Effect of low temperature and relative humidity on reproduction and survival of the tick Rhipicephalus microplus

Two protocols using fluralaner for Rhipicephalus microplus strategic control on taurine cattle in a tropical region

BACKGROUND

The present study aimed to evaluate the effects of different treatment strategies using a new commercial formulation containing pour-on fluralaner on Rhipicephalus microplus infestation in cattle and in pastures in a tropical climate region where up to five generations of this tick species can occur per year.

METHODS

Forty-five naturally infested cattle were divided into three experimental groups: T01, treated with fluralaner (2.5 mg/kg) pour-on every 42 days; T02, the cattle received the first treatment with fluralaner on Day 0 but the next treatment involved a weekly visual evaluation; T03, control, received palliative treatment with a spray formulation when the group mean was ≥ 30 ticks. Counts of female R. microplus were performed weekly until day 343, and larval counts on pasture were performed on Days 0, 30, and 60 and every 30 days until Day 330.

RESULTS

Using fluralaner, six applications were performed in Group T01, and four were performed in Group T02. In the control group (T03), it was necessary to perform eight palliative acaricide treatments with the spray formulation. The animals in T01 and T02 showed lower mean tick counts (p ≤ 0.05) than the control group (T03) on 28 and 27 of the 49 evaluated dates, respectively. In the paddock where the animals were kept as controls, the R. microplus larvae counts increased to 1458. In the paddocks where the animals were treated with fluralaner, the number was ≤ 19 per paddock during the study.

CONCLUSIONS

The different strategic treatment protocols performed with pour-on fluralaner (2.5 mg/kg) over a year in taurine cattle in a tropical region with a history of up to five annual generations of cattle ticks were effective, maintaining levels of R. microplus infestations in animals and in pastures close to zero in most of the study. Depending on the retreatment criterion adopted, the number of applications per year may be lower, resulting in a reduction in the mean cost of acaricide treatment per year and lower exposure of R. microplus populations to the active ingredient, resulting in lower resistance and selection pressure.

Widespread acaricide resistance and multi-resistance in Rhipicephalus microplus in Ecuador and associated environmental and management risk factors

Rhipicephalus microplus is a cattle tick widely distributed in tropical and subtropical areas. Various acaricides are used and applied to control the ticks, but resistance is common. The objectives of this study were to evaluate the spatial distribution of resistance to the most commonly applied acaricides (amitraz, ivermectin, and alpha-cypermethrin) in ticks and assess potential risk factors associated with tick resistance in a strip between ±0.5° latitude of the continental part of Ecuador. Larval package tests were used to evaluate the level of acaricide resistance in 96 cattle farms. The association between 11 farm management and 8 ecological variables and acaricide resistance and multi-resistance was evaluated. Dose-response models were used to study the level of resistance. 72 % (69/96), 70 % (67/96), and 64 % (61/96) of farms had ticks resistant to amitraz, ivermectin, and alpha-cypermethrin, respectively. Multi-resistance was also widespread. Larger herds and dairy farms had a significantly higher probability of resistance for three commonly used acaricides. Environmental factors related to rainfall were also associated with acaricidal resistance presence. Ivermectin resistance was associated with use of the acaricide (OR = 8.9909; 7.7519-10.2300), mean temperature (OR = 1.3205;1.0742-1.6799)), and inversely associated with paddock rotation (OR = 0.1753; 0.0294-0.7836), and precipitation of the wettest month (BIO13) (OR = 0.9903; 0.9839-0.9957); amitraz with use of the acaricide (OR = 4.3934; 3.3679-5.4188), precipitation seasonality (BIO15) (OR=0.9742; 0.9542-0.9925), and precipitation (OR = 0.9995; 0.9994-0.9999); and alpha-cypermethrin with precipitation (OR=0.9995; 0.9990-0.9999) and use of the acaricide (OR = 14.4597; 13.4343-15.4852). In conclusion, acaricide resistance was widespread in our study area. Better-integrated tick management and environmentally friendly control strategies are required to reduce the use of acaricides while limiting tick-associated damage in herds.

