Anthelmintic activity and chemical profile of native plant extracts from the Yucatan Peninsula against Toxocara canis

Toxocara canis can produce the "larva migrans" syndrome in humans, and in puppies, it can cause severe digestive disorders. The most used treatments are based on anthelmintics, although there are reports of anthelmintic (AH) resistance. The Yucatan Peninsula has a great variety of plant species whose AH properties are still unknown. The objective of this study was to evaluate the in vitro AH activity of ethanolic (EE), methanolic (ME) and aqueous (AE) extracts from the leaves of five native plant species of the Yucatan Peninsula on T. canis eggs of dogs from Merida, Yucatan. As part of a screening, the EE of the plants Alseis yucatanensis, Calea jamaicensis, Cameraria latifolia, Macrocepis diademata, and Parathesis cubana were evaluated at doses of 2400 and 3600 μg/ml. The EE and AE of A. yucatanensis and M. diademata presented high percentages (≥ 91.3%) of inhibition of the larval development of T. canis after six days of exposure. The lowest LC50 and LC99 was presented by the ME from A. yucatanensis (255.5 and 629.06 µg/ml, respectively) and the ME from M. diademata (222.4 and 636.5 µg/ml, respectively), and the AE from A. yucatanenesis (LC50 of 535.9 µg/ml). Chemical profiling of the most potent AH extract (Alseis yucatanensis) was carried out by LC-UV-HRMS. Data from the ME and AE from this plant indicated the presence of the known glucosylngoumiensine, kaempferol 3,7-diglucosyde, uvaol, linoleic acid and linolenic acid together with unknown alkaloids. The EE, ME and AE from leaves of M. diademata and A. yucatanensis could be developed as natural alternatives to control T. canis.

First report of acaricidal efficacy from plumbagin on larvae of Rhipicephalus microplus and Rhipicephalus sanguineus resistant to conventional acaricides

The problem of resistance to acaricides in ticks such as Rhipicephalus microplus and R. sanguineus has motivated the search for control alternatives, such as the use of extracts and secondary metabolites from plants. Plumbagin is a natural product present in plants such as Plumbago zeylanica L., Diospyros kaki, and D. anisandra, of which acaricidal activity has been reported. Therefore, the objective of this study was to evaluate in vitro the acaricidal efficacy of plumbagin on larvae of R. microplus and R. sanguineus resistant to conventional acaricides. Larvae from engorged female ticks, collected from naturally infested dairy cattle and domiciled dogs, in Yucatan, Mexico, were used. The larval packet test and the larval immersion test were performed to detect acaricide susceptibility. Both tick populations were detected as resistant to cypermethrin and amitraz. Then, the modified larval immersion test was used and plumbagin was evaluated at concentrations of 1%, 0.5%, 0.25%, and 0.125% (%w/v), obtaining a mortality of 100% in the four concentrations for both tick species. Subsequently, lower doses of plumbagin were evaluated at concentrations of 0.0625%, 0.03125%, 0.015625% and 0.0078125%, obtaining mortalities of 100 to 36.26% for R. microplus and 100%-5.33% for R. sanguineus. Using Probit analysis, lethal concentrations at 50% (LC50), 99% (LC99) and confidence intervals at 95% (CI95%) were calculated. R. microplus showed a LC50 of 0.011% (CI95%: 0.010-0.011) and LC99 of 0.019% (CI95%: 0.018-0.022). R. sanguineus presented a LC50 of 0.017% (CI95%: 0.015-0.018) and CL99 of 0.031% (CI95%: 0.027-0.036). It was concluded that plumbagin has high acaricidal efficacy against larvae of R. microplus and R. sanguineus resistant to amitraz and cypermethrin. R. microplus larvae were significantly more susceptible to LC50 and LC99 compared to R. sanguineus. This is the first report on the acaricidal efficacy of plumbagin on larvae of R. microplus and R. sanguineus resistant to conventional acaricides.

