Breeding cattle and sheep for resistance to gastrointestinal nematodes

Gastrointestinal nematodes are an important cause of reduced production of meat, milk and wool in domestic livestock. It is generally believed that problems caused by these parasites have increased owing to the intensification of animal husbandry(1-3) of resistance to anthelmintics, current research is focussed on alternative control strategies that do not rely on anthelmintics. Here, Bram Kloosterman, Henk Parmentier and Harm Ploeger review work on the genetic resistance of domestic ruminants to these nematodes and discuss the practicality of breeding programmes.     

Skin test to detect resistance of cattle to Rhipicephalus appendiculatus ticks

The evaluation of a skin test to detect acquired resistance to Rhipicephalus appendiculatus Neumann ticks is described. An extract of salivary glands of partially fed female R. appendiculatus was prepared by dissection, sonication and filtration and used for intra-dermal injection. Tests were carried out on twelve calves of known resistance to R. appendiculatus and on twelve naive calves to establish threshold values for positive reactions. Four rabbits naive to ticks were skin tested repeatedly to assess immunogenicity of the test. Reactions to the test at 1 h and at 24 h after injection were significantly correlated with resistance. The correlation was higher with the reactions at 24 h. Rabbits were immunized by the test but the reactions never exceeded the positive threshold. Further development by field testing is recommended.     

An assessment of host resistance to ticks on cross-bred cattle in Burundi

Abstract. Groups of cattle of four different cross-breeds (Ankole × Friesian, Ankole × Brown-Swiss, Ankole × Guernsey, Ankole × Sahiwal) plus a group of pure Ankole cattle were immunized against tick-borne diseases: East Coast Fever, using a Theileria parva trivalent vaccine, and anaplasmosis, babesiosis and, subsequently, heartwater. With the exception of two small subgroups of Ankole and Ankole × Sahiwal which were treated by weekly spraying using Delnav, all the groups were exposed to natural field challenge of ticks to quantify the development of host resistance to ticks. The results indicate resistance to the most abundant species, Rhipicephalus appendiculatus , as follows: Ankole > Ankole × Sahiwal > Ankole × Brown Swiss > Ankole × Friesian > Ankole × Guernsey. In both Amblyomma variegatum and Rhipicephalus evertsi evertsi , the manifestation of different levels of resistance between breeds is inapparent. Correlations between total ticks and standard female ticks were good for R. appendiculatus (r = 0.73) and R. evertsi (r - 0.51) but poor for A. variegatum (r = 0.31). Correlations between species were reasonably consistent (r = 0.43-0.59). There was no significant correlation between tick burdens and daily liveweight gain (DLWG) over the. whole period of the study. Of the cross-bred groups, Ankole × Sahiwal, which had the highest level of resistance, had the highest DLWG. In contrast, the Ankole × Guernsey which developed the lowest level of resistance had only marginally lower DLWG, the difference being only 8 g/day. During the first period of exposure to ticks, however, the untreated Ankole × Sahiwal group had markedly lower DLWG, which may indicate that the development and manifestation of resistance is at the expense of productivity.     

Comparison of resistance in three breeds of cattle against African ixodid ticks

Tick resistance in three breeds of cattle, two indigenous breeds (Arssi and Boran) and one Boran x Friesian cross-breed, were compared following natural tick infestations at Abernossa ranch in Ethiopia. The local Arssi breed was found to have the highest tick resistance, followed by the Boran breed, whereas the Boran x Friesian was the least resistant. Over a period of 12 months, from October 1991 to September 1992, a total of 32 897 ticks composed of four genera were collected from the animals. The four most abundant tick species were Amblyomma variegatum (61.7%), Boophilus decoloratus (16%); Rhipicephalus evertsi evertsi (16.3%) and Hyalomma marginatum rufipes (3.7%). Furthermore, 63.5% of all ticks were collected from cross-breed cattle, and 26.2% from the Boran, whereas the local Arssi breed carried only 10.3%. The results indicated that cattle resistant to one species of tick were also resistant to other tick species.     

