Pathogenicity of cyathostome infection

Cyathostomes are now the principle parasitic pathogen of the horse: a remarkable transformation during the last 25 years from virtual obscurity to focus of attention in equine parasitology. This rise to prominence coincides with the marked decrease in prevalence of large strongyle infections as a result of widespread use of modern anthelmintic compounds. On the basis that strongyle-associated diseases continue to commonly occur in the absence of these large strongyle species, clinical attention has turned to the pathogenicity of cyathostomes. Although many horses harbour burdens of tens of thousands of cyathostomes without developing detectable illness, these parasites can result in an inflammatory enteropathy affecting the caecum and colon. Although the principle clinical effect of cyathostomosis is weight loss, affected individuals may exhibit other signs including diarrhoea and/or subcutaneous oedema and/or pyrexia. Clinical cyathostomosis occurs more commonly in young horses in late winter/early spring but there is lifelong susceptibility to cyathostomes and they can cause clinical disease in any age of horse during any season. Animals with cyathostomosis often develop hypoalbuminaemia and/or neutrophilia but there are no clinicopathological features specific for the disease. Experimental infections with cyathostomes have resulted in both clinical and pathological features similar to those of naturally-occuring cyathostomosis cases. From the experimental infection studies, it is evident that cyathostomes are pathogenic at times of both penetration into and emergence from the large intestinal mucosa. An unusual feature of cyathostome biology is the propensity for arrested larval development within the large intestinal mucosa for more than 2 years. From limited studies it appears that this arrested larval development is favoured by: feedback from luminal to mucosal worms; larger size of challenge dose of larvae and trickle (versus single bolus) infection. During arrested larval development cyathostomes have minimal susceptibility to all anthelmintic compounds, thus, limiting the effectiveness of therapeutic and/or control strategies. Although, the relative importance of individual cyathostomes is not known, the development of species-specific DNA methods for identification of cyathostomes provides a means by which the pathogenicity of different species might be established.

Global warming is changing the dynamics of Arctic host-parasite systems

Global climate change is altering the ecology of infectious agents and driving the emergence of disease in people, domestic animals, and wildlife. We present a novel, empirically based, predictive model for the impact of climate warming on development rates and availability of an important parasitic nematode of muskoxen in the Canadian Arctic, a region that is particularly vulnerable to climate change. Using this model, we show that warming in the Arctic may have already radically altered the transmission dynamics of this parasite, escalating infection pressure for muskoxen, and that this trend is expected to continue. This work establishes a foundation for understanding responses to climate change of other host-parasite systems, in the Arctic and globally.

Canine pulmonary angiostrongylosis: an update

Canine pulmonary angiostrongylosis is an emerging snail-borne disease causing verminous pneumonia and coagulopathy in dogs. The parasite is found in Europe, North and South America and Africa, covering tropical, subtropical and temperate regions. Its distribution has been characterised by isolated endemic foci, with only sporadic occurrences outside these areas. In the last two decades, the literature has been dominated by several case reports and small case series describing sporadic disease in old or new endemic areas. Case reports and experimental studies with high doses of infective third stage larvae may not reflect what happens under field conditions. There is insufficient understanding of the spread of infection and the dynamic consequences of this parasite in the canine population. This review discusses the biology, epidemiology, clinical aspects and management of canine pulmonary angiostrongylosis.

Angiostrongylus vasorum infection in 23 dogs (1999-2002)

Angiostrongylosis was diagnosed in 23 dogs presenting to the Queen Mother Hospital for Animals between June 1999 and August 2002. The animals' clinical records were reviewed retrospectively and certain risk factors were compared with a control population of 3407 dogs. Twenty-two of the 23 dogs were from south-east England and dogs from Surrey (n=8) were significantly overrepresented. There were also significantly more Cavalier King Charles spaniels (n=5) and Staffordshire bull terriers (n=5) among the affected dogs than in the control group. The median age of affected dogs was 10 months (range five to 90 months). The most common presenting signs were cough (65 per cent), dyspnoea (43 per cent), haemorrhagic diathesis (35 per cent) and collapse (26 per cent). Four dogs were thrombocytopenic and eight had significant prolongations in prothrombin time and/or activated partial thromboplastin time. Thoracic radiographs were abnormal in 18 of 19 dogs. A variety of changes were observed, the most typical being a patchy alveolar-interstitial pattern affecting the dorsocaudal lung fields. Angiostrongylus vasorum larvae were found in seven of 10 bronchoalveolar lavage specimens and 19 of 19 faecal samples. Three dogs died shortly after admission to the hospital. The remainder were successfully treated with fenbendazole at a dose of 50 mg/kg for five to 21 days. A vasorum should now be considered endemic to south-east England.

