Advances in diagnosis of gastrointestinal nematodes in livestock and companion animals

Diagnosis of gastrointestinal nematodes in livestock and companion animals has been neglected for years and there has been an historical underinvestment in the development and improvement of diagnostic tools, undermining the undoubted utility of surveillance and control programmes. However, a new impetus by the scientific community and the quickening pace of technological innovations, are promoting a renaissance of interest in developing diagnostic capacity for nematode infections in veterinary parasitology. A cross-cutting priority for diagnostic tools is the development of pen-side tests and associated decision support tools that rapidly inform on the levels of infection and morbidity. This includes development of scalable, parasite detection using artificial intelligence for automated counting of parasitic elements and research towards establishing biomarkers using innovative molecular and proteomic methods. The aim of this review is to assess the state-of-the-art in the diagnosis of helminth infections in livestock and companion animals and presents the current advances of diagnostic methods for intestinal parasites harnessing (i) automated methods for copromicroscopy based on artificial intelligence, (ii) immunodiagnosis, and (iii) molecular- and proteome-based approaches. Regardless of the method used, multiple factors need to be considered before diagnostics test results can be interpreted in terms of control decisions. Guidelines on how to apply diagnostics and how to interpret test results in different animal species are increasingly requested and some were recently made available in veterinary parasitology for the different domestic species.

The Rhipicephalus appendiculatus tick vector of Theileria parva is absent from cape buffalo (Syncerus caffer) populations and associated ecosystems in northern Uganda

Rhipicephalus appendiculatus is the major tick vector of Theileria parva, an apicomplexan protozoan parasite that causes the most economically important and lethal disease of cattle in East and central Africa. The African cape buffalo (Syncerus caffer) is the major wildlife host of T. parva from southern Uganda and Kenya to southern Africa. We show herein that R. appendiculatus appears to be absent from the two largest national parks in northern Uganda. Syncerus caffer is common in both of these national parks, specifically Murchison falls (MFNP) and Kidepo Valley (KVNP). We re-confirmed the previously reported absence of T. parva in buffalo sampled in the two northern parks based on RLB data using a nested PCR based on the T. parva p104 gene. By contrast, T. parva-infected R. appendiculatus ticks and parasite-infected buffalo were present in Lake Mburo (LMNP) in South central Uganda. This suggests that the distribution of R. appendiculatus, which is predicted to include the higher rainfall regions of northern Uganda, may be limited by additional, as yet unknown factors.

P-glycoproteins play a role in ivermectin resistance in cyathostomins

Anthelmintic resistance is a global problem that threatens sustainable control of the equine gastrointestinal cyathostomins (Phylum Nematoda; Superfamily Strongyloidea). Of the three novel anthelmintic classes that have reached the veterinary market in the last decade, none are currently licenced in horses, hence current control regimens focus on prolonging the useful lifespan of licenced anthelmintics. This approach would be facilitated by knowledge of the resistance mechanisms to the most widely used anthelmintics, the macrocyclic lactones (ML). There are no data regarding resistance mechanisms to MLs in cyathostomins, although in other parasitic nematodes, the ABC transporters, P-glycoproteins (P-gps), have been implicated in playing an important role. Here, we tested the hypothesis that P-gps are, at least in part, responsible for reduced sensitivity to the ML ivermectin (IVM) in cyathostomins; first, by measuring transcript levels of pgp-9 in IVM resistant versus IVM sensitive third stage larvae (L3) pre-and post-IVM exposure in vitro. We then tested the effect of a range of P-gp inhibitors on the effect of IVM against the same populations of L3 using the in vitro larval development test (LDT) and larval migration inhibition test (LMIT). We demonstrated that, not only was pgp-9 transcription significantly increased in IVM resistant compared to IVM sensitive L3 after anthelmintic exposure (p < 0.001), but inhibition of P-gp activity significantly increased sensitivity of the larvae to IVM in vitro, an effect only observed in the IVM resistant larvae in the LMIT. These data strongly implicate a role for P-gps in IVM resistance in cyathostomins. Importantly, this raises the possibility that P-gp inhibitor-IVM combination treatments might be used in vivo to increase the effectiveness of IVM against cyathostomins in Equidae.

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Pgp-9 transcript levels were higher in ivermectin resistant versus susceptible cyathostomin populations.

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P-gp inhibitors increased ivermectin effect against cyathostomins in vitro.

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P-gp activity may play a role in ivermectin resistance in cyathostomins.

