Equine babesiasis: Epidemiology, control and chemotherapy

Equine piroplasmosis (EP) is a hemoprotozoan disease cased by Babesia caballi and B.equi. It is a tick-borne disease principally characterized by fever, anemia, and icterus. Clinically inapparent babesia carrier horses are important in the dissemination of the disease. Clinical episodes occur under two conditions:

1. When susceptible horse stock is moved into endemic EP areas; and

2. When inapparent babesia carriers are moved into non-endemic areas, then in the presence of certain ticks, babesiasis is spread to the susceptible horse population.

Ticks are the principal vectors of equine piroplasmosis, additionally contaminated hypodermic needles have shown to spread B. equi among horses. In endemic EP areas, it has been shown that babesiasis can cause unthriftyness in foals.Control of babesiasis is principally directed at tick control. Various tickacidal sprays or dips can be used to break the life cycle of ticks.Chemotherapy, using certain aromatic diamidines, is an adjunct to tick control and also facilitates the international relocation of horses and other equidae. Objectives of chemotherapy are divided as follows: 1. In EP endemic areas, the therapeutic aim is to subdue the babesia parasites and leave the host horse in a state of premunition; and 2. In non-endemic areas, complete clearance of babesia organisms from the animal is the objective. Several aromatic diamadine pharmaceuticals are available to veterinarians.During recent years, horses and other equidae have become important in international commerce. Such commerce has focused attention on the international spread of certain infectious and communicable animal disease; among these is equine piroplasmosis (EP).Piroplasmosis is an infectious hemoprotozoan disease characterized by fever, anemia, icterus, and other signs arising from hemolysis caused by Babesia caballi or Babesia equi. The disease has been reported in horses, mules, donkeys, and zebras.⁸     

Equine tapeworm infections: Disease,diagnosis and control

Equine tapeworm infection has gained increasing attention over the past few decades and a number of research studies have already been published. These focus primarily on the most common of the 3 tapeworm species, Anoplocephala perfoliata, although some new information has also been generated for the other two species, Anoplocephala magna and Anoplocephaloides mamillana. The preponderance of research studies have focused on development and validation of diagnostic techniques for tapeworm detection and the role of these parasites in equine gastrointestinal disease. Several diagnostic techniques have been found useful for diagnosis of A. perfoliata but each has its strengths and weaknesses. Egg counting techniques have been modified to achieve acceptable to good diagnostic performance but the trade‐off is often a more time‐consuming method. Validation studies indicate that these methods can reliably detect tapeworm burdens above 10 worms. Several enzyme‐linked immunosorbent assays (ELISAs) have been developed and made commercially available. These can generate useful information about tapeworm exposure on the herd level but are less reliable for individual diagnosis. Unfortunately, none of the available diagnostic techniques are useful for evaluating anthelmintic treatment efficacy. Coproantigen testing may find use as a future diagnostic modality but further characterisation is required. The large body of scientific evidence supports an association between A. perfoliata infection and certain types of equine colic, although some discrepancy exists between studies. Tapeworm surveillance and control should be considered as part of the overall parasite control strategy. When properly used, the currently available diagnostic tools can guide the veterinarian to make strategic decisions regarding tapeworm control.     

Common helminth infections of donkeys and their control in temperate regions

Roundworms and flatworms that affect donkeys can cause disease. All common helminth parasites that affect horses also infect donkeys, so animals that co‐graze can act as a source of infection for either species. Of the gastrointestinal nematodes, those belonging to the cyathostomin (small strongyle) group are the most problematic in UK donkeys. Most grazing animals are exposed to these parasites and some animals will be infected all of their lives. Control is threatened by anthelmintic resistance: resistance to all 3 available anthelmintic classes has now been recorded in UK donkeys. The lungworm, Dictyocaulus arnfieldi, is also problematical, particularly when donkeys co‐graze with horses. Mature horses are not permissive hosts to the full life cycle of this parasite, but develop clinical signs on infection. In contrast, donkeys are permissive hosts without displaying overt clinical signs and act as a source of infection to co‐grazing horses. Donkeys are also susceptible to the fluke, Fasciola hepatica. This flatworm can be transmitted, via snails and the environment, from ruminants. As with cyathostomins, anthelmintic resistance is increasing in fluke populations in the UK. A number of the anthelmintic products available for horses do not have a licence for use in donkeys, and this complicates the design of parasite control programmes. As no new equine anthelmintic classes appear to be near market, it is important that the efficacy of currently effective drugs is maintained. It is important that strategies are used that attempt to preserve anthelmintic efficacy. These strategies should be based on the concept that the proportion of worms in a population not exposed to anthelmintic at each treatment act as a source of ‘refugia’. The latter is an important factor in the rate at which resistance develops. Thus, it is imperative that parasite control programmes take into account the need to balance therapy to control helminth‐associated disease with the requirement to preserve anthelmintic effectiveness.     