Canine angiostrongylosis: a review

Angiostrongylus vasorum has been recognised as a cause of respiratory and circulatory distress among dogs in southwestern France for more than a decade, and the nematode now appears to be of increasing importance in the British Isles and Denmark. The aim of this review is to give a concise account of present knowledge of this intriguing parasitosis.

Lungworms and gastrointestinal parasites of domestic cats: a European perspective

With the exception of Aelurostrongylus abstrusus, feline lungworms have been poorly studied. Information on their distribution is patchy and mostly limited to case reports. In this study, the occurrence of feline lungworms and co-infecting gastrointestinal parasites has been investigated in 12 European countries (i.e. Austria, Belgium, Bulgaria, France, Greece, Hungary, Italy, Portugal, Romania, Spain, Switzerland and the United Kingdom). An average of 10 domestic cats, with regular outdoor access, was sampled each month for 12months, and freshly passed faeces were collected. Stools were processed using a McMaster assay and a quantitative Baermann-Wetzel method. Animals positive for lungworms and/or gastrointestinal parasites were treated with a formulation containing fipronil, (S)-methoprene, eprinomectin, and praziquantel (Broadline®, Merial), and re-sampled 28days post-treatment. The association between lungworm infection and risk factors was analysed using statistical medians/means and the efficacy of the treatment against each lungworm species was assessed. Of 1990 cats sampled, 613 (30.8%) were positive for at least one parasite, while 210 (10.6%) were infected by lungworms. The prevalence of lungworm infection varied between the sampled sites, with the highest recorded in Bulgaria (35.8%) and the lowest in Switzerland (0.8%). None of the cats from Austria or the United Kingdom were infected by lungworms. Aelurostrongylus abstrusus was the species most frequently detected (78.1%), followed by Troglostrongylus brevior (19.5%), Eucoleus aerophilus (14.8%) and Oslerus rostratus (3.8%). The overall efficacy of the treatment was 99% for A. abstrusus and 100% for T. brevior, O. rostratus and E. aerophilus. Data presented provide a comprehensive account of the diagnosis, epidemiology and treatment of feline lungworms in Europe, as well as of the occurrence of co-infections by gastrointestinal parasites.

Feline aelurostrongylosis and canine angiostrongylosis: a challenging diagnosis for two emerging verminous pneumonia infections

Aelurostrongylus abstrusus and Angiostrongylus vasorum (Nematoda, Metastrongyloidea) are causative agents of verminous feline and canine pneumonia. Both are presently emerging in several geographical areas and are of major clinical importance. Given the range of parasitic and non-parasitic pathogens which may cause cardio-respiratory distress in dogs and cats, the unequivocal specific diagnosis of both diseases is pivotal for unravelling their epidemiology and central to therapy and control. Several conventional clinico-pathologic, diagnostic imaging and parasitological approaches are currently used in practice, but all have major limitations in the specific diagnosis of these diseases. Serological methods have shown promise in the diagnosis of A. abstrusus and A. vasorum infections, but no clinically useful tests are currently available. Additionally, there have been major advances in the development of novel molecular diagnostic tools for feline aelurostrongylosis, but efforts to develop molecular diagnostic tests are still preliminary for angiostrongylosis. This article provides a review of A. abstrusus and A. vasorum infections in cats and dogs, focusing on the advantages and shortcomings of classical diagnostic methodologies and on present diagnostic advances as well as future perspectives instrumental to epidemiological and clinical studies.

Pharmacology of anthelmintic resistance in cyathostomes: will it occur with the avermectin/milbemycins?