Analysis of putative inhibitors of anthelmintic resistance mechanisms in cattle gastrointestinal nematodes

Effects of the cytochrome P450 inhibitor piperonyl butoxide and the P-glycoprotein inhibitor verapamil on the efficacy of ivermectin and thiabendazole were studied in vitro in susceptible and resistant isolates of the cattle parasitic nematodes Cooperia oncophora and Ostertagia ostertagi. The effects of combined use of drug and piperonyl butoxide/verapamil, respectively, were investigated in the Egg Hatch Assay, the Larval Development Assay and the Larval Migration Inhibition Assay. The effects of piperonyl butoxide and verapamil as inhibitors of thiabendazole and ivermectin responses were particularly marked for larval development, where both inhibitors were able to completely eliminate all differences between susceptible and resistant isolates. Even the lowest concentrations of anthelmintics used in combination with inhibitors caused complete inhibition of development. Differences and/or similarities among responses in different isolates were only obtained in the two other assays: in the Egg Hatch Assay piperonyl butoxide caused a shift in concentration–response curves obtained with thiabendazole to the left for all isolates tested, changing relative differences between isolates. In contrast, an effect of verapamil in the Egg Hatch Assay was only apparent for benzimidazole-resistant isolates. In the Larval Migration Inhibition Assay only ivermectin was tested and piperonyl butoxide shifted the concentration–response curves for all isolates to the left, again eliminating differences in EC₅₀ values between susceptible and resistant isolates. This was not the case using verapamil as an inhibitor, where curves for both susceptible and benzimidazole-resistant isolates shifted to the left in Ostertagia isolates. In Cooperia the picture was more complex with ivermectin-resistant isolates showing a larger shift than the susceptible isolate. Single nucleotide polymorphisms in the β-tubulin isotype 1 gene were investigated. Significantly increased frequencies of resistance-associated alleles were observed for the codons 167 and 200 in one benzimidazole-resistant isolate but not in an isolate selected for benzimidazole resistance at an early stage of selection.     

Entomopathogenic nematodes for the biocontrol of ticks.

Entomopathogenic steinemematid and heterorhabditid nematodes are increasingly used to control insect pests of economically important crops. Laboratory and field simulation trials show that ticks are also susceptible to these nematodes. The authors review the potential of entomogenous nematodes for the control of ticks.     

Fat: Love it to death!

Comment on: Rockenfeller P, et al. Cell Cycle 2010; 9:2836-42.     

A genome-wide survey reveals a deletion polymorphism associated with resistance to gastrointestinal nematodes in Angus cattle

Gastrointestinal (GI) nematode infections are a worldwide threat to human health and animal production. In this study, we performed a genome-wide association study between copy number variations (CNVs) and resistance to GI nematodes in an Angus cattle population. Using a linear regression analysis, we identified one deletion CNV which reaches genome-wide significance after Bonferroni correction. With multiple mapped human olfactory receptor genes but no annotated bovine genes in the region, this significantly associated CNV displays high population frequencies (58.26 %) with a length of 104.8 kb on chr7. We further investigated the linkage disequilibrium (LD) relationships between this CNV and its nearby single nucleotide polymorphisms (SNPs) and genes. The underlining haplotype blocks contain immune-related genes such as ZNF496 and NLRP3. As this CNV co-segregates with linked SNPs and associated genes, we suspect that it could contribute to the detected variations in gene expression and thus differences in host parasite resistance.     