Equine influenza virus infections: an update

Equine influenza is one of the most economically important contagious respiratory diseases of horses. In this paper the current state of knowledge of equine influenza virus and the most important aspects of these virus infections, e.g. epidemiology, clinical aspects, pathogenesis and pathology, immunity, diagnosis, treatment, management and vaccination, are reviewed with an emphasis on epidemiology, diagnosis and vaccinology. Many questions have remained and with the advent of improved technology new questions have arisen. Consequently, research priorities should be set in an attempt to answer them. Therefore, this review ends with some personal recommendations for important priorities for future research.     

Equine herpesvirus 1 and 4 infections: an update

Equine herpesvirus 1 (EHV1) and equine herpesvirus 4 (EHV4) are important ubiquitous equine viral pathogens, causing much damage to the horse industry. EHV1 strains are associated with respiratory disease, abortion, and paresis/paralysis, whereas EHV4 strains are predominantly associated with respiratory disease. In the past decades much research effort has been put into improving knowledge about these viruses. In this paper the current state of knowledge of these viruses and the most important aspects of these virus infections, e.g. epidemiology, clinical aspects, pathogenesis and pathology, immunity, diagnosis, preventive management and management in the course of an outbreak and vaccination, is reviewed. Because we performed some research ourselves in the areas of diagnosis, epidemiology and vaccinology these aspects are reviewed in more depth than the other aspects. Still many questions have remained and new questions have risen. Consequently, research priorities should be made in an attempt to answer these questions. Therefore, this review ends with some personal recommendations for important priorities for future research.     

Prevalence of helminth infections in swine in Denmark

During 1982-1984 the occurrence of helminths in 66 sow herds was determined by examining faecal samples from swine of different age groups. Ascaris suum was found in 88% of the herds, while Oesophagostomum spp. and Trichuris suis were found in 58 and 23% of the herds, respectively. Strongyloides ransomi and Hyostrongylus rubidus was not identified in any of the herds. The occurrence of both A. suum and Oesophagostomum spp. was strongly related to the age of the animals. A. suum was most frequently found in growing pigs (30% of the fatteners and 25% of the gilts), whereas only 11-19% of the animals of the adult stock were excreting eggs. In contrast the prevalence of Oesophagostomum spp. increased with the age of the hosts, from 10% of the fatteners to 35 and 44% of the sows and boars, respectively. T. suis occurred only very sporadically, with the highest prevalence being 3% in the gilts. In comparison to previous Danish surveys the present mean prevalences of A. suum and Oesophagostomum spp. were low. Extremely low herd prevalences were found among large herds with intensive management and housing. In these herds, the pigs were infected at a later stage in life than pigs in more traditionally managed herds.     

Treatment vs non-treatment of helminth infections in cattle: defining the threshold

Helminth infections are an important cause of lost productivity in livestock world-wide, often necessitating anthelmintic treatment. However, a large part of the anthelmintics are used indiscriminately because the parasite levels are too low to justify treatment or because the treatments are not correctly programmed, resulting in undertreatment or overtreatment. The objective of this paper is to discuss possible thresholds for anthelmintic treatment of some of the more important helminth infections in livestock, i.e. gastrointestinal nematodes, lungworms and liver fluke, to promote a more appropriate use of anthelmintics. When possible, a distinction is made between therapeutic thresholds, production-based thresholds and preventive thresholds. A "therapeutic threshold" is intended to identify (an) animal(s) with parasite levels that necessitate immediate treatment. The therapeutic threshold is basically the diagnosis of clinical disease, and can be determined relatively easily for the parasites discussed in this paper. A "production-based threshold" is intended to measure the effects of sub-clinical parasitism on productivity parameters, such as weight gain and milk yield, before clinical disease occurs. Finally, a "preventive threshold" is meant to predict future infection levels, to enable the application of appropriate control measures.     