Anthelmintic-resistance has emerged as a problem in several animal industries. In the horse, cyathostome resistance to all available treatments except for the avermectin/milbemycins means that these drugs provide the cornerstone of control. Ivermectin has been available for several years; the related compound moxidectin is more recent. Although we do not know for sure, aspects of moxidectin such as its persistent action and its efficacy against mucosal stages of cyathostomes, may enhance the rate of development of resistance. On the other hand, selection pressure would be reduced if the persistence of moxidectin allows it to be used less frequently in the field. Reduced anthelmintic usage and surveillance of egg reappearance period are the most useful tools in managing resistance.

Bighorn sheep pneumonia: sorting out the cause of a polymicrobial disease

Pneumonia of bighorn sheep (Ovis canadensis) is a dramatic disease of high morbidity and mortality first described more than 80 years ago. The etiology of the disease has been debated since its initial discovery, and at various times lungworms, Mannheimia haemolytica and other Pasteurellaceae, and Mycoplasma ovipneumoniae have been proposed as primary causal agents. A multi-factorial "respiratory disease complex" has also been proposed as confirmation of causation has eluded investigators. In this paper we review the evidence for each of the candidate primary agents with regard to causal criteria including strength of association, temporality, plausibility, experimental evidence, and analogy. While we find some degree of biological plausibility for all agents and strong experimental evidence for M. haemolytica, we demonstrate that of the alternatives considered, M. ovipneumoniae is the best supported by all criteria and is therefore the most parsimonious explanation for the disease. The strong but somewhat controversial experimental evidence implicating disease transmission from domestic sheep is consistent with this finding. Based on epidemiologic and microbiologic data, we propose that healthy bighorn sheep populations are naïve to M. ovipneumoniae, and that its introduction to susceptible bighorn sheep populations results in epizootic polymicrobial bacterial pneumonia often followed by chronic infection in recovered adults. If this hypothesized model is correct, efforts to control this disease by development or application of vectored vaccines to Pasteurellaceae are unlikely to provide significant benefits, whereas efforts to ensure segregation of healthy bighorn sheep populations from M. ovipneumoniae-infected reservoir hosts are crucial to prevention of new disease epizootics. It may also be possible to develop M. ovipneumoniae vaccines or other management strategies that could reduce the impact of this devastating disease in bighorn sheep.

Historical perspective of cyathostomes: prevalence, treatment and control programs

Small strongyles are highly prevalent in horses and can be found worldwide. Even though over 50 species of these parasites have been described, about 10 species comprise the bulk of the total number present in horses. Efforts to control small strongyles and other equine internal parasites have been undertaken for many years. Some of the early medications and control measures provided questionable activity against endoparasites; whether effective or not, they could be detrimental to the horse. Beginning in the early 1900s, scientific effort was used to evaluate activity of antiparasitic compounds. Only a relatively low number of classes of compounds has been used for parasite control. Progressively, in time, newer drugs have become broad-spectrum, safer, and available in lower dose rates than previously. With extensive use of parasiticides, small strongyles have been found to be resistant to all commercially-available classes of compounds except the macrocyclic lactones. Innovative parasite-control programs, relying less on drugs, need to be developed.

Natural infections of Crenosoma vulpis and Angiostrongylus vasorum in dogs in Atlantic Canada and their treatment with milbemycin oxime

Milbemycin oxime was used to treat dogs with natural infections of the fox lungworm, Crenosoma vulpis and the French heartworm, Angiostrongylus vasorum. Crenosomosis was identified in 42 of 202 dogs with clinical signs of coughing, dyspnoea or exercise intolerance by a Baermann analysis of faecal samples taken between October 2000 and October 2001. It occurred throughout Atlantic Canada (New Brunswick, Newfoundland, Nova Scotia and Prince Edward Island). The clinical signs resolved and shedding of larvae in faeces ceased in all 32 Crenosoma-infected dogs given a single oral dose of 0.5 mg/kg milbemycin oxime for which the results of faecal examinations were available. Angiostrongylosis was identified in 16 of the 202 dogs and was restricted to the Avalon peninsula of Newfoundland, where 67 dogs were tested. The clinical signs resolved and shedding of larvae ceased in 14 of the 16 dogs treated with four, weekly oral doses of 0.5 mg/kg milbemycin oxime. One dog with severe clinical signs died during the course of treatment and one owner failed to provide a faecal sample from their dog but reported that the clinical signs had resolved.

