F Guy

University of Liverpool, Liverpool, ENG, United Kingdom

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Publications (14)30.39 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The parasite Neospora caninum is an important cause of abortion in cattle world-wide. Chronically infected dams transmit the parasite transplacentally and infected foetuses may be aborted or born chronically infected but clinically normal. Chronically infected cows repeatedly transmit the parasite to foetuses in several pregnancies and some may abort more than once suggesting that the immune response in these cattle is compromised during pregnancy. To investigate the nature of the immune response in chronically infected cattle, five naturally, chronically infected cows were challenged with N. caninum tachyzoites at 10 weeks of gestation. No foetopathy occurred and all five delivered live calves at full-term. In four naive pregnant cows challenged at the same time, all four foetuses died within 3-5 weeks of challenge. Of the five live calves born to the chronically infected challenged cows, three were transplacentally infected with N. caninum. The kinetics of the maternal anti-N. caninum antibody responses during gestation suggested that these transplacental infections were not the result of the superimposed challenge, but the result of the recrudescence of the maternal chronic infection-which occurred concurrently in non-challenged, chronically infected pregnant controls. These data provide the first experimental evidence that protective immunity occurs in neosporosis. They also suggest that whilst immunity to a pre-existing infection will protect against an exogenous challenge, this protective immunity will not prevent transplacental infection. This implies that a subtle form of concomitant immunity exists in chronically infected cattle and has important implications for vaccine development.
    International Journal for Parasitology 10/2003; 33(10):1059-65. · 3.64 Impact Factor
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    ABSTRACT: Nine cows which were naturally and persistently infected with Neospora caninum were housed and observed intensively throughout pregnancy. No recrudescence of a latent infection was detected by PCR tests on maternal blood but fetal infection, implying a recrudescence of maternal parasitosis, was associated with a marked increase in maternal antibody. The increase occurred in the second half of pregnancy in five cows which infected their calves, and before mid-pregnancy in one cow which aborted. There was no change in the avidity of the antibody, which remained high and characteristic of long-term infection. In three infected cows that gave birth to uninfected calves there was no marked increase in maternal antibody. Antigen-specific interferon gamma responses of peripheral blood mononuclear cells were observed in all the infected cattle but they did not vary significantly either during pregnancy, or whether the cows did or did not infect their calves, although the responses were consistently higher in the latter. There was no change in the plasma concentrations of cortisol or acute phase proteins associated with the recrudescence of the parasite. Three uninfected cows housed with the infected cows remained uninfected throughout the experiment. No immunosuppressive event was detected which might have provoked parasite recrudescence but the acute antibody rise associated with transplacental infection provides a valuable, non-invasive marker for further studies to investigate the cause and consequences of parasite recrudescence in N caninum infection in cattle.
    The Veterinary record 11/2001; 149(15):443-9. · 1.80 Impact Factor
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    ABSTRACT: Onchocerciasis is a debilitating parasitic infection caused by the filarial nematode Onchocerca volvulus. Infections are chronic, and persistence of the parasites for several years argues for highly adapted mechanisms of immune evasion. Due to the restricted host repertoire of O. volvulus, we have used the cattle parasite Onchocerca ochengi to investigate the nature of immunomodulation underpinning these long-term infections. Cattle were infected with a single inoculation of 350 infective-stage larvae under laboratory conditions (n = 6). Intradermal nodules containing immature adult worms were detected from 110 days postinfection, and microfilariae in skin were detected from day 280 postinfection. Parasite-specific responses during early infection were nonpolarized with respect to the major Th cytokines (interleukin-4 [IL-4], IL-2, and gamma interferon [IFN-gamma]) produced by antigen-stimulated peripheral blood mononuclear cells (PBMC) or serum antibody isotypes. Antigen-induced proliferation of PBMC peaked shortly after exposure and remained high during the prepatent infection. As the parasites matured and animals developed patent infections, there was a profound down-regulation of lymphoproliferation, accompanied by sharp falls in the expression of both IL-4 and IFN-gamma and a gradual decline in IL-2. Levels of immunoglobulin G2 (IgG2) fell, while those of IgG1 remained high. We conclude that neither a classical Th2 response nor a simple Th1-to-Th2 switch is sufficient to explain the immunomodulation associated with patent Onchocerca infections. Instead, there is an initial Th0 response, which matures into a response with some, but not all of the features of a Th2 response. The natural host-parasite relationship of O. ochengi in cattle may be useful as both a descriptive and predictive tool to test more refined models of immunomodulation in onchocerciasis.
