Kristine T. Edwards

Cattle and the natural history of Rickettsia parkeri in Mississippi.

Cattle have been recognized as hosts for Amblyomma maculatum, the Gulf Coast tick, for over 100 years. For nearly as long, A. maculatum have been known to harbor the spotted fever group Rickettsia (SFGR), now known as Rickettsia parkeri. However, human infection with R. parkeri was not documented until 2004. Results presented herein describe a laboratory and a field study evaluating cattle and the natural history of A. maculatum and R. parkeri in Mississippi. In the laboratory study, seroconversion to R. parkeri antigen occurred in calves exposed to R. parkeri by injection or by feeding R. parkeri-infected A. maculatum, and two out of six animals were transiently rickettsemic. All calves remained clinically normal during the study, except for gotch ear-like lesions in all tick-infested calves, regardless of infection status of ticks, suggesting that R. parkeri is not involved in the condition. In the field study, A. maculatum (n=34) removed from Mississippi sale barn cattle (n=183) and the cattle hosts were tested for R. parkeri. Cattle were not rickettsemic by polymerase chain reaction, but 49.7% demonstrated low titers to R. parkeri antigen when tested by indirect fluorescent antibody for SFGR. Of ticks removed from cattle, 11.8% were hemolymph positive and 8.7% were indirect fluorescent antibody positive. Approximately 22% (5/23) and 4% (1/23) of harvested tick extracts were positive for R. parkeri by polymerase chain reaction of the 17 kDa antigen gene and ompA gene, respectively. An amplicon for the ompA gene from one tick was successfully sequenced and showed 100% similarity with the homologous sequence of R. parkeri. Thus, cattle may harbor R. parkeri-infected A. maculatum and produce antibodies to SFGR. Cattle may play a role in the natural history of R. parkeri infection by expanding populations of A. maculatum and transporting R. parkeri-infected ticks to various locations, rather than as a reservoir for R. parkeri.

Artificial infection of the bed bug with Rickettsia parkeri.

ABSTRACT Although a variety of disease agents have been reported from bed bugs, the mechanical and biological disease transmission potential of bed bugs remains unelucidated. In this study we assayed survivability of the mildly pathogenic spotted fever group rickettsia, Rickettsia parkeri, in bed bugs after feeding on R. parkeri-infected chicken blood. Two groups of 15 adult bed bugs each were fed on infected or noninfected blood, and two groups of fourth-instar bed bugs also were fed on either infected or noninfected blood. One group of 15 adult bed bugs received no bloodmeal and was included as an additional control. Two weeks postfeeding, two pools of five live bed bugs from each group were surface sterilized, macerated, and placed in Vero cell cultures in an attempt to grow live organism. The remaining five individual bed bugs from each group were dissected, their salivary glands were removed for immunofluorescence assay (IFA) staining, and the remaining body parts were processed for polymerase chain reaction (PCR) analysis. Results indicated that no immature (now molted to fifth instar) bed bugs were positive for R. parkeri by IFA or PCR, indicating that organisms did not survive the molting process. After 4 wk of cell culture, no organisms were seen in cultures from any of the treatment or control groups, nor were any cultures PCR positive. However, two of the adult bed bugs were IFA positive for rickettsia-like organisms, and these two specimens were also PCR positive using R. parkeri-specific primers. These IFA and PCR results indicate that remnants of Rickettsia parkeri (possibly whole organisms) survived in the bugs for 2 wk, but the viability of the organisms in these two specimens could not be determined.

Risk assessment for Helicoverpa zea (Lepidoptera: Noctuidae) resistance on dual-gene versus single-gene corn.

ABSTRACT Recent Environmental Protection Agency (EPA) decisions regarding resistance management in Bt-cropping systems have prompted concern in some experts that dual-gene Bt-corn (Cry1A.105 and Cry2Ab2 toxins) may result in more rapid selection for resistance in Helicoverpa zea (Boddie) than single-gene Bacillus thuringiensis (Bt)-corn (Cry1Ab toxin). The concern is that Bt-toxin longevity could be significantly reduced with recent adoption of a natural refuge for dual-gene Bt-cotton (Cry1Ac and Cry2Ab2 toxins) and concurrent reduction in dual-gene corn refuge from 50 to 20%. A population genetics framework that simulates complex landscapes was applied to risk assessment. Expert opinions on effectiveness of several transgenic corn and cotton varieties were captured and used to assign probabilities to different scenarios in the assessment. At least 350 replicate simulations with randomly drawn parameters were completed for each of four risk assessments. Resistance evolved within 30 yr in 22.5% of simulations with single-gene corn and cotton with no volunteer corn. When volunteer corn was added to this assessment, risk of resistance evolving within 30 yr declined to 13.8%. When dual-gene Bt-cotton planted with a natural refuge and single-gene corn planted with a 50% structured refuge was simulated, simultaneous resistance to both toxins never occurred within 30 yr, but in 38.5% of simulations, resistance evolved to toxin present in single-gene Bt-corn (Cry1Ab). When both corn and cotton were simulated as dual-gene products, cotton with a natural refuge and corn with a 20% refuge, 3% of simulations evolved resistance to both toxins simultaneously within 30 yr, while 10.4% of simulations evolved resistance to Cry1Ab/c toxin.

Bed bug saliva causes release of monocytic inflammatory mediators: plausible cause of cutaneous bite reactions.