Survey of helminth infections in Maine dairy cattle.

The survey was done to determine the incidence and seasonal prevalence of the gastrointestinal helminths infecting Maine dairy cattle. Approximately equal groups of calves, heifers, and cows from 13 dairy farms, managerially and geographically representative of dairying in the state, were sampled at regular 2-month intervals over the period of a year. On the basis of fecal egg counts and identification of cultured larvae, the following results were obtained: Of the 94 adult cows, 78 heifers, and 91 calves sampled continuously in the course of the survey, 95.7%, 98.7%, and 96.7%, respectively, were strongylorid positive (infected with Ostertagia, Cooperia, Trichostrongylus, Haemonchus, and Oesophagostomun), with an overall incidence of 97%. Strongyloides papillosus eggs were in 64.6% of the cattle, Bunostomum in 40.3%, Nematodirus in 27.8%, Trichuris in 27.0%, Capillaria in 9.5%, Moniezia in 25.1%, and Dictyocaulus viviparus larvae in 2.7%. Worm burdens, as reflected by mean nematode egg production per gram of feces, varied. The greatest worm burdens were in the calves, followed by the heifers and the cows. A marked variation in egg production related to season was observed, particularly with the strongylorid worms. Peak strongylorid egg production was observed in the May-June sampling period. After the peak period, worm burdens decreased in all groups of cattle to their lowest point during the winter period of January-February. This pattern of egg production was similar to that reported by workers in other parts of the world. Farm management practices were shown to be related to the degree of parasitism existing in these herds. Those herds classed as poorly managed had significantly higher levels of parasitism in young animals than those classed as having fair or good management.     

Recent advances in laboratory models for evaluation of helminth chemotherapy

Extensive research on nematodes of veterinary importance has resulted in new tests based on incubation of parasitic nematodes in culture media, with a variety of detection systems including visual observation, inhibition of aggregation, reduced secretion of acetylcholinesterase and electronic motility measurements. There has been a proliferation of tests to detect benzimidazole resistant nematodes including egg embryonation, egg hatch, larval motility, differences in esterases, and tubulin binding by labelled benzimidazoles. A simple larval development test, which detects resistance to all types of anthelmintics, is likely to become the preferred test for evaluation of resistance in nematodes of grazing animals. By contrast the relative unimportance of trematodes and cestodes from a commercial point of view has resulted in few recent developments in models for evaluating chemotherapy. But the emergence of drug resistant strains of both schistosomes and liver fluke indicates the need for simple tests to detect resistance.     

The prevalence of gastrointestinal helminth infections in pigs in Kenya

The prevalence of helminth infection, species spectrum and worm burdens in Kenyan pigs was examined. A total of 115 gastrointestinal tracts (GIT) from 61 growers and 54 adult pigs were examined between February 2005 and January 2006. Seventy eight (67.8%) had one or more helminth parasites, of which thirty six (31.3%) were mixed infection. Ten types of helminth parasites encountered in descending order of prevalence were, Oesophagostomum dentatum (39.1%), Trichuris suis (32.2%), Ascaris suum (28.7%), Oesophagostomum quadrispinulatum (14.8%), Trichostrongylus colubriformis (10.4%), Trichostrongylus axei (4.3%), Strongyloides ransomi (4.3%), Hyostrongylus rubidus (1.7%), Ascarops strongylina (1.7%) and Physocephalus sexalutus (0.9%). Oesophagostomum dentatum was the most prevalent species (51.9%) in the adult pigs, while Trichuris suis was the most prevalent species (44.3%) in growers. The highest worm counts were recorded in the out door production system. Oesophagostomum quadrispinulatum, Trichostrongylus colubriformis, Trichostrongylus axei, Hyostrongylus rubidus, Ascarops strongylina and Physocephalus sexalutus were recorded in Kenya for the first time. The high prevalence and wide spectrum observed in the present study suggests that helminth infection may be a constraint to economic pig production in the country and there is need to institute control measures.     

