Kimberly H. Lohmeyer

One Health approach to identify research needs in bovine and human babesioses: workshop report

BackgroundBabesia are emerging health threats to humans and animals in the United States. A collaborative effort of multiple disciplines to attain optimal health for people, animals and our environment, otherwise known as the One Health concept, was taken during a research workshop held in April 2009 to identify gaps in scientific knowledge regarding babesioses. The impetus for this analysis was the increased risk for outbreaks of bovine babesiosis, also known as Texas cattle fever, associated with the re-infestation of the U.S. by cattle fever ticks.ResultsThe involvement of wildlife in the ecology of cattle fever ticks jeopardizes the ability of state and federal agencies to keep the national herd free of Texas cattle fever. Similarly, there has been a progressive increase in the number of cases of human babesiosis over the past 25 years due to an increase in the white-tailed deer population. Human babesiosis due to cattle-associated Babesia divergens and Babesia divergens-like organisms have begun to appear in residents of the United States. Research needs for human and bovine babesioses were identified and are presented herein.ConclusionsThe translation of this research is expected to provide veterinary and public health systems with the tools to mitigate the impact of bovine and human babesioses. However, economic, political, and social commitments are urgently required, including increased national funding for animal and human Babesia research, to prevent the re-establishment of cattle fever ticks and the increasing problem of human babesiosis in the United States.

Evidence for role of white-tailed deer (Artiodactyla: Cervidae) in epizootiology of cattle ticks and southern cattle ticks (Acari: Ixodidae) in reinfestations along the Texas/Mexico border in south Texas: a review and update.

ABSTRACT From 1907 when the fever tick eradication campaign began until 1933, the tick eradication methods of dipping cattle in an acaricide or “pasture vacation” were enormously successful in eradicating southern cattle ticks [Rhipicephalus (Boophilus) microplus (Canestrini) ], until failures began to occur in some areas of Florida. Regarding the failures in Florida, the consensus was that populations of white-tailed deer [Odocoileus virginianus (Zimmermann)] infested with southern cattle ticks were responsible. After numerous deer in several counties were killed, eradication was achieved in Florida. As in Florida, in Texas increasing numbers of failures of the pasture vacation approach to tick eradication from the 1970s to the present are known to be related to the abundance of white-tailed deer and perhaps other wild ungulate species. A sizable body of evidence confirms the hypothesis that white-tailed deer support the dispersal and maintenance of both cattle ticks [Rhipicephalus (Boophilus) annulatus (Say)] and southern cattle ticks (cattle fever ticks) within the permanent quarantine or buffer zone in South Texas along the Rio Grande, as well as in the so-called free (“cattle fever tick-free”) area north and east of the buffer zone and extending to the east coast of the United States. As of August 2009, in addition to the permanent quarantine zone of ≈2,233 km2, three temporary preventative or blanket quarantines were established. Currently, only two methodologies exist to control ticks feeding on white-tailed deer: 1) a systemic treatment method involving dispersal of ivermectin-medicated corn, Zea mays L.; and 2) two topical treatment methods, ‘4-poster’ deer treatment bait stations and ‘2-poster’ deer treatment feeder adapters, both of which passively apply topically active acaricide to deer for the eradication of populations of cattle fever tick associated with white-tailed deer. This study presents and summarizes confirmational support for the role of white-tailed deer derived from historical accounts, circumstantial evidence from review of recent infestations, and cattle fever tick infestations on white-tailed deer that were live-captured and examined specifically for cattle fever ticks.

Analysis of expressed sequence tags from a significant livestock pest, the stable fly (Stomoxys calcitrans), identifies transcripts with a putative role in chemosensation and sex determination.

The stable fly, Stomoxys calcitrans L. (Diptera: Muscidae), is one of the most significant pests of livestock in the United States. The identification of targets for the development of novel control for this pest species, focusing on those molecules that play a role in successful feeding and reproduction, is critical to mitigating its impact on confined and rangeland livestock. A database was developed representing genes expressed at the immature and adult life stages of the stable fly, comprising data obtained from pyrosequencing both immature and adult stages and from small-scale sequencing of an antennal/maxillary palp-expressed sequence tag library. The full-length sequence and expression of 21 transcripts that may have a role in chemosensation is presented, including 13 odorant-binding proteins, 6 chemosensory proteins, and 2 odorant receptors. Transcripts with potential roles in sex determination and reproductive behaviors are identified, including evidence for the sex-specific expression of stable fly doublesex- and transformer-like transcripts. The current database will be a valuable tool for target identification and for comparative studies with other Diptera.

Survival and fate of Salmonella enterica serovar Montevideo in adult horn flies (Diptera: Muscidae).