    Infection and Immunity 08/2001; 69(7):4313-9. · 4.07 Impact Factor
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    ABSTRACT: Three studies were conducted to investigate the transmission of Neospora caninum between cattle by the oral route. In the first study, six calves were dosed with 10(7)N caninum tachyzoites (NC LivB1) in colostrum and/or milk replacer on four occasions. In the second study, two calves and two cows were fed placental tissues from N caninum -infected cows, and, in the third study, seven uninfected calves were fostered onto N caninum -infected dams. In the first study, all six calves developed antibody responses and five calves developed antigen-specific lymphoproliferation responses, including two calves initially challenged at 1 week of age. No evidence of N caninum infection was found in the brain or heart of these calves by histology or polymerase chain reaction (PCR). In the second and third studies, there was no evidence of N caninum infection in any of the calves and cows. The results confirm that calves up to 1 week of age can be experimentally infected via the oral route, but suggest that this is not an important natural route of transmission for N caninum between cattle.
    Research in Veterinary Science 05/2001; 70(2):163-8. · 1.77 Impact Factor
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    ABSTRACT: The parasite, Neospora caninum is an important cause of abortion in cattle. It is transmitted vertically or horizontally and infection may result in abortion or the birth of a live, healthy but infected calf at full-term. Only a proportion of infected cattle abort and the pathogenesis of abortion is not understood. Groups of cattle were infected with 10(7) N. caninum tachyzoites intravenously at different times relative to gestation. Intravenous inoculation was chosen to reproduce the putative haematogenous spread of N. caninum following either recrudescence of endogenous infection or de novo infection. In all cattle, infection was accompanied by high gamma-interferon and lymphoproliferative responses, and a biased IgG2 response indicating that N. caninum infection is accompanied by a profound Th1 helper T cell-like response. Infection at 10 weeks gestation resulted in foetopathy and resorption of foetal tissues 3 weeks after infection in 5 out of 6 cows. Infection at 30 weeks gestation resulted in the birth of asymptomatic, congenitally-infected calves at full term in all 6 cows, whereas the 6 cows infected before artificial insemination gave birth to live, uninfected calves. These results suggest that the reason some cows abort is related to the time during gestation when they become infected or an existing infection recrudesces.
    Parasitology 11/2000; 121 ( Pt 4):347-58. · 2.36 Impact Factor
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    ABSTRACT: A commercially available serum antibody detection enzyme-linked immunosorbent assay for Neospora caninum in cattle was evaluated against an immunofluorescent antibody test (IFAT) by applying it to 397 sera from normal adult cattle, 352 sera from cattle which had recently aborted, and 422 sera from two herds which had a history of N caninum-associated abortions. It was evaluated in two laboratories and showed high reproducibility, repeatability and almost perfect or substantial agreement with the IFAT.
    The Veterinary record 12/1999; 145(20):571-5. · 1.80 Impact Factor
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    ABSTRACT: Neospora caninum was isolated in Vero cell culture from the brain of a stillborn calf. This isolate (designated NC-LivB1) is the first to be obtained from cattle in the United Kingdom and was confirmed as N. caninum by immunofluorescence with specific antibodies and by internal transcribed spacer 1 (ITS1) sequence analysis. Differences were found between NC-LivB1, other bovine isolates and canine isolates of N. caninum and closely related protozoal parasites, using random amplified polymorphic DNA polymerase chain reaction (RAPD - PCR) techniques.
