Diana J.L. Williams

Neospora caninum -associated abortion in cattle: the time of experimentally-induced parasitaemia during gestation determines foetal survival

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.

Immune responses to Neospora caninum and prospects for vaccination

Developing an effective vaccine against neosporosis presents several interesting challenges. The parasite is spread efficiently from mother to foetus over several generations, and naturally infected cattle do not appear to develop adequate protective immunity. Modulation of the immune response during pregnancy favours parasite survival and multiplication. However, induction of pro-inflammatory responses that are thought to be protective against Neospora caninum would be detrimental to the pregnancy. So, is vaccination a