Connor Rich

Hematophagous arthropods and associated pathogens are becoming more prevalent globally. With limited treatment options, prevention is the top priority to reduce disease. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) has emerged as a standard detection method for many laboratories, but it has several drawbacks. Degraded sample quality, failed RNA preparations, and the presence of reaction inhibitors can lead to false negative results, introducing the need for a positive control. Existing control methods rely on adding exogenous nucleotides during amplification reactions, which may not reflect the quality of the sample. Incorporating assays to detect endogenous mosquito mRNA transcripts provides assurance that sample quality is sufficient for the downstream amplification of pathogen RNA. In the present study, we applied the Rapid Amplification of cDNA Ends (RACE) technique to obtain a full-length calreticulin cDNA sequence from the Culex restuans mosquito, collected in Massachusetts, USA. We then used the newly discovered cDNA sequence to design primers and probes spanning the first exon–exon junction of the calreticulin gene, which allowed for specific and accurate RNA transcript detection in an RT-qPCR assay. This assay detected the presence of calreticulin transcripts in extracted pools of mosquito RNA. This approach may be further developed to include other relevant mosquito species and, with extensive validation, may have potential for use as an endogenous control in arbovirus surveillance.

Deer keds (Lipoptena spp. and Neolipoptena ferrisi) are hematophagous ectoparasites that primarily infest white-tailed deer (Odocoileus virginianus) and other cervids in the United States. The distribution of deer keds in the northeastern United States and the pathogens they harbor remains relatively unexplored. In this study, we examined the geographical distribution and pathogen prevalence of deer keds in Massachusetts by collecting samples from white-tailed deer and testing for tick-borne pathogens. Deer keds were collected across the state, including in four previously unrecorded counties, indicating a wide distribution. Pathogen screening revealed the presence of Anaplasma phagocytophilum DNA in 30% of the keds, but no other pathogens were detected. The medical and biological significance of detecting A. phagocytophilum DNA in deer keds requires future studies. This research provides a baseline for the distribution and pathogen prevalence of deer keds in Massachusetts and highlights the potential of deer keds as sentinels for monitoring deer-associated microbes.

Borrelia burgdorferi’s inosine-5′-monophosphate dehydrogenase (IMPDH, GuaB encoded by the guaB gene) is a potential therapeutic target. GuaB is necessary for B. burgdorferi replication in mammalian hosts but not in standard laboratory culture conditions. Therefore, we cannot test novel GuaB inhibitors against B. burgdorferi without utilizing mammalian infection models. This study aimed to evaluate modifications to a standard growth medium that may mimic mammalian conditions and induce the requirement of GuaB usage for replication. The effects of two GuaB inhibitors (mycophenolic acid, 6-chloropurine riboside at 125 μM and 250 μM) were assessed against B. burgdorferi (guaB+) grown in standard Barbour–Stoenner–Kelly-II (BSK-II) medium (6% rabbit serum) and BSK-II modified to 60% concentration rabbit serum (BSK-II/60% serum). BSK-II directly supplemented with adenine, hypoxanthine, and nicotinamide (75 μM each, BSK-II/AHN) was also considered as a comparison group. In standard BSK-II, neither mycophenolic acid nor 6-chloropurine riboside affected B. burgdorferi growth. Based on an ANOVA, a dose-dependent increase in drug effects was observed in the modified growth conditions (F = 4.471, p = 0.001). Considering higher drug concentrations at exponential growth, mycophenolic acid at 250 μM reduced spirochete replication by 48% in BSK-II/60% serum and by 50% in BSK-II/AHN (p < 0.001 each). 6-chloropurine riboside was more effective in both mediums than mycophenolic acid, reducing replication by 64% in BSK-II/60% serum and 65% in BSK-II/AHN (p < 0.001 each). These results demonstrate that modifying BSK-II medium with physiologically relevant levels of mammalian serum supports replication and induces the effects of GuaB inhibitors. This represents the first use of GuaB inhibitors against Borrelia burgdorferi, building on tests against purified B. burgdorferi GuaB. The strong effects of 6-chloropurine riboside indicate that B. burgdorferi can salvage and phosphorylate these purine derivative analogs. Therefore, this type of molecule may be considered for future drug development. Optimization of this culture system will allow for better assessment of novel Borrelia-specific GuaB inhibitor molecules for Lyme disease interventions. The use of GuaB inhibitors as broadcast sprays or feed baits should also be evaluated to reduce spirochete load in competent reservoir hosts.