An annotated checklist by genus and species of 93 species level names for 51 recognized species of small strongyles (Nematoda: Strongyloidea: Cyathostominea) of horses, asses and zebras of the world

The results of an international collaborative effort to prepare a recommended list of scientific names for the small strongyles (Nematoda: Strongyloidea: Cyathostominea) of horses, donkeys and zebras are reported. Fifty-one valid species are recognized in 13 genera, including Cyathostomum, Coronocyclus, Cylicodontophorus, Cylicocyclus, Cylicostephanus, Skrjabinodentus, Tridentoinfundibulum, Petrovinema, Poteriostomum, Parapoteriostomum, Hsiungia, Cylindropharynx and Caballonema. In addition, 42 other species level names are listed as synonyms of the 51 recognized species or as species inquirendae (10 species) or nomen nudum (one species). Numerous annotations provide information on the nomenclatural and systematics history, current status and additional studies needed.

Faecal egg count reduction test for assessing anthelmintic efficacy: average versus individually based estimations

The faecal egg count reduction (FECR) in faeces is the most widely used method to assess the efficacy of anthelmintics against gastrointestinal strongyles. Several methods are used and they yield different efficacy values. They give important weight to those animals which excrete the majority of eggs, before or after treatment. We propose using individual animal FECR tests that give equal weight to every tested host. The first method is based on a before and after treatment without untreated controls, whereas the second one takes into account the use of non-treated control hosts. Confidence interval at P = 0.95 were established on bootstrap resamples for both individual-based methods. The individual-based FECR presented lower values than the average-based FECR in most cases. The individual FECR provided reliable evaluation when egg counts were over 300 eggs/g and when at least 10 animals were tested.

Quantitative trait loci (QTL) mapping of resistance to strongyles and coccidia in the free-living Soay sheep (Ovis aries)

A genome-wide scan was performed to detect quantitative trait loci (QTL) for resistance to gastrointestinal parasites and ectoparasitic keds segregating in the free-living Soay sheep population on St. Kilda (UK). The mapping panel consisted of a single pedigree of 882 individuals of which 588 were genotyped. The Soay linkage map used for the scans comprised 251 markers covering the whole genome at average spacing of 15cM. The traits here investigated were the strongyle faecal egg count (FEC), the coccidia faecal oocyst count (FOC) and a count of keds (Melophagus ovinus). QTL mapping was performed by means of variance component analysis so that the genetic parameters of the study traits were also estimated and compared with previous studies in Soay and domestic sheep. Strongyle FEC and coccidia FOC showed moderate heritability (h(2)=0.26 and 0.22, respectively) in lambs but low heritability in adults (h(2)<0.10). Ked count appeared to have very low h(2) in both lambs and adults. Genome scans were performed for the traits with moderate heritability and two genomic regions reached the level of suggestive linkage for coccidia FOC in lambs (logarithm of the odds=2.68 and 2.21 on chromosomes 3 and X, respectively). We believe this is the first study to report a QTL search for parasite resistance in a free-living animal population and therefore may represent a useful reference for similar studies aimed at understanding the genetics of host-parasite co-evolution in the wild.

Rotational grazing for control of gastrointestinal nematodes of goats in a wet tropical environment

A preliminary experiment involving contamination of pasture plots with eggs of Haemonchus contortus, Trichostronglyus colubriformis and Oesophagostomum columbianum every month for a year established that in the tropical environment of the Pacific island of Tongatapu, hatching and development of all species was rapid and continuous, with a short survival on pasture (3-7 weeks) of the resulting infective larvae. These results indicated that a rotational grazing system consisting of ten paddocks grazed in sequence for 3.5 days at a time may permit a reduction in the frequency of anthelmintic treatment of goats. In comparison with an adjacent set-stocked flock which required treatment on three occasions during the year when mean flock egg counts exceeded 2000 eggs per gram (EPG), rotationally grazed goats generally maintained mean egg counts of less than 1000 EPG. Anthelmintic treatment was only given to rotationally grazed goats individually as they kidded, and there were indications that even this precaution was unnecessary. Because of the expense of frequent anthelmintic treatment and the resulting selection of strains of anthelmintic-resistant nematodes, rotational grazing of small ruminants through fencing, tethering or herding deserves further investigation as a nematode control option in wet tropical environments.