    Research in Veterinary Science 09/1999; 67(1):103-5. · 1.77 Impact Factor
  • The Veterinary record 01/1998; 141(23):607. · 1.80 Impact Factor
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    ABSTRACT: An enzyme-linked immunosorbent assay (ELISA) to detect antibodies to Neospora species in cattle was developed. Whole formalin-fixed Neospora caninum (NC-Liverpool) tachyzoites were used as antigen and a monoclonal antibody to bovine immunoglobulin light chain and an anti-mouse horseradish peroxidase conjugate were used to reveal bound antibody. A panel of 46 sera, negative by the immunofluorescent antibody test (IFAT), were used in the ELISA at a serum dilution of 1:500 to calculate the negative cut-off value of OD405 = 0.77. There was a 95 per cent agreement between the results of the ELISA and the IFAT with 104 serum samples. The specificity and sensitivity of the ELISA were 96 per cent and 95 per cent, respectively, when compared with the IFAT. No significant cross-reaction was observed with the sera from cattle infected experimentally with Toxoplasma gondii, Cryptosporidium parvum, Babesia divergens, Sarcocystis cruzi, Eimeria alabamensis or E bovis. A significantly modified version of the test is now commercially available.
    The Veterinary record 04/1997; 140(13):328-31. · 1.80 Impact Factor
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    The Veterinary record 05/1996; 138(17):419-20. · 1.80 Impact Factor
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    ABSTRACT: Neospora caninum is an apicomplexan, protozoan parasite, which causes severe disease in dogs and cattle. It has previously been isolated only in the United States. A 5-week-old Boxer pup with a progressive hindlimb paresis was diagnosed as suffering from neosporosis on the basis of clinical signs and the presence of anti-Neospora antibodies in it, 2 litter-mates and its dam. Despite treatment with sulphonamides, the pup was euthanased 3 days later. The diagnosis of neosporosis was confirmed by immunohistochemical examination of muscle and CNS tissue sections from the pup. Parasites were isolated into Vero cell culture from the cerebrum, and confirmed as Neospora caninum by immunofluorescence with specific antibody, tachyzoite ultrastructure and 16S-like ribosomal RNA sequences. This isolate (designated NC-Liverpool) has been continuously passaged every 7-10 days. Its growth characteristics, ultrastructure and antigenic profile, as revealed by immunoblotting, have revealed no major differences from the American NC-1 isolate. Furthermore, no difference was seen when comparing the sequences of 16S-like ribosomal RNA and the ITS1 region of the two isolates.
    Parasitology 01/1996; 111 ( Pt 5):563-8. · 2.36 Impact Factor
  • The Veterinary record 12/1995; 137(22):566-7. · 1.80 Impact Factor
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    ABSTRACT: By means of an immunofluorescence antibody test (IFAT), using in vitro cultured parasites as antigen, antibodies to Neospora species at titres > or = 1/1280 were found in 11 of 120 Scottish cattle that had recently aborted but in only one of 97 cattle from herds in which there had been no recent abortions (P < 0.01). The specificity of the antibodies was confirmed by the lack of cross reactivity between samples with high titres to Neospora and toxoplasma antigen in a direct agglutination test, and by the absence of reactivity at > or = 1/640 in the IFAT of convalescent sera from cattle infected experimentally with Toxoplasma gondii, Sarcocystis cruzi, Eimeria bovis, E alabamensis, Cryptosporidium parvum and Babesia divergens. These results demonstrate that Neospora species infection occurs commonly in aborting cattle in Britain, and that the IFAT may be a useful tool for investigating the infection.
    The Veterinary record 05/1994; 134(16):405-7. · 1.80 Impact Factor
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    ABSTRACT: Of 163 dogs, randomly selected from those examined at the University of Liverpool Small Animal Hospital, 12.9 per cent had antibody titres > or = to 1/200 to Neospora caninum in an indirect fluorescent antibody test. None was apparently suffering clinical neosporosis. There was no association between the occurrence of neospora antibodies and either toxoplasma antibodies measured by the dye test, sex, age, type of feeding or the presence of other dogs in the household. Antibody was detected at titres > or = to 1/200 in nine breeds, suggesting that there is a substantial level of subclinical infection in British dogs.
    The Veterinary record 02/1993; 132(6):125-6. · 1.80 Impact Factor