Plant products and secondary metabolites with acaricide activity against ticks

The present review documents the results of studies evaluating the acaricidal activity of different plant products and secondary metabolites against ticks that are resistant and susceptible to conventional acaricides. Studies published from 1998 to 2016 were included. The acaricidal activity of plant extracts, essential oils and secondary compounds from plants have been evaluated using bioassays with ticks in the larval and adult stages. There is variable effectiveness according to the species of plant and the concentrations used, with observed mortalities ranging from 5 to 100% against the Rhipicephalus (Boophilus), Amblyomma, Dermacentor, Hyalomma, and Argas genera. A number of plants have been reported to cause high mortalities and/or affect the reproductive capacity of ticks in the adult phase. In the majority of these trials, the main species of plants evaluated correspond to the families Lamiaceae, Fabaceae, Asteraceae, Piperaceae, Verbenaceae, and Poaceae. Different secondary metabolites such as thymol, carvacrol, 1,8-cineol and n-hexanal, have been found to be primarily responsible for the acaricidal activity of different essential oils against different species of ticks, while nicotine, dibenzyldisulfide and dibenzyltrisulfide have been evaluated for plant extracts. Only thymol, carvacrol and 1,8-cineol have been evaluated for acaricidal activity under in vivo conditions. The information in the present review allows the conclusion that the secondary metabolites contained in plant products could be used as an alternative for the control of ticks that are susceptible or resistant to commercial acaricides.

Synergistic action of fatty acids, sulphides and stilbene against acaricide-resistant Rhipicephalus microplus ticks

Six compounds in a methanolic extract of Petiveria alliacea stem (cis-stilbene; benzyl disulphide; benzyl trisulphide; and methyl esters of hexadecanoic acid, octadecadienoic acid and octadecenoic acid) are known to exercise acaricide activity against cattle tick Rhipicephalus microplus larvae and adults. The synergistic effect of 57 combinations of these six compounds on acaricide activity against R. microplus was evaluated. Larvae immersion tests produced the lethal concentrations needed to kill 50% (LC₅₀) and 99% (LC₉₉) of the population. Adult immersion tests produced rates (%) for mortality, oviposition inhibition and eclosion inhibition. Individually, none of the compounds (1% concentration) exhibited acaricide activity (mortality ≤2.3%). When combined, however, nine mixtures exhibited a synergistic increase in activity, with high mortality rates (≥92%) in larvae. Values for LC₅₀ ranged from 0.07 to 0.51% and those for LC₉₉ from 0.66 to 5.16%. Thirty six compound mixtures had no significant activity (mortality ≤30%) against larvae. Two mixtures exhibited synergism against adults, with high rates (≥92%) of oviposition inhibition. The mixtures based on the benzyl disulphide+benzyl trisulphide pairing produced a synergistic effect against acaricide-resistant R. microplus larva and adults, and are therefore the most promising combination for controlling this ubiquitous ectoparasite.

Use of Ivermectin as Endoparasiticide in Tropical Cattle Herds Generates Resistance in Gastrointestinal Nematodes and the Tick Rhipicephalus microplus (Acari: Ixodidae)

The objective of the present study was to determine simultaneously the status of resistance against ivermectin (IVM) in gastrointestinal nematodes (GIN) and Rhipicephalus microplus (Canestrini, 1888) ticks in 12 cattle farms where IVM was used for the control of GIN in the Mexican tropics. Six farms had frequent use of IVM (≥ 4 times per year) and six farms had low frequency of IVM use (1-2 times per year). The fecal egg count reduction test and the larval immersion test were used to determine the resistant status of GIN and R. microplus against IVM, respectively. The results indicated that 100% of the surveyed farms had IVM-resistant GIN (reduction % from 0 to 67%). The genera involved were Haemonchus, Cooperia, Ostertagia, Trichostrongylus, and Oesophagostomum. Although the IVM was never used for the control of ticks, 50% of the surveyed farms presented GIN and R. microplus simultaneously resistant to IVM. Furthermore, two R. microplus populations showed high resistance ratio (RR) to IVM (farm TAT: RR50% = 7 and RR99% = 40.1; and farm SLS: RR50% = 2.4; RR99% = 11.0). A high frequency of IVM use (≥ 4 times per year) seemed to promote IVM resistance amongst R. microplus ticks compared with the farms with low frequency of IVM use (1-2 times per year; 66.6 vs. 25.0%, respectively). However, the number of surveyed farms was insufficient to show clear statistical inferences (odds ratio = 6.00; 95% CI = 0.341-105.5). The use of IVM for the control of GIN promoted simultaneously the development of IVM resistance in the GIN and R. microplus populations of the cattle herds surveyed.