The use of nuclear ribosomal DNA markers for the identification of bursate nematodes (order Strongylida) and for the diagnosis of infections

Many bursate nematodes are of major importance to animal health. Animals are often parasitized by multiple species that differ in their prevalence, relative abundance and/or pathogenicity. Implementation of effective management strategies for these parasites requires reliable methods for their detection in hosts, identification to the species level and measurement of intensity of infection. One major problem is the difficulty of accurately identifying and distinguishing many species of bursate nematode because of the remarkable morphological similarity of their eggs and larvae. The inability to identify, with confidence, individual nematodes (irrespective of their life-cycle stage) to the species level by morphological methods has often led to a search for species-specific genetic markers. Studies over the past 15 years have shown that sequences of the internal transcribed spacers of ribosomal DNA provide useful genetic markers, providing the basis for the development of PCR-based diagnostic tools. Such molecular methods represent powerful tools for studying the systematics, epidemiology and ecology of bursate nematodes and, importantly, for the specific diagnosis of infections in animals and humans, thus contributing to improved control and prevention strategies for these parasites.

Efficacy and safety of imidacloprid/moxidectin spot-on solution and fenbendazole in the treatment of dogs naturally infected with Angiostrongylus vasorum (Baillet, 1866)

A randomized, blinded, controlled multicentre field trial study was conducted to evaluate the efficacy and safety of imidacloprid 10%/moxidectin 2.5% spot-on solution and fenbendazole in treating dogs naturally infected with Angiostrongylus vasorum. Dogs were randomly treated either with a single dose of 0.1 ml/kg bodyweight of imidacloprid 10%/moxidectin 2.5% spot-on solution or with 25 mg/kg bodyweight fenbendazole per os for 20 days. The study period was 42 days with dogs being examined on days 0, 7 and 42. The primary efficacy parameter was the presence of L1 larvae in faecal samples evaluated by a Baermann test from three consecutive days. Thoracic radiographs performed on each visit were being taken as a paraclinical parameter to support the results of the Baermann test. Twenty-seven dogs in the imidacloprid/moxidectin group and 23 dogs in the fenbendazole group completed the study according to protocol. The efficacies of the two treatment protocols were 85.2% (imidacloprid/moxidectin) and 91.3% (fenbendazole) with no significant difference between treatment groups. On radiographic evaluation pulmonary parenchyma showed similar improvement in each group. No serious adverse effects to treatment were recorded: most of the minor adverse effects were gastrointestinal such as diarrhea (nine dogs), vomitus (eight dogs) and salivation (three dogs). In general, these adverse effects were of short duration (1-2 days) within the first few days after treatment start and required little or no treatment. This prospective study demonstrates that both treatment protocols used are efficacious under field conditions, that treatment of mildly to moderately infected dogs with either of these protocols is safe and yields an excellent prognosis for recovering from the infection.

The common frog (Rana temporaria) as a potential paratenic and intermediate host for Angiostrongylus vasorum

Common frogs (Rana temporaria) were exposed either to third-stage larvae (L3) or to first-stage larvae (L1) of Angiostrongylus vasorum. Following exposure to L3, viable larvae could be detected in the frogs for at least 2 weeks. Following exposure to L1, the frogs developed viable L3 in their tissues within 30 days. In a test of the infectivity of these larvae, one fox was fed frogs previously infected with L3 and another fox was fed frogs previously infected with L1. On autopsy it was found that adult A. vasorum populations had been established in both foxes. Thus, it could be concluded that frogs can act not only as paratenic hosts but also as intermediate hosts for A. vasorum.

