D.D. Colwell

Parasites in Ungulates of Arctic North America and Greenland: A View of Contemporary Diversity, Ecology, and Impact in a World Under Change

Parasites play an important role in the structure and function of arctic ecosystems, systems that are currently experiencing an unprecedented rate of change due to various anthropogenic perturbations, including climate change. Ungulates such as muskoxen, caribou, moose and Dalls sheep are also important components of northern ecosystems and are a source of food and income, as well as a focus for maintenance of cultural traditions, for northerners. Parasites of ungulates can influence host health, population dynamics and the quality, quantity and safety of meat and other products of animal origin consumed by people. In this article, we provide a contemporary view of the diversity of nematode, cestode, trematode, protozoan and arthropod parasites of ungulates in arctic and subarctic North America and Greenland. We explore the intricate associations among host and parasite assemblages and identify key issues and gaps in knowledge that emerge in a regime of accelerating environmental transition.

The molecular epidemiology of Cryptosporidium and Giardia infections in coyotes from Alberta, Canada, and observations on some cohabiting parasites

Coyotes from southern Alberta and Saskatchewan, Canada, were examined for the presence of Giardia and Cryptosporidium and cohabiting helminths. Toxascaris was present in over 90% of the 70 animals examined, and Taenia sp. in 6.5-25% of the two groups of animals studied. Giardia (12.5-21.7%) and Cryptosporidium (0-17.4%) were also common and molecular characterisation revealed both zoonotic and host-adapted genotypes of Giardia, whereas the Cryptosporidium proved to be a variant of the canine species C. canis. The seasonal variation observed in the occurrence of Cryptosporidium may be related to stress-induced shedding of the parasite.

A laser-based method for measuring thermal nociception of cattle

We describe a method for measuring nociception in cattle using a CO(2) laser aimed at the caudal aspect of the metatarsi. In Experiment 1, infrared thermography showed that calves responded by lifting their legs when skin temperatures reached 45-55 degrees C. In Experiment 2a, the validity of the method was tested by comparing the response latencies of 14 calves to two power settings (2.25 W vs. 4.5 W) with each setting being applied six times. We found that both leg-lift latencies and tail-flick latencies were lower at the higher power setting, and the calves were more likely to respond by kicking than by simply moving the leg. The standard deviations between and within calves were smaller at the higher power setting, and the large within-calf variation means that at least three tests were required to obtain reliable measures that could differentiate between calves. In Experiment 2b, application of the laser at a range of power settings (2.0, 3.0, 4.0, 4.5, 5.0 and 5.5 W) on 16 calves showed that response latencies decreased as power increased up to 4.5 W, after which no further change occurred. In Experiment 3, the repeatability of the method was evaluated on nine measures with the high power setting (4.5 W). The coefficient of variation associated with repetition of the measures was 36%. In general, we found little change in response latencies with repeated use of the laser, except that responses on the second test tended to be shorter. Experiment 4 showed that ambient temperatures between 16 degrees C and 27 degrees C did not affect response latencies, but these were longer at temperatures of 7 degrees C. We suggest that the method is a useful way of measuring cattles sensitivity to nociception as the animals need not be restrained and the distance to the animal need not be closely controlled. However, to obtain accurate, valid and reliable measures it is necessary to use a high power setting (4.5 W) and take at least three consecutive measures of the response latency.

INFLUENCE OF PARASITICIDE TREATMENT ON KINETICS OF ANTIGEN SPECIFIC ANTIBODY RESPONSE IN CATTLE INFESTED WITH HYPODERMA LINEATUM (DIPTERA : OESTRIDAE)

The effect of parasiticide treatment on dynamics of antigen specific antibody responses to Hypoderma lineatum (De Villers) was investigated in naturally infested calves. Parasiticides were applied to cattle 1 month prior to, 1 week prior to, and coincident with the appearance of warbles in untreated calves from the same source herd. When cattle were treated approximately 1 month before warbles appeared in untreated control animals, antigen specific antibody levels increased for 25-34 days then declined to undetectable levels by approximately 75 days. Antigen specific antibody levels sharply declined in cattle treated 1 week prior to appearance of warbles in untreated controls. Treatment applied coincident with arrival of grubs on the back did not alter the antigen specific antibody profile, but reduced the relative magnitude of antigen specific antibodies present. Persistence of the antigen specific antibody following treatment will permit conduct of serological surveillance programmes.