Red deer (Cervus elaphus) as a host for the cattle tick Rhipicephalus microplus (Acari: Ixodidae) in Yucatan, Mexico

Rhipicephalus microplus is the most economically important cattle tick in the Mexican tropics. Wild ungulate species, including red deer (Cervus elaphus), are gaining popularity in diversified livestock ranching operations in Mexico. However, there is no information available on the susceptibility of red deer to infestation with the cattle tick, R. microplus, under hot, subhumid tropical conditions in Mexico. Biological data on R. microplus as an ectoparasite of cattle and red deer in a farm in the Mexican tropics are presented here. Ticks collected from red deer were identified as R. microplus (97 %) and Amblyomma cajennense (3 %), and tick species infesting cattle included R. microplus (95 %) and A. cajennense (5 %). Standard counts of R. microplus engorged females on red deer were 11 times higher than on cattle (428 ± 43 vs. 40 ± 18; p < 0.001). The reproductive efficiency index and larval hatching of R. microplus collected from cattle and red deer were similar (p > 0.05). Hemolymph samples of R. microplus collected from cattle were positive for Babesia spp. (10 %, 2/50) and all the samples from ticks infesting red deer were negative. Seventeen and ten percent of the blood samples from cattle and red deer were positive for Anaplasma marginale, respectively. The role of red deer as a host of R. microplus in Yucatan, Mexico and the importance of this host-parasite relationship relative to the epidemiology of R. microplus-borne diseases are discussed.

In vitro and in vivo evaluation of cypermethrin, amitraz, and piperonyl butoxide mixtures for the control of resistant Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) in the Mexican tropics

A study was conducted to evaluate the efficacy of cypermethrin, amitraz, and piperonyl butoxide (PBO) mixtures, through in vitro laboratory bioassays and in vivo on-animal efficacy trials, for the control of resistant Rhipicephalus (Boophilus) microplus on cattle in the Mexican tropics. Also, to examine mechanisms of resistance to cypermethrin in this tick population, the frequency of a mutated sodium channel gene (F1550I) was determined using a PCR assay. Results of laboratory bioassays using modified larval packet tests revealed that cypermethrin toxicity was synergized by PBO (from 46.6-57.0% to 83.7-85.0% larval mortality; P<0.05). The cypermethrin and amitraz mixture showed an additive effect (from 46.6-57.0% to 56.0-74.3% larval mortality). Strong synergism was observed with the mixture of cypermethrin+amitraz+PBO and this mixture was the most effective killing resistant tick larvae in vitro (96.7-100% of larval mortality). Tick larvae surviving exposure to cypermethrin or mixtures either with amitraz and PBO in vitro showed 2.9-49.6 higher probability to present the mutated allele than those killed by acaricide treatment (P<0.05). In the in vivo trial, the mixtures containing cypermethrin+PBO (80.6-97.3%), and cypermethrin+amitraz (87.0-89.7%) were more efficacious than cypermethrin alone (76.3-80.5%). The highest level of efficacy was obtained with the mixture of cypermethrin+amitraz+PBO, which yielded >95% control that persisted for 28 days post-treatment against R. microplus infesting cattle when tested under field conditions in the Mexican tropics. Although this mixture is a potentially useful tool to combat pyrethroid resistance, a product based on an acaricide mixture like the one tested in this study has to be used rationally.

Evolution of acaricide resistance: phenotypic and genotypic changes in field populations of Rhipicephalus (Boophilus) microplus in response to pyrethroid selection pressure

There have been few, if any, studies of arthropod field populations quantifying the kinetics of evolution of phenotypic and genotypic resistance to chemicals in response to the presence or absence of selection pressure. A prospective intervention study was undertaken over 2 years in Mexico to measure changes in resistance phenotype and genotype in the presence or absence of pyrethroid selection pressure on field populations of Rhipicephalus (Boophilus) microplus ticks on 11 farms with varying degrees of pyrethroid resistance. The resistance phenotype was evaluated by bioassay in a larval packet test expressed as the resistance factor (RF) derived from probit analysis of dose mortality regressions, and resistance genotype by an allele-specific PCR (AS-PCR) to determine the frequency of a sodium channel mutation (F1550I) associated with pyrethroid resistance. To validate the AS-PCR, a Pyrosequencing™ method was developed to detect the F1550I mutation. There was good concordance with the genotypes identified by both Pyrosequencing™ and AS-PCR (Kappa: 0.85). On five farms cypermethrin (CY) was exclusively used at intervals and on six farms amitraz was used. On two of the five CY-treated farms, the experiment was prematurely terminated due to unacceptably high levels of tick resistance. For all five farms, after 8-24 months of continued selection pressure with CY, the RF had increased 2-125-fold. The frequency of the resistance allele increased on all five farms from a starting range of 5-46% to a range of 66-95% after 8-24 months. On six farms treated with amitraz neither the RF nor the frequency of the resistance allele changed. A clear correlation between the phenotype and genotype was found in three of four treated farms confirming that the F1550I mutation is a major cause of synthetic pyrethroid resistance in Mexico. These results show that the pyrethroid resistance trait is stable (> 2 years) and that resistance is acquired much faster than it is lost. Hence, alternation of pyrethroid acaricide with other chemicals is likely to lead to the stepwise acquisition of synthetic pyrethroid resistance but not additional prolongation of its efficacious lifespan.