A multiplex PCR assay for differentiating economically important gastrointestinal nematodes of cattle

A multiplex polymerase chain reaction (PCR) test was developed for identifying gastrointestinal (GI) nematodes that commonly infect cattle. This assay was developed using adult-derived genomic DNA and shown capable of discriminating parasite eggs from the feces of experimentally-infected animals at both the species and genus levels. Sequence data from internal (ITS) and external (ETS) transcribed spacers of the ribosomal DNA (rDNA) repeats as well as the 3'-end of the small subunit rDNA and 5'-end of the large subunit rDNA were used to generate five primer sets which, when used simultaneously in a multiplex PCR, produce a unique electrophoretic DNA banding pattern characterized by a single DNA fragment for Ostertagia ostertagi (257bp), Haemonchus placei (176bp), Oesophagostomum radiatum (329bp), Trichostrongylus colubriformis (243bp) and Cooperia oncophora (151bp). In a similar manner, the constructed primer sets amplified DNA from Ostertagia lyrata, Haemonchus contortus, Trichostrongylus axei, Cooperia surnabada and Cooperia punctata. With respect to H. contortus, a closely migrating doublet was generated suggesting size heterogeneity in the ETS which is consistent with multiple rDNA repeat units within this species. PCR analyses using mixtures of monospecifically-purified nematode eggs indicated a sensitivity of less than 0.5 egg-DNA equivalent per species. Although, not designed as a quantitative technique, relative PCR signal intensities corresponded to relative egg burdens within the DNA samples from mixed species of eggs.

Parastrongylus (=Angiostrongylus) cantonensis now endemic in Louisiana wildlife

Parastrongylus (=Angiostrongylus) cantonensis, a lung worm of rats, was first reported in the United States in 1987, with a probable introduction by infected rats from ships docking in New Orleans, Louisiana, during the mid-1980s. Since then, it has been reported in nonhuman primates and a boy from New Orleans, and in a horse from Picayune, Mississippi, a distance of 87 km from New Orleans. Parastrongylus cantonensis infection is herein reported in a lemur (Varencia variegata rubra) from New Iberia, Louisiana, a distance of 222 km from New Orleans, and in a wood rat (Neotomafloridanus) and in 4 opossums (Didelphis virginiana) from Baton Rouge, Louisiana, a distance of 124 km from New Orleans. The potential of a great variety of gastropods serving as intermediate hosts in Louisiana may pose a threat to wildlife as well as to domesticated animals in the areas where infected Norway rats (Rattus norvegicus) are present.

Brain and spinal cord haemorrhages associated with Angiostrongylus vasorum infection in four dogs

Multifocal haemorrhages associated with Angiostrongylus vasorum infection were observed in the central nervous system of four dogs with neurological signs including depression, seizures, spinal pain and paresis. In magnetic resonance images the majority of the lesions were isointense or slightly hyperintense in T1-weighted images, hyperintense in T2-weighted images and hypointense in T2*-weighted (gradient echo) images, compatible with haemorrhages more than seven days old. Lesions were found in the brain of three of the dogs and in the spinal cord of two. The cerebrospinal fluid contained high concentrations of protein and evidence of erythrophagia. All the dogs had coagulopathy and pulmonary haemorrhage of varying severity. A vasorum larvae were detected in the faeces of each of the dogs. Neural A vasorum was confirmed at postmortem examination in two dogs.

Species-specific amplification by PCR of ribosomal DNA from some equine strongyles

The first and second internal transcribed spacer sequences of 28 morphologically-defined species of horse strongyle were characterized, and specific oligonucleotide primers were designed for some species based on the nucleotide differences. Utilizing these primers, a PCR approach was developed for the specific amplification of ribosomal DNA of Strongylus vulgaris, Cyathostomum catinatum, Cylicocyclus nassatus, Cylicostephanus longibursatus or Cylicostephanus goldi. The method allowed the species-specific amplification of parasite DNA derived from faecal samples and/or copro-cultures, demonstrating the potential of the approach for the diagnosis of equine strongyloidosis. The establishment of this PCR assay also has implications for studying the biology and epidemiology of equine strongyles and anthelmintic resistance using faecal egg count reduction tests.