Epidemiological observations on helminth infections of calves in southern Ghana

Summary This paper describes helminth infections in three groups of calves of different ages grazing naturally infested pastures from March 1987 to May 1988. Calves in which the faecal egg output was followed from birth showedToxocara vitulorum eggs as early as two days after birth and maximum patency occurred after two months. The fall inToxocara egg output coincided with a rise in that of the strongylates;Haemonchus spp.,Trichostrongylus spp. andOesophagostumum spp. The influence of rainfall in dictating strongylate nematode infection was clear with high egg output during high rainfall and low egg counts when the rainfall was lower. There was an indication that calves carry the infection from the end of the minor rainy season in November to the beginning of the next rains in March and then contribute to pasture contamination. However, calves born in December may remain uninfected until the onset of the rains.

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Resumen Este trabajo discute infecciones helmínticas en tres grupos de terneras de edades diferentes, las cuales patoreaban pasturas infectadas, de marzo 1987 a mayo 1988. El grupo 3 en el cual el conteo de huevos por gramo de heces se siguió desde el nacimiento, presentó huevos deToxocara vitulorum desde los tres días, occuriendo la prepatencia máxima a los dos meses de edad. La caída de los huevos deToxocara coincidió con el aumento de los de estrongiloides;Haemonchus spp,Trichostrongylus spp andOesophagostomum spp. Se demuestra la influencia de la precipitación pluvial en la presencia de estrongilus, con una mayor cantidad de huevos por gramo de heces durante los meses de alta precipitación y de menor cantidad de huevos coincidiendo con una precipitación menor en ambos grupos, 2 y 3. Hubo indicación de que los becerros pueden transportar la infección desde el final de la estación lluviosa menor en noviembre hasta el comienzo de la siguiente estación lluviosa en marzo lo cual contribuye a la contaminación de las pasturas. Sin embargo, los becerros nacidos en diciembre, podrían conservarse sin contaminación severa hasta el principio de las lluvias.

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Résumé Cet article décrit les infestations à helminthes de 3 groupes de veaux d'ages différents paturant sur des prés naturellement infectés, entre mars 1987 et mai 1988. Le groupe 3, dans lequel le niveau des oeufs dans les fèces a été suivi depuis la naissance, a présenté des oeufs deToxocara vitulorum dès le deuxième jour, la mise en évidence maximale intervenant après 2 mois. La chute dans l'émission des oeufs deToxocara a co?ncidé avec l'élévation de ceux des strongyles tels queHaemonchus spp,Trichostrongylus spp etOesophagostomum spp. L'influence de la pluviométrie comme facteur déterminant de l'infection par les strongyles a été démontrée par la corrélation entre le niveau élevé des comptages d'oeufs pendant les fortes précipitations et leur bas niveau lors des faibles pluviosités, dans les groupes 2 et 3. On a noté que les veaux peuvent héberger l'infestation depuis la fin de la petite saison des pluies (en novembre) jusqu'au commencement des pluies suivantes en mars, ce qui peut contribuer à la contamination des paturages. Cependant des veaux nés en décembre peuvent rester indemnes jusqu'au début des pluies.

     

Equine parasite control using pyrantel embonate

Over a period of several years the use of pyrantel embonate in the control of helminth infections on three equine establishments was monitored by the examination of faecal samples collected immediately before each anthelmintic treatment. With a monthly interval between treatments for three years the faecal egg output of the horses remained at a very low level. One one establishment this was maintained when the treatment interval was extended to one-and-a-half months after treating monthly for two years. If a treatment interval of one-and-a-half months was used continuously for a number of years there was a cumulative effect, and the benefits, in terms of reduced faecal egg output of the horses, were more apparent during the second year of the control programme.     

Antigenic structure of nematodes and prospects for vaccination against helminth infections

Domestic animals may become resistant to parasites. There have been many studies of the nature and role of the antigens involved in this immunological reaction and the results are presented in this paper.The antigens may be the tissues of the worm itself (somatic antigens) or its secretions (metabolic antigens). Resistance to attack by parasites may be induced by using either live worms (very small numbers of parasites or irradiated larvae) or homogenised whole worms or extracts of their secretions. In favourable cases the administration of antigens may vaccinate the animal but it may also produce a state of tolerance.A precise knowledge and mastery of these factors should lead to the successful vaccination of animals against their parasites.