Bed bugs may cause mild to severe cutaneous reactions. We studied the ability of bed bug salivary extract (SGE) to induce inflammatory reactions responsible for cutaneous manifestations and found that SGE stimulated the production of several potent chemokines and cytokines from macrophages. Chemokines induced by SGE included those known to recruit eosinophils (eotaxin), attract neutrophils [interleukin (IL)-8] or induce their survival and proliferation (granulocyte colony-stimulating factor). Cytokines involved in cell-mediated immunity, including IL-7, IL-10 and IL-12, were also induced. Saliva of bed bugs contains protein and non-protein molecules that have pleotropic effects on macrophages, orchestrating the immune response in the skin after bed bug bites.

Distribution of Spotted Fever Group Rickettsiae in Select Tissues of Experimentally Infected and Field-Collected Gulf Coast Ticks

ABSTRACT Salivary glands, midgut, Malpighian tubules, and ovaries were dissected from infected, colony-derived Amblyomma maculatum (Gulf Coast ticks) injected as nymphs with either Rickettsia parkeri (a spotted fever group rickettsia [SFGR] ; treatment) or phosphate-buffered saline (negative control). For comparison, similar tissues were dissected from hemolymph-positive, field-collected ticks. Tissues were analyzed by indirect fluorescent antibody (IFA) tests. All phosphate-buffered saline-injected ticks were IFA negative, whereas SFGR were detected by IFA in 100% of the salivary glands and ovaries and 78 and 75% of midgut and Malpighian tubule samples, respectively, of R. parkeri-injected ticks. Nearly 22% (10/46) of the field-collected ticks were hemolymph positive. Of those, SFGR were detected by IFA in 80% of the salivary glands, 67% of the ovaries, and 60% in the midgut and Malpighian tubules. This is the first study to assess the distribution of SFGR in select tissues of A. maculatum ticks.

Impact of Insect Management on Population Dynamics and Insecticide Resistance of Tarnished Plant Bug (Hemiptera: Miridae).

While transgenic plants targeting lepidopteran and coleopteran insects have been available for almost 20 yr, there are no transgenic crops that target hemipteran insects such as tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), though at least one company lists potential products in advanced stages of development. A resistance management model for the U.S. Mid-South was developed to aid in resistance risk assessments for transgenic crops targeting L. lineolaris, and validated against the prior case of pyrethroid resistance in this insect. The model predicted that resistance to a pyrethroid would evolve in 17.6-21.0 yr (depending on the initial resistance allele frequency), which was close to the 15-20 years observed in the field. Due to uncertainty in female fecundity, we varied fecundity from 3 eggs/female/day to 12 eggs/female/day. Sprays were applied based on action thresholds, and increasing fecundity therefore increased the number of sprays applied per year and decreased durability. We also varied the action threshold in cotton (Gossypium hirsutum L.) fields (the population levels at which sprays were applied) from 17,600/ha to as low as 1,100/ha. Lowering the threshold increased the number of sprays applied, but also increased durability of the pesticide. Removing the noncotton host refuge present at the same time as cotton changed the relationship so that increasing the action threshold increased durability. The impact of insect resistance management on action threshold cost estimates will vary depending on the landscape, and cannot be assumed to always move the economic injury level in the same direction.

Gotch Ear in a Goat: A Case Report

A 1-year-old castrated male Saanen goat was observed to have drooping and edema of the left ear consistent with published accounts of gotch ear in cattle associated with a tick bite. The goats left ear was edematous from the tip of the pinna to the base of the ear. No signs of trauma or infectious processes were observed. Three engorged Gulf Coast ticks (Amblyomma maculatum) were observed attached inside the ear. Ticks were removed and the ear biopsied at tick attachment sites. The affected ear was treated topically with betadine after removal of the ticks. No other treatment was administered. The goat remained free of clinical signs and the edema of the ear resolved within 3 days after tick removal. No clinical adverse effects of the condition were evident. All three ticks were positive for spotted fever group rickettsia by polymerase chain reaction analysis and showed 100% similarity with the homologous sequence of Rickettsia parkeri. There was no immunohistochemical evidence of spotted fever group rickettsia in the ear samples, supporting the hypothesis that gotch ear is not due to rickettsial infection. This report represents the first apparent case of gotch ear in a goat.

Survey of Mosquito Control Knowledge, Attitudes, and Practices among County and Municipal Programs in Mississippi

Abstract After Hurricane Katrina, 87 qualifying communities in Mississippi were issued contracts for disbursement of

Effects of Bed Bug Saliva on Human Skin

2.8 million in federal funds for mosquito control. As part of this funding, a survey of mosquito control personnel was conducted to evaluate effectiveness of mosquito control programs at these 87 sites before and after disbursement of funds. Two nearly identical questionnaires requested information from county and municipal personnel about specifics for each of the sites, descriptions of operations and practices, information about mosquito control personnel, and information about attitudes of the respondents before and after implementation of the grant. Findings revealed that municipal mosquito control in Mississippi is conducted mostly by personnel in small town/city public works departments and not by contract to an outside agency. Also, mosquito control is composed mostly of routine spraying, based loosely on complaints, time of year, or other factors. For example, only 3% of participants in our survey utilized adult mosquito trapping surveillance data in their spray decisions, and only 11% said they dipped for larvae before treating standing water sites. In light of current environmental consciousness and chemophobia, much work remains to bring Mississippi mosquito control up to current scientific standards. The survey described herein was the first step, shedding light on specific problems encountered in mosquito control and providing public health and regulatory officials with guidance as to which issues to address first.