Climate change and the epidemiology of protostrongylid nematodes in northern ecosystems:Parelaphostrongylus odocoileiandProtostrongylus stilesiin Dall's sheep (Ovis d. dalli)

We describe the epidemiology of the protostrongylid parasitesParelaphostrongylus odocoileiandProtostrongylus stilesiin Dall's sheep (Ovis dalli dalli) from the Mackenzie Mountains, Northwest Territories, Canada (65 °N; 128 °W). Peak numbers of 1st-stage larvae of both parasites were shed by Dall's sheep on their winter range from March until May. In larval development experiments in the Mackenzie Mountains, peak numbers of infective 3rd-stage larvae ofP. odocoileiwere available in gastropod intermediate hosts in August–September. For both protostrongylids, the majority of transmission likely occurs on the winter range, with infection of gastropods when they emerge from hibernation in spring, and infection of Dall's sheep upon their return in fall. We validated a degree-day model for temperature-dependent development of larvalP. odocoileiin gastropods, and applied degree-day models to describe and predict spatial and temporal patterns in development ofP. odocoileiandP. stilesiin northern North America. Temperature-dependent larval development may currently limit northward range expansion ofP. odocoileiinto naïve populations of Dall's sheep in the Arctic, but climate warming may soon eliminate such constraints. In Subarctic regions where bothP. odocoileiandP. stilesiare endemic, the length of the parasite ‘growing season’ (when temperatures were above the threshold for larval development) and amount of warming available for parasite development has increased over the last 50 years. Further climate warming and extension of the seasonal window for transmission may lead to amplification of parasite populations and disease outbreaks in host populations.

Immunity in equine cyathostome infections

Defining the characteristics of immunity and immune responses to equine cyathostome infections is clearly important to advancing our understanding of the development of these nematodes within the host, the clinical conditions attributed to them, and in developing more rational and novel strategies for their control. Nonetheless, little is currently known on this topic. Current data based on field observations, worm burdens and fecal egg counts suggest that horses acquire a resistance to cyathostome infection with age. This response is slow to develop and incomplete in that most horses regardless of age harbor significant populations of these nematodes. More convincing evidence has been obtained from experimental infections which indicate that mature horses previously exposed to infection are resistant to re-infection and this resistance is directed at all stages of the parasite life cycle. Further, some immunity against the developing stages within the mucosa appears to require less exposure and occurs in younger animals. Some non-specific events which induce expulsion of all species of lumenal dwelling nematodes also appear to take place post-infection with L3. Antibodies have been detected in limited studies against somatic extracts of adult worms. Not surprisingly, titers of these antibodies do not correlate resistance to re-infection. Serendipitous observations have, however, associated a greater expression of the gene for IL-4 with the spontaneous expulsion of lumenal parasites. The development of a usable model is required to further advance our knowledge in this area.

The spatial ecology of free-ranging domestic pigs (Sus scrofa) in western Kenya

BACKGROUND

In many parts of the developing world, pigs are kept under low-input systems where they roam freely to scavenge food. These systems allow poor farmers the opportunity to enter into livestock keeping without large capital investments. This, combined with a growing demand for pork, especially in urban areas, has led to an increase in the number of small-holder farmers keeping free range pigs as a commercial enterprise. Despite the benefits which pig production can bring to a household, keeping pigs under a free range system increases the risk of the pig acquiring diseases, either production-limiting or zoonotic in nature. This study used Global Positioning System (GPS) technology to track free range domestic pigs in rural western Kenya, in order to understand their movement patterns and interactions with elements of the peri-domestic environment.

RESULTS

We found that these pigs travel an average of 4,340 m in a 12 hr period and had a mean home range of 10,343 m(2) (range 2,937-32,759 m(2)) within which the core utilisation distribution was found to be 964 m(2) (range 246-3,289 m(2)) with pigs spending on average 47% of their time outside their homestead of origin.

CONCLUSION

These are the first data available on the home range of domestic pigs kept under a free range system: the data show that pigs in these systems spend much of their time scavenging outside their homesteads, suggesting that these pigs may be exposed to infectious agents over a wide area. Control policies for diseases such as Taenia solium, Trypanosomiasis, Trichinellosis, Toxoplasmosis or African Swine Fever therefore require a community-wide focus and pig farmers require education on the inherent risks of keeping pigs under a free range system. The work presented here will enable future research to incorporate movement data into studies of disease transmission, for example for the understanding of transmission of African Swine Fever between individuals, or in relation to the life-cycle of parasites including Taenia solium.