Borrelia burgdorferi ’s Inosine-5’-Monophosphate dehydrogenase (IMPDH, GuaB) is a potential therapeutic target. GuaB is not needed for B. burgdorferi survival and replication in standard growth media, therefore our ability to test novel drugs against the whole organism is limited to tests using mammalian hosts. Modifications to standard culture conditions that can induce borreliastatic effects of GuaB inhibitors will enhance our ability to evaluate these inhibitors. This study aimed to evaluate basic modifications to standard growth media that can achieve this objective. Effects of GuaB inhibitors (mycophenolic acid, 6-Chloropurine) were compared in standard Barbour-Stoenner-Kelly-II (BSK-II) medium with BSK-II modified to 60% concentration rabbit serum, using B. burgdorferi 5A1. Effects were also evaluated with another BSK-II modification with the direct supplementation of hypoxanthine, adenine, and nicotinamide (75 μM each). In standard BSK-II, neither mycophenolic acid nor 6-Chloropurine riboside affected B. burgdorferi growth. An ANOVA showed significant, dose-dependent interactions between culture condition and treatment considering modified growth conditions (F = 4.471, P = 0.001). Mycophenolic acid at 250 μM reduced replication by 48 and 50% (P < 0.001 each). 6-Chloropurine riboside was more effective in both conditions at 250 μM, reducing growth by 64 and 65% (P < 0.001 each). Effects of GuaB inhibitors were shown against whole organism Borrelia burgdorferi for the first time. Modification of BSK-II medium with physiologically relevant levels of mammalian serum supports replication and induces GuaB inhibitor-mediated suppression of replication. Effects of 6-Chloropurine riboside were demonstrated for the first time, indicating that B. burgdorferi can salvage and phosphorylate these analogue purine derivatives. These molecules can be manipulated to better inhibit replication. Optimisation will allow the assessment of novel Borrelia-specific IMPDH inhibitor molecules in culture for Lyme disease interventions. Highlights: Effects of IMPDH inhibitors are shown against whole organism Borrelia burgdorferi for the first time. Modification of BSK-II medium with physiologically relevant levels of mammalian serum supports replication and induces IMPDH inhibitor-mediated suppression of replication. Effects of 6-Chloropurine riboside are demonstrated for the first time, indicating that B. burgdorferi can salvage and phosphorylate these analogue purine derivatives. These molecules can be manipulated to better inhibit replication. Optimisation of modified BSK-II will allow the assessment of novel Borrelia -specific IMPDH inhibitor molecules in culture for Lyme disease interventions.

Reservoir host associations have been observed among and within Borrelia genospecies, and host complement-mediated killing is a major determinant in these interactions. In North America, only a subset of Borrelia burgdorferi lineages cause the majority of disseminated infections in humans. We hypothesize that differential resistance to human complement-mediated killing may be a major phenotypic determinant of whether a lineage can establish systemic infection. As a corollary, we hypothesize that borreliacidal action may differ among human subjects. To test these hypotheses, we isolated primary B. burgdorferi clones from field-collected ticks and determined whether the killing effects of human serum differed among those clones in vitro and/or whether these effects were consistent among human sera. Clones associated with human invasiveness did not show higher survival in human serum compared to noninvasive clones. These results indicate that differential complement-mediated killing of B. burgdorferi lineages is not a determinant of invasiveness in humans. Only one significant difference in the survivorship of individual clones incubated in different human sera was detected, suggesting that complement-mediated killing of B. burgdorferi is usually similar among humans. Mechanisms other than differential human complement-mediated killing of B. burgdorferi lineages likely explain why only certain lineages cause the majority of disseminated human infections.