Survey of Rhipicephalus microplus resistance to ivermectin at cattle farms with history of macrocyclic lactones use in Yucatan, Mexico

Engorged females of Rhipicephalus microplus were collected from 30 cattle farms in Yucatan, Mexico to evaluate ivermectin resistance. The larval progeny of each tick sample were produced in laboratory and evaluated using the larval immersion test to obtain the larval mortality. Concentration-mortality data were subjected to probit analysis to generate lethal concentrations (LC). Resistance ratio (RR) of each tick sample was calculated by dividing its LC with that of an ivermectin-susceptible strain (Deutch). Field populations of R. microplus demonstrated various levels of resistance to ivermectin. The top three resistant populations were CHPAT (RR(50)=10.23, RR(99)=179.6), SDGO (RR(50)=7.37, RR(99)=115.3) and FND (RR(50)=7.09, RR(99)=50.22). The level of ivermectin resistance in most tick samples from cattle farms in Yucatan, Mexico were relatively low. However, the intensive use of macrocyclic lactones to control both endo- and ectoparasites in the region will likely lead to a more serious resistance problem that may cause control failure in the future.

Acaricidal activity of extracts from Petiveria alliacea (Phytolaccaceae) against the cattle tick, Rhipicephalus (Boophilus) microplus (Acari: ixodidae)

The acaricidal activity of crude extracts and fractions from stems and leaves of Petiveria alliacea (Phytolaccaceae) was carried out on larvae and adults of the cattle tick Rhipicephalus (Boophilus) microplus using the larval immersion test (LIT) and adult immersion test (AIT), respectively. Methanolic extracts of stems and leaves of P. alliacea showed 100% mortality on the LIT bioassay. On the other hand, methanolic extracts of leaves and stem on the AIT test showed 26% and 86% of mortality, respectively, egg laying inhibition of 40% and 91%, respectively and hatchability inhibition of 26% and 17%, respectively. Purification of the active stem methanolic extract showed that the activity was present in the n-hexane non-polar fraction. Bioassay-guided purification of the n-hexane fraction produced 10 semi-purified fractions; fraction B had the highest activity against tick larvae (100% mortality). Gas chromatography-mass spectrometry demonstrated that the chemical composition of the active fraction B samples were mainly composed of benzyltrisulfide (BTS) and benzyldisulfide (BDS). These metabolites might be responsible for the acaricidal activity of stem extract of P. alliacea. However, further experiments to evaluate the acaricidal activity of BTS and BDS on larvae and adults of R. (B.) microplus are needed. Our results showed that P. alliacea is a promising biocontrol candidate as acaricide against R. (B.) microplus resistant strains.

Factors affecting the prevalence of mange-mite infestations in stray dogs of Yucatán, Mexico

The aim of the present study was to determine the factors affecting the prevalence of mange-mite infestations in stray dogs of Yucatán, Mexico. The study was carried out in 200 stray dogs of Mérida capital city of Yucatán, Mexico. Four samples (head, thoracic-abdominal area, extremities and ear) were taken from each animal by skin scraping and examined microscopically in 10% KOH solution to detect the presence of mites. Mites were also collected from the external ear canal of dogs using cotton-tipped swabs. The prevalence of different mite species was calculated. A primary screening was performed using 2xK contingency tables of exposure variables. All variables with P< or =0.20 were analyzed by a logistic-binomial regression. The overall prevalence was 34%. Demodex canis (23.0%) was the most frequent mite, followed by Sarcoptes scabei var. canis (7.0%) and Otodectes cynotis (3.5%). The following factors were found: body condition (bad, OR: 5.35, CI 95%: 1.66-17.3; regular, OR: 3.72, CI 95%: 1.39-9.99) and the presence of macroscopic lesions of dermatosis (OR: 42.80, CI 95%: 13.65-134.24).