Differences in the reproductive output and larval survival of Rocky Mountain wood ticks (Dermacentor andersoni) and American dog ticks (Dermacentor variabilis) from prairie populations near their northern distributional limits in western Canada

The effects of temperature and relative humidity (RH) on female reproductive output, egg development and larval survival were determined for Rocky Mountain wood ticks (Dermacentor andersoni) from a prairie population (Chin Lakes, Alberta, Canada) near the northern distribution limit of this species. The responses of D. andersoni eggs and unfed larvae to different temperature (25 or 32 °C) and RH (35, 55, 75, 85 or 95%) regimes were compared to our previously published data (Diyes et al. 2021) for a northern prairie population of American dog ticks (Dermacentor variabilis). Oviposition by D. andersoni females took 21-30 days at 25 °C and 95% RH compared to 10-21 days for D. variabilis. The number of eggs laid by female ticks was strongly dependent on their engorgement weight, and D. andersoni females produced more eggs than D. variabilis females of an equivalent body weight. Eggs of D. andersoni took less time to develop at 32 °C than 25 °C with ≥ 85% RH, and hatched faster than those of D. variabilis. Larval survival times declined as temperature increased and RH decreased, but D. andersoni survived longer at 32 °C and ≤ 75% RH than D. variabilis. The interspecific differences in responses to the same temperature and humidity regimes indicate that D. andersoni is xerophilic, whereas D. variabilis is hydrophilic. Hence, 'prairie' populations of the Rocky Mountain wood tick occur in the drier grassland ecoregions but are absent in Aspen Parklands Ecoregion which is located to the north and east of the distributional range of D. andersoni.

Protein regulation mechanism of cold tolerance in Haemaphysalis longicornis

Ticks are external parasitic arthropods that can transmit a variety of pathogens by sucking blood. Low-temperature tolerance is essential for ticks to survive during the cold winter. Exploring the protein regulation mechanism of low-temperature tolerance of Haemaphysalis longicornis could help to explain how ticks survive in winter. In this study, the quantitative proteomics of several tissues of H. longicornis exposed to low temperature were studied by data independent acquisition technology. Totals of 3 699, 3 422, and 1 958 proteins were identified in the salivary gland, midgut, and ovary, respectively. The proteins involved in energy metabolism, cell signal transduction, protein synthesis and repair, and cytoskeleton synthesis changed under low-temperature stress. The comprehensive analysis of the protein regulation of multiple tissues of female ticks exposed to low temperature showed that maintaining cell homeostasis, maintaining cell viability, and enhancing cell tolerance were the most important means for ticks to maintain vital signs under low temperature. The expression of proteins involved in and regulating the above cell activities was the key to the survival of ticks under low temperatures. Through the analysis of a large amount of data, we found that the expression levels of arylamine N-acetyltransferase, inositol polyphosphate multikinase, and dual-specificity phosphatase were up-regulated under low temperature. We speculated that they might have important significance in low-temperature tolerance. Then, we performed RNA interference on the mRNA of these 3 proteins, and the results showed that the ability of female ticks to tolerate low temperatures decreased significantly.

Microsclerotial pellets of Metarhizium spp.: thermotolerance and bioefficacy against the cattle tick