Deletion of LTbetaR augments male susceptibility to Plasmodium chabaudi

SUMMARY Disruption of the lymphotoxin beta receptor (LTbetaR) gene has been shown to result in enhanced resistance of female mice to blood-stage Plasmodium chabaudi malaria. Here, we investigate the effect of LTbetaR deletion on host defence of males. In contrast to females, male LTbetaR(-/-) mice do not exhibit any increase in resistance. Conversely, they are even more susceptible than wild-type C57BL/6 mice, which becomes evident after lowering circulating levels of testosterone by castration, which makes C57BL/6 males resistant, whereas LTbetaR(-/-) remain susceptible. Gene-expression analysis using cDNA arrays revealed no differences in immunological responses in spleen of malaria-resistant female and malaria-susceptible castrated male LTbetaR(-/-) mice. In the liver, however, expression levels of plasminogen activator inhibitor PAI1, chemokine CXCL10, dual specificity phosphatase DUSP1, and hydroxysteroid-specific sulfotransferases Sult2a1/2 were decreased 6- to 85-fold in susceptible castrated male LTbetaR(-/-) mice in comparison to resistant female LTbetaR(-/-) mice at maximal parasitaemia, as evidenced by Northern blot analyses. The present data support our previous view that the liver is involved in the combat against malarial blood stages and that down-regulation of the genes DUSP1 and Sult2a1/2 signals dysregulation of protective liver responses, thus possibly contributing to male susceptibility of LTbetaR(-/-) mice.

Rapid effects of androgens in macrophages

We investigated the existence of membrane receptors for testosterone (mAR) in mouse macrophages of the cell lines IC-21 and RAW 264.7 as well as their roles in nongenomic pathways, gene expression and cell functioning. Both cell lines lack intracellular androgen receptors (iARs) and respond to testosterone with rapid rises in [Ca2+]i. These rises in [Ca2+]i can neither be inhibited by iAR- nor by iER blockers, but are rather mediated through mAR. Pharmacological approaches suggest that the mAR belongs to the class of membrane receptors which are coupled to phospholipase C via pertussis toxin (PTX) sensitive G-proteins. The mAR can be localized as specific surface binding sites for testosterone-BSA-FITC by confocal laser scanning microscopy (CLSM)and flow cytometry, and are characterized by their agonist-sequestrability. In order to examine a possible role of the testosterone-induced rise in [Ca2+]i on gene expression, a c-fos promoter reporter gene construct was transfected into RAW 264.7 macrophages. The increase in [Ca2+]i induced by testosterone cannot significantly activate the c-fos promoter directly. Also, no significant activation of ERK1/2, JNK/SAPK and p38 can be observed following testosterone-stimulation alone. However, testosterone-induced rises in [Ca2+]i do have specific effects on gene expression in context with lipopolysaccharide (LPS)-induced genotropic signaling: testosterone specifically down-regulates LPS-induced activation of c-fos promoter, p38 MAPK and NO production. In fetal calf serum (FCS)-induced genotropic signaling, the situation is reversed, i.e. testosterone augments the activation of c-fos promoter and ERK1/2. Our studies demonstrate a cross-talk between the testosterone-induced nongenomic Ca2+ signaling and the genotropic signaling induced by LPS and FCS in macrophages.

Spleen-specific expression of the malaria-inducible intronless mouse gene imap38

We characterize the mouse gene imap38 and its inducibility by Plasmodium chabaudi malaria among different lymphoid tissues and mouse strains of different H-2 complex and non-H-2 background. Imap38 is a single copy gene assigned to chromosome 6B. It consists of only one exon of 1900 base pairs encoding a highly basic 25.8-kDa protein. Confocal laser scanning microscopy localizes differently tagged IMAP38 proteins in nuclei of transfected cells. Reporter gene assays reveal that the 1730-base pair 5'-flanking region, containing an RSINE1 repeat immediately adjacent to initiation site +1, exhibits promoter activity in nonmurine cells, while it is largely repressed in diverse mouse cell lines, which corresponds to the situation in mouse tissues. P. chabaudi malaria induces imap38 expression almost exclusively in the spleen but not in other lymphoid organs. Parasite lysates are able to induce imap38 in the spleen, but not in spleen cells ex vivo. Activation of spleen cells by LPS and other stimuli is not sufficient to induce imap38. Inducibility of imap38 requires signals from both parasites and the intact spleen, and it is controlled by genes of that non-H-2 background, which also controls development of protective immunity against P. chabaudi malaria.

Characterization of a hexokinase encoding cDNA of the parasitic nematode Hhaemonchus contortus

The nematode Haemonchus contortus is an important parasite of cattle and sheep. We describe here the cloning of a cDNA encoding a 53 kDa hexokinase (EC 2.7.1.1). The deduced protein shows 73% identity to a 50 kDa hexokinase deduced from a Caenorhabditis elegans cosmid. Alignment with mammalian hexokinases reveals two short amino acid insertions in the H. contortus hexokinase. Software tools for structural protein analysis (ExPASy server, Geneva) localize these insertions on the surface of the molecule, suggesting these surface changes as potential target sites for chemotherapeutic drugs.

Novel gene expressed in spleen cells mediating acquired testosterone-resistant immunity to Plasmodium chabaudi malaria

We report the identification of a novel mouse cDNA encoding IAP38, a putative plasma membrane protein of 38 kDa in splenic macrophages, B cells and T cells. The expression of iap38 is induced by blood-stage infections of Plasmodium chabaudi malaria and is testosterone-sensitive in non-immune mice. However, when mice have acquired testosterone-resistant immunity to P. chabaudi, there is an about 40-fold increase in the expression of iap38, which has then largely lost its responsiveness to infection and testosterone. The gene iap38 is suggested to be involved in imparting spleen cells the ability to mediate testosterone-resistant immunity to P. chabaudi malaria.