Antimicrobial drug resistance in Staphylococcus aureus isolated from cattle in Brazil

Isolates of Staphylococcus aureus obtained from apparently healthy cattle in the State of Paraiba, Brazil were characterized in relation to resistance to 21 antimicrobial agents. Among the 46 isolates obtained, resistance to penicillin was most frequent, followed by resistance to cadmium, streptomycin, arsenate, tetracycline, mercury, erythromycin and kanamycin/neomycin. All isolates were susceptible to fusidic acid, ethidium bromide, cetrimide, chloramphenicol, benzalkonium chloride, doxycycline, gentamicin, methicillin, mnocycline, novobiocin, rifamycin, tylosin and vancomycin. Only six isolates were susceptible to all the drugs tested. With respect to the antibiotics, multi-resistant isolates were uncommon. These results are probably a consequence of the peculiarities of local drug usage pressures. In relation to metal ions, resistance to mercury was rare while resistance to arsenate was relatively frequent, which contrasts with the situation for human Staph. aureus strains. After treatment with ethidium bromide, elimination of resistance to penicillin, tetracycline, streptomycin, erythromycin and cadmium was observed, which was consistent with the genetic determinants being plasmid-borne.     

Mortality rate of adult ticks due to infection by entomopathogenic nematodes

The mortality of Boophilus annulatus, Hyalomma excavatum, Rhipicephalus bursa, and Rhipicephalus sanguineus adult ticks was recorded after their exposure in petri dishes to 5 entomopathogenic nematode strains. The strains used were DT and Mexican of Steinernema carpocapsae, Hb HP88 of Heterorhabditis bacteriophora, and IS-3 and IS-5 of Heterorhabditis sp. The most rapid killing rates (LT50 and LT90) were observed for B. annulatus ticks (0.8-5.0 days). Most unfed males died 0.3-2.8 days after the unfed females, whereas even more time (0.8-8.0 days) passed before engorged females died. In most bioassays, the IS-3 and IS-5 strains of Heterorhabditis sp. nematodes appear to be the most pathogenic for ticks and, in most cases, killed ticks several days before the other 3 nematode strains. Unfed adult ticks exposed to nematodes died within less time than it takes for adults to complete their prefeeding period after molting.     

Factors affecting the virulence of entomopathogenic nematodes to engorged female Boophilus annulatus ticks

The laboratory trials rank the virulence of entomopathogenic nematode strains (3 heterorhabditids and 6 steinernematids) to engorged female Boophilus annulatus ticks according to 3 parameters of the infection process: the effect of exposure time on tick mortality, the quantity of nematodes that penetrate ticks, and the rate of tick mortality after the injection of 1, 2, or 3 nematodes. Exposure of the ticks to heterorhabditid strains for 6 hr resulted in >80% mortality, but only 20 or 65% mortality after exposure to most steinernematids. The quantity of nematodes recovered per tick exposed to nematodes for 6 days averaged from 16 to 141. For steinernematids, a negative correlation was obtained between tick mortality and the average quantity of nematodes recovered. Injecting 1 infective juvenile from 1 of 2 heterorhabditid strains into each tick resulted in close to 100% mortality. Increasing the quantity of nematodes injected into each tick had little or no additive effect on tick mortality.     

Effect of chemoprophylaxis on immunity to gastrointestinal nematodes in cattle

Control of gastrointestinal nematodes in first-season grazing cattle is largely based on either strategic anthelmintic treatment or use of anthelmintic-release devices. Control is evolving towards more efficacious anthelmintics and delivery systems, almost annihilating parasite contact. Here, Jozef Vercruysse, Hans Hilderson and Edwin Claerebout focus on the inverse relationship between the intensive use of modern anthelmintics and the build-up of immunity to gastrointestinal nematodes.     

