L., Coffey, L.A., Stevenson, H.L. & Higgs, S. (2010). Aedes aegypti saliva alters leukocyte recruitment and cytokine signaling by antigen-presenting cells during West Nile virus infection. PloSONE 5: e11704. Thangamani, S., Higgs, S., Ziegler, S., Vanlandingham, D., Tesh, R. & Wikel, S. (2010). Host immune response to mosquito-transmitted chikungunya virus differs from that elicited by needle inoculated virus. PloSOne. 5:e12137.