ABSTRACT Contamination of cattle peripheral lymph nodes with Salmonella enterica is proposed to occur via a transdermal route of entry. If so, bacteria may be introduced to cattle by biting arthropods. Biting flies, such as horn flies (Haematobia irritans irritans (L.)) (Diptera: Muscidae), are intriguing candidates for transmitting Salmonella to cattle because they provide a route of entry when they breach the skin barrier during blood feeding. Using a green fluorescent protein-expressing strain of Salmonella Montevideo (S. Montevideo-GFP), the current study demonstrated that horn fly grooming subsequent to tactile exposure to the bacteria resulted in acquisition of the bacteria on mouthparts as well as microbial ingestion. Consumption of a bloodmeal containing ≈102, ≈104, or ≈106 S. Montevideo-GFP resulted in horn fly colonization for up to 72 h postingestion (PI). Epifluorescent microscopy indicated that the bacteria were not localized to the crop but were observed within the endoperitrophic space, suggesting that regurgitation is not a primary route of transmission. S. Montevideo-GFP were cultured from excreta of 100% of flies beginning 6–7 h PI of a medium or high dose meal and >12 h PI in excreta from 60% of flies fed the low-dose meal. Animal hides and manure pats are sources for horn flies to acquire the Salmonella and mechanically transmit them to an animal while feeding. Mean quantities of 5.65- 67.5 × 102 CFU per fly were cultured from fly excreta passed within 1 d after feeding, suggesting the excreta can provide an additional microbial source on the animals hide.

Laboratory evaluation of novaluron as a development site treatment for controlling larval horn flies, house flies, and stable flies (Diptera: Muscidae).

ABSTRACT A granular formulation of novaluron (Novaluron 0.2G, 0.2% [AI]), a newer benzoylphenyl urea insecticide, was evaluated for its efficacy in controlling the larval stage of horn flies, Haematobia irritans (L.); house flies, Musca domestica L.; and stable flies, Stomoxys calcitrans (L.), in cow manure. Various rates and insecticide placement locations (top, middle, and bottom of manure) were evaluated in this study and all combinations of these variables reduced adult emergence of all three species when compared with the untreated controls. The presence of deformed pupae indicated that novaluron had an insect growth regulator effect on the developing fly larvae. Top, middle, or bottom application rates of 0.125, 0.195, 0.25, and 0.375 g novaluron onto manure samples, reduced adult horn fly emergence by >90%. Middle and bottom application rates of 0.195, 0.25, and 0.375 g novaluron reduced adult house fly emergence >93%. All rates and placement combinations resulted in >98% reduction of adult stable fly emergence. The level of control efficacy observed against these three fly species along with the ease of use of a granular formulation, make this product an ideal candidate for use in an integrated livestock pest management program.

Dynamics and mechanisms of permethrin resistance in a field population of the horn fly, Haematobia irritans irritans

A study was conducted at the Pressler ranch, near Kerrville, Texas, USA between 2002 and 2006 to determine the dynamics and mechanisms of resistance to permethrin in a field population of the horn fly, Haematobia irritans irritans (L.). Changes of resistance to pyrethroid insecticide associated with use of a pour‐on formulation of cyfluthrin in 2002 and use of diazinon ear tags in subsequent years were studied using a filter paper bioassay technique and a polymerase chain reaction assay that detects two sodium channel mutations, kdr and super‐kdr resistance alleles. A maximum of 294‐fold resistance to permethrin was observed in the summer of 2002. A significant decrease in the resistance level was observed in spring 2003, and resistance continued to decline after animals were treated with diazinon ear tags. In response to pyrethroid treatments, the allelic kdr and super‐kdr frequency increased from 56.3% to 93.8% and from 7.5% to 43.8%, respectively in 2002, and decreased significantly in 2003 when the pyrethroid insecticide was no longer used to treat animals. Females were found to have a higher allelic super‐kdr frequency than males in 2002, while no difference was detected between males and females in the allelic kdr frequency. There was a significant positive correlation between frequencies of the sodium channel mutations and levels of permethrin resistance, suggesting that the sodium channel mutations, kdr and super‐kdr, are the major mechanisms of resistance to pyrethroids in this horn fly population. Results of synergist bioassays also indicated possible contributions of two metabolic detoxification mechanisms, the mixed function oxidases (MFO) and glutathione S‐transferases (GST). Compared to a horn fly infestation of an untreated herd, treatments with the pyrethroid pour‐on formulation failed to control horn flies at the Pressler ranch in 2002. Sustained control of horn flies was achieved with the use of diazinon ear tags in 2003 and subsequent years.

Effects of pyriproxyfen and buprofezin on immature development and reproduction in the stable fly

The stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), is one of the most significant biting flies that affect cattle. The use of traditional insecticides for stable fly control has only a limited success owing to the insects unique feeding behaviours and immature development sites. A laboratory study was conducted to evaluate the effects of two insect growth regulator (IGR) products, pyriproxyfen and buprofezin, on the development of the immature stages of the stable fly and the effects of pyriproxyfen on oviposition and egg hatch. Both pyriproxyfen and buprofezin had significant inhibitory effects on immature development. The LC50s of pyriproxyfen and buprofezin were 0.002 and 18.92 p.p.m., respectively. Topical treatment of adult females with different doses of pyriproxyfen had significant negative effects on both female oviposition and egg hatching when 1‐ and 3‐day‐old females were treated, and the effects were dose dependent. A significant reduction in the mean number of eggs laid was observed only at the highest pyriproxyfen dose (8 µg/fly) and egg hatch was unaffected by pyriproxyfen treatment when 5‐day‐old females were treated. Results from the present study indicate that pyriproxyfen has the potential to be used as part of an integrated stable fly management programme.