Genomic regions showing copy number variations associate with resistance or susceptibility to gastrointestinal nematodes in Angus cattle

Genomic structural variation is an important and abundant source of genetic and phenotypic variation. We previously reported an initial analysis of copy number variations (CNVs) in Angus cattle selected for resistance or susceptibility to gastrointestinal nematodes. In this study, we performed a large-scale analysis of CNVs using SNP genotyping data from 472 animals of the same population. We detected 811 candidate CNV regions, which represent 141.8 Mb (~4.7%) of the genome. To investigate the functional impacts of CNVs, we created 2 groups of 100 individual animals with extremely low or high estimated breeding values of eggs per gram of feces and referred to these groups as parasite resistant (PR) or parasite susceptible (PS), respectively. We identified 297 (~51 Mb) and 282 (~48 Mb) CNV regions from PR and PS groups, respectively. Approximately 60% of the CNV regions were specific to the PS group or PR group of animals. Selected PR- or PS-specific CNVs were further experimentally validated by quantitative PCR. A total of 297 PR CNV regions overlapped with 437 Ensembl genes enriched in immunity and defense, like WC1 gene which uniquely expresses on gamma/delta T cells in cattle. Network analyses indicated that the PR-specific genes were predominantly involved in gastrointestinal disease, immunological disease, inflammatory response, cell-to-cell signaling and interaction, lymphoid tissue development, and cell death. By contrast, the 282 PS CNV regions contained 473 Ensembl genes which are overrepresented in environmental interactions. Network analyses indicated that the PS-specific genes were particularly enriched for inflammatory response, immune cell trafficking, metabolic disease, cell cycle, and cellular organization and movement.     

Evaluation of the Egg Hatch Assay and the Larval Migration Inhibition Assay to detect anthelmintic resistance in cattle parasitic nematodes on farms

Resistance to anthelmintic drugs, particularly to the widely used benzimidazoles (BZs) and macrocyclic lactones (MLs) is an increasing problem in cattle industries worldwide. Reliable methods for the assessment of anthelmintic efficacy in the field are required in order to react before resistance becomes an obvious problem on individual properties. The ability of the Egg Hatch Assay (EHA) and the Larval Migration Inhibition Assay (LMIA) to detect anthelmintic resistance under field conditions was evaluated on cattle farms in Northern Germany. As published previously Faecal Egg Count Reduction Test (FECRT) was performed using oral albendazole (Valbazen®) or injectable ivermectin (Ivomec®). Herein the FECRT results described earlier were compared with data from EHAs or LMIAs, respectively, performed with eggs from fresh faeces or larvae from faecal cultures of the tested animals before and after treatment. The obtained EC₅₀ values allowed the assessment of efficacy of albendazole and ivermectin on farm level. The results of the FECRTs and the results of both in vitro assays were comparable. In comparison to the FECRT the in vitro assays are less time, labour and cost intensive and are able to assess the susceptibility status of a worm population without treatment. Therefore both are beneficial alternatives for the reliable detection of reduced efficacy of these two drug classes on farms.     

Area-wide impact of macrocyclic lactone parasiticides in cattle dung

Following the treatment of cattle with veterinary parasiticides and insecticides, residues are excreted into the dung in concentrations that may be toxic to functionally important dung-colonizing insects. In the dung, these residues cause a range of well-studied lethal and sub-lethal effects, the magnitudes of which vary with the compound used, mode of administration and concentration, and the insect species in question. Particular concern has been associated with the use of macrocyclic lactones in this context. Loss of insect colonizers may delay pat decomposition, but field studies report contrasting results that reflect confounding factors such as weather conditions, pat moisture content, pat location, time of year and dung insect species phenologies. The question of fundamental concern is whether the impacts seen in experimental or laboratory studies are likely to have a functional impact on insect populations, community interactions and the economically important process of dung decomposition. Recent studies which have attempted to address these wider, landscape-level impacts in temperate ecosystems are reviewed here. These show that the extent to which chemical residues may have any sustained ecological impact will depend on both a range of farm management factors, such as the temporal and spatial patterns of chemical use, the number of animals treated and the choice of active ingredient, and a range of insect-related factors, such as abundance, population dynamics and dispersal rates. However, they also demonstrate that considerable uncertainty remains about the likely extent of such effects and that current data are insufficient to support firm conclusions regarding sustained pasture-level effects. More large-scale, longterm field experiments are required, particularly in relation to insect dispersal and functional interactions within the dung insect community.