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Kurzfassung Bei Parasitentragern entwickelt sich häufig ein Resistenzzustand; Natur und Rolle der Antigene, die bei Immunitätsreaktionen beteiligt sind, haben viele Untersuchungen angeregt, deren Ergebnisse hier dargestellt werden. Die Antigene werden entweder durch die Gewebe des Fadenwurmes selbst (somatische Antigene) oder durch seine Ausscheidungen (metabolische Antigene) repräsentiert. Resistenz (Verseuchung mit einer ganz kleinen Menge von Parasiten oder mit bestrahlten Larven), mit ganzen zermalmten Würmern, oder mit Extrakten ihrer Ausscheidungen erreicht werden. Die Verabreichung von Antigenen Kann in günstigen Fällen zu einer Vakzination oder zu einem Tolleranzzustand führen. Genaue Kenntnisse und die Beherrschung dieser Faktoren sollten zu einer Vakzination der Tiere gegen ihre Parasiten führen.

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Resume Un état de résistance se développe chez les animaux porteurs de parasites; la nature et le rôle des antigènes intervenant dans la réaction immunitaire a suscité de nombreux travaux dont les résultats sont exposés ici.Les antigènes sont représentés par les tissus du ver luimême (antigènes somatiques) ou par ses excrétions (antigènes métaboliques). La résistance à l'agression parasitaire peut être obtenue en employant soit des vers vivants (infestation par de très petites quantités de parasites, ou par des larves irradiées) soit des broyats de vers totaux ou des extraits de leurs sécrétions.L'administration d'antigènes peut conduire a une vaccination dans les cas favorables mais aussi à un état de tolérance.La connaissance exacte et la maitrise de ces facteurs, examinés ici, devraient conduire a la vaccination des animaux contre leurs parasites.

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Riassunto Gli animali portatori di parassiti sviluppano una resistenza al parassita stesso; la natura ed il ruolo degli antigeni che intervengono nella reazione immunitaira sono l'argomento di numerosi lavori i cui risultati sono que esposti.Gli antigeni sono costituiti dai tessuti del verme stesso (antigeni somatici), oppure dai suoi escreti (antigeni metabolici). La resistenza all'aggressione parassitaria puo essere ottenuta sia impiegando vermi vivi (infezione con quantita di parassiti molto piccole o con larve irradiate), sia ammassi di vermi interi o estratti dai loro secreti. La somministrazione di antigeni puo portare nei casi favorevoli ad una vaccinazione ma anche ad uno stato di tolleranza. La conoscenza esatta ed il controllo dei fattori qui esaminati, dovrebbero portare alla vaccinazione degli animali control loro parassiti.

     

Immunology of helminth infections, with special reference to immunopathology.

Immune responses resulting in immunity to infection or disease, share the same basic humoral and cellular mechanisms. While immunity to helminth infection has evolved to mediate rapid elimination of the parasite, the strategies evolved by the parasites themselves aim to delay this rejection process and ensure the survival and distribution of their progeny. Ineffective or incomplete immunity results in persistence of parasites or their products within the host tissues, inappropriate or chronic stimulation by parasite antigens, hyper-reactivity and tissue damage or immunopathology. A long standing classification by Gell and Coombs identifies four major types of hypersensitivity responses accounting for most of the immunopathogenesis, three of which are mediated by antibody and one, delayed type hypersensitivity (DTH), by T cells. This paper aims to give a short review of these four classical hypersensitivity reactions with particular reference to infections of large animals with helminth parasites. In addition, in view of the functionally different helper T cell subsets now identified, the existing DTH response is redefined as DTH Type 1 (Th-1 mediated) and two new classes of T cell-dependent DTH responses are proposed; DTH Type II, associated with the Th-2 type cytokines IL-4 and IL-5 and eosinophilic granuloma formation, and DTH Type III, associated with IL-4 and TGF-beta and fibrosis. Finally, some implications of immunopathology on parasite control strategies are discussed.