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Submitted to: World Association for the Advancement of Veterinary Parasitologists
Publication Type: Abstract Only Publication Acceptance Date: 3/20/2019 Publication Date: N/A Citation: N/A Interpretive Summary: Ticks, mosquitoes, sand flies, and other arthropod pests transmit disease causing agents to animals and humans. The resulting vector-borne diseases constitute 17% of all infectious disease worldwide. Transmission and progression of clinical illness for many of these vector-borne diseases can be facilitated by saliva of the pest vectors. We previously reported that tick saliva contains an enzyme (acetylcholinesterase, AChE) that destroys the chemical neurotransmitter, acetylcholine. Acetylcholine is known to participate in early stages of immune cell activation and response to tissue damage or presence of disease causing agents. We proposed that the tick salivary acetylcholinesterase injected into the host at the tick bite site might alter the immune response in a manner that promoted survival and development of the disease-causing agents. We further reasoned that other vectors of disease might also contain salivary AChE that could help them transmit disease-causing agents. We found AChE-like enzyme activity in saliva of several species of ticks, mosquitoes, sand flies, and possibly biting midges, all of which are known to exhibit salivary-assisted transmission of vector-borne disease agents. These results are consistent with a key role of the salivary AChE in transmission of vector-borne diseases, and provide new knowledge to guide further research to elucidate the mechanism(s) responsible for vector-borne disease, potentially leading to methods to reduce disease transmission and impact. Technical Abstract: Arthropod vectors transmit pathogens responsible for 17% of all infectious diseases globally. Most of these pathogens are transmitted through the vector’s saliva during blood feeding. Ticks transmit bacteria, viruses, and protozoans, and in some parts of the world are more important than mosquitoes as vectors of zoonotic diseases affecting humans. The southern cattle fever tick, Rhipicephalus microplus, is the most economically important ectoparasite of cattle worldwide. Our previous research documenting the presence of acetylcholinesterase (AChE) in the saliva of R. microplus proposed this enzymatic activity could: 1) decrease the toxicity of acetylcholine in the blood meal, 2) modulate host immune responses to facilitate tick parasitism, and 3) facilitate salivary assisted transmission (SAT). We hypothesized further that if tick salivary acetylcholinesterase participates in pathogen SAT then similar enzymatic activity would be present in the saliva of other arthropod vectors. This reports includes evidence of AChE-like activity in the saliva of several ticks, mosquitoes, sand flies, and apparently biting midges. Salivary AChE-like activity was not detected in the horn fly, stable fly, or house fly. Salivary cholinesterase (ChE) activities detected in arthropod vectors exhibited Michaelis-Menten KM values lower than the KM value for bovine serum AChE. A lower KM value is indicative of higher affinity for substrate, and is consistent with a hypothesized role in localized depletion of host tissue acetylcholine and modulation of host immune responses at the vector bite site that might favor hematophagy, which could enable infection by vector-borne pathogens. |