Efficacy of Amitraz-Impregnated Collars on White-Tailed Deer (Artiodactyla: Cervidae) in Reducing Free-Living Populations of Lone Star Ticks (Acari: Ixodidae)

ABSTRACT Over a 7 yr period, we monitored the effect of a commercially available, amitraz impregnated anti-tick collar in controlling free-living populations of lone star ticks, Amblyomma americanum (L.) when manually fitted around necks of white-tailed deer, Odocoileus virginianus (Zimmermann). Study animals in treatment and control groups were confined in 38.8 ha game-fenced and densely vegetated treatment plots in South Texas. Tick densities during years 1 and 7 served as untreated pre- and posttreatment comparisons and treatments occurred during years 2 through 5. Reductions in tick densities in the treatment plot were compared against tick densities in a control plot having similar vegetation and numbers of untreated deer. During years of treatment, indices of control pressure ranged from 18.2 to 82.6 for nymphs and 16.9–78.7 for adults, and efficacy, expressed as percentage control during the final year of treatment, was 77.2 and 85.0%, respectively, for nymphal and adult ticks. These data show that acaricidal collar treatments provide efficacies very similar to those achieved with the existing ivermectin-medicated bait and ‘4-Poster’ topical treatment technologies to control ticks feeding on wild white-tailed deer.

Assessing Transmission of Salmonella to Bovine Peripheral Lymph Nodes upon Horn Fly Feeding

Biting arthropods are implicated in the transdermal transmission of Salmonella to bovine peripheral lymph nodes, and such contamination can contribute to increased Salmonella prevalence in processed beef. Since horn flies can acquire Salmonella and then excrete the bacteria in their feces, on-animal fly infestations were conducted in this study to assess whether horn flies have a role in this bacterial transmission. Three Salmonella serotypes were used to assess fly acquisition from and excretion onto cattle. The results indicated that flies can acquire Salmonella from the hide, as assessed by recovery from homogenates of surfacesterilized flies, and that Salmonella persists for at least 5 days in the fly. Fly fecal excreta serves as a bacterial contaminant on the hide, and the overall mean probable estimate of the quantity shed was ≈10(5) most probable number per fly cage area. In 5 days, no transmission of the bacteria to bovine peripheral lymph nodes was evident, prompting an assessment of the effects of prolonged horn fly feeding on transmission. Three groups of animals were infested with flies that had consumed a blood meal containing Salmonella Senftenberg. After 5 days, the study was either terminated or the flies were removed and the cages replenished with unfed flies either once or twice over the course of an 11- or 19-day fly exposure period, respectively. A microlancet-inoculated positive-control animal was included in each group for comparison. The impact of prolonged horn fly feeding was evident, as 8% of lymph nodes cultured were positive from the 5-day exposure, whereas 50 and 42% were positive from 11- and 19-day exposures, respectively. Higher concentrations of Salmonella were recovered from fly-infested animals than from the microlancet-inoculated control, likely a result of repeated inoculations over time by flies versus a single introduction. The data described provide new insights into the transmission dynamics of Salmonella in cattle populations, highlighting a role for biting flies as an important reservoir.

Effects of Photoperiod on Reproduction, Nymphal Developmental Timing, and Diapause in Amblyomma maculatum (Acari: Ixodidae)

ABSTRACT Female engorgement weight, oviposition, and molting times of larvae and nymphs of Amblyomma maculatum Koch (Acari: Ixodidae) were studied at various photoperiods under constant humidity and temperature in the laboratory. Ticks were held at photoperiods of 0:24, 10:14, 12:12, or 14:10 (L:D) h from egg through unfed nymphal stage and then at either the same or a different regime from fed nymphs to adults. No significant effects were observed on oviposition, female engorgement weights, survival, or molting time to unfed nymphs. Nymphal molting times were significantly shorter at the short-day regime (10:14) during the larval stage and 12:12 during the nymphal stage compared with those held at either 14:10 during both life periods or at 0:24 during both life periods. Longer molting times also were observed in ticks held at 12:12 during the larval phase and either 10:14, 12:12, or 0:24 during the nymphal phase compared with 14:10 during both life periods or 0:24 during both life periods. Ticks held at 10:14 during the larval phase and at 0:24 or 10:14 had longer molting times compared with those at 14:10 or 0:24 during both life periods. No differences in survival to either nymphal or adult stages were observed at any regime, and at day 25 no individuals were observed to be in developmental diapause. This study demonstrates that developmental diapause does not seem to be photoperiodically induced in fed nymphal A. maculatum in the laboratory.