Evaluation of diagnostic techniques for Anoplocephala perfoliata in horses from Alberta, Canada.

Accurate diagnosis of parasites within individual hosts remains a difficult task. Incorrect and/or inaccurate diagnosis restricts the potential for targeted treatment of individuals and limits our understanding of key epidemiological characteristics of potential pathogens of domestic stock. In this study, we compared the specificity and sensitivity of four diagnostic methods for determination of the presence and intensity of the cestode Anoplocephala perfoliata in horses. Over 400 horses from an abattoir in south-central Alberta were evaluated for the presence and number of cestodes. Thirty one horses were infected with 1 to >1000 worms. Diagnosis based upon faecal egg counts of horses with known numbers of worms was least accurate in detecting worm presence. Detection of circulating antibodies to the cestode was most sensitive using Western blot analysis (100%), but had lower specificity (87%). A serum-based ELISA had a lower sensitivity (70%) for detection of antibodies. A coproantigen ELISA had 74% sensitivity and 92% specificity, and there was a positive correlation between antigen concentration and tapeworm intensity. The coproantigen ELISA may have the potential as a diagnostic tool for determining the presence and intensity of this potentially pathogenic cestode.

Local and systemic cytokine responses during larval penetration in cattle experimentally infested with Hypoderma lineatum (Diptera: Oestridae)

Local and systemic cytokine responses were studied in 3 groups of cattle, with 4 animals each, experimentally infested with Hypoderma lineatum (De Villers) first instars (L1). The first group was undergoing a primary infestation (G-1), the second group was undergoing a secondary infestation (G-2) and the third group was infested for their third consecutive year (G-3). Cattle were infested with 25 L1 deposited on the skin. Blood and skin samples were taken at 0, 6, 12, 48, 96 and 144h post-infestation (h.p.i.). Interleukin 10 (IL-10), IL-4 and interferon gamma (IFN-gamma) production was studied by immunohistochemistry and sandwich ELISAs. IL-4(+) cells showed a significant increase at 6h.p.i. in both reinfested groups (G-2 and G-3) when compared with G-1. In all groups the number of IL-4(+) cells decreased significantly at 48h.p.i. IL-10(+) cells increased in G-1 at 6 and 48h.p.i., whereas in both reinfested groups increased at 12h.p.i. with a peak at 48h.p.i. IFN-gamma(+) cells showed a significant increment at 6h.p.i. in all groups, followed by a rapid descent at 12 (G-1 and G-2) and 48h.p.i. (G-3). Penetration of the skin by H. lineatum did not have any significant effect on IFN-gamma serum concentrations and, except for IL-10 there were no correlation between local production and serum concentrations of cytokines. The increase of both Th1 (IFN-gamma) and Th2-type cytokines (IL-4 and IL-10) indicates that bovine T-cell response during the first phases of the infestation by H. lineatum is apparently a Th0 response.

Immunohistochemical Characterization of Inflammatory Cells in the Skin of Cattle undergoing Repeated Infestations with Hypoderma lineatum (Diptera: Oestridae) Larvae

Cutaneous T- and B-cell responses were studied in three groups of cattle (n=4) after a primary (G1), secondary (G2) and tertiary (G3) experimental infestation with Hypoderma lineatum first instars (L1). Cattle were each infested with 25 L1 deposited onto the skin. Skin biopsies were taken at 0, 6, 12, 48, 96 and 144 h post infestation (hpi). The kinetics of infiltration of CD3(+), CD4(+) and CD8(+) T lymphocytes and B cells at the infestation site was evaluated immunohistochemically. The number and pattern of infiltration of CD3(+) T cells were similar in the different groups of animals, showing a progressive increase until 96 hpi. The number of CD4(+) T helper cells increased significantly at 96, 6 and 48 hpi in G1, G2 and G3, respectively. CD8(+) cytotoxic T-cell infiltration was similar in the different groups, except at 48 hpi when there was a significant difference between G1 and G3. The CD4:CD8 ratio showed predominance of CD4(+) cells throughout the response. The number of B cells increased with the number of previous infestations, with significant differences between G1 and G3 at 12 hpi. All of the cell types concentrated around the superficial and deep dermal vessels. During primary larval infestations there was a predominance of CD4(+) cells, whereas in cattle sensitized by previous infestations, B cells were most abundant in the infiltrate. These findings suggest that humoral immunity may play a significant role in bovine immunity to H. lineatum.