The cattle tick, Rhipicephalus microplus (Acari: Ixodidae), is a multi-billion dollar ectoparasite of global importance affecting beef and milk production. Submerged cultures of cosmopolitan entomopathogenic fungal species of the genus Metarhizium typically produce microsclerotia that provide both long-term survival and environmental resistance. Microsclerotia hold great potential as an unconventional active propagule to control this tick under laboratory and semi-field conditions. However, heat stress caused especially by elevated temperatures poses a critical environmental constraint for the successful development and efficacy of microsclerotia under tropical conditions. First, we screened six strains of Metarhizium anisopliae, Metarhizium robertsii and Metarhizium humberi for their ability to produce microsclerotia by submerged liquid cultivation. In addition, we assessed the biological fitness and bioefficacy of dried microsclerotial pellets under amenable (27 °C) and heat-stressed (32 °C) incubation against engorged adult females of R. microplus. Microsclerotia in pelletized formulation prepared with carriers based on diatomaceous earth and microcrystalline cellulose exhibited conidial production at different extents according to the fungal strain and the incubation temperature, but most strains displayed reduced sporogenesis when exposed to 32 °C. Engorged tick females exposed to sporulated microsclerotia from pelletized M. anisopliae CG47 or IP 119 had fewer number of hatching larvae in comparison to the control group, irrespective of the incubation temperature tested. The minimum dosage of microsclerotial pellets that effectively reduced hatchability of tick larvae was estimated to be 2 mg per plate (equivalent to 6.0 kg per hectare). Metarhizium microsclerotial pellets exhibited significant tolerance to 32 °C and pronounced acaricidal activity against this economically important ectoparasite of cattle, even under simulated environmental heat stress. KEY POINTS: • Heat stress affects conidial production by microsclerotia of most pelletized Metarhizium strains • Heat stress does not impair the acaricidal performance of pelletized microsclerotia • Pellet formulation of Metarhizium microsclerotia is a promising mycoacaricide.

Genetic characterization of genes encoding the major surface proteins of Anaplasma marginale from cattle isolates in Thailand reveals multiple novel variants

Bovine anaplasmosis is a serious tick-borne disease that is responsible for economic loss worldwide. The major surface proteins (MSPs), encoded by msp1 to msp5 genes of Anaplasma marginale, play an important role in host-pathogen and tick-pathogen interactions. These markers have been used for genetic characterization and phylogenetic studies. Despite domestic reports concerning suspected outbreaks of anaplasmosis in Thailand, genetic analysis of A. marginale in the country remains largely limited. Therefore, we aim to investigate the infection rate of the rickettsia organism in the Anaplasmataceae family throughout five regions of Thailand and to further characterize the key genetic markers: msp1a, msp2, and msp5 of A. marginale. From 2016 to 2021, we collected a total of 384 cattle blood samples across 18 provinces. Overall, the infection rate of the rickettsia organism in the Anaplasmataceae family was 46.1%. Over 65% of the positive samples were confirmed as A. marginale. We successfully obtained a total of 138 A. marginale msp1a (38), msp2 (79), and msp5 (21) sequences from all regions of the country. The msp1a and msp2 genes exhibit a high degree of genetic diversity, while the msp5 gene is highly conserved among the Thai isolates. Our findings regarding msp1a corroborated the genetic heterogeneity of A. marginale strains in endemic regions worldwide. Additionally, we found multiple novel variants for the first time in the current nationwide survey. We found 45 tandem repeat characters of the msp1a sequence. Among them, 24 characters were not shared with other countries. Collectively, we expanded the extent of genetic diversity in key markers; msp1a and msp2 genes, and further confirmed the previous finding that msp5 was highly conserved. The msp1a and msp2 genes could be useful for the surveillance of newly introduced strains. The current data may also be useful in designing a vaccine containing potential epitopes of different antigens in the future.

A newly optimized protocol to extract high-quality hemolymph from the cattle tick Rhipicephalus microplus: Improving the old conditions

Ticks are hematophagous ectoparasites with importance to animal and human health. In recent years, the study of ticks has had significant development, including immune response, vector-host interactions, physiological and multi-omics approaches. However, one of the main impediments is obtaining a significant amount of high-quality hemolymph. For this reason, we developed a protocol that allows obtaining up to 100 μl of hemolymph free of host blood per engorged tick. The technique consists of continuous hipocuticular punctures of the tick dorsum and an anticoagulant buffer that impedes hemolymph coagulation, allowing constant extravasation and ensuring high yields. Additionally, the hemocytes recovered with this protocol are intact and can be used for further analysis. The high-quality hemolymph obtained using this protocol and its applications will help to better understand the processes involving the hemolymph and its components. Although there are other hemolymph extraction protocols, the method developed here is very well suited for Rhipicephalus microplus, and in our experience, results in better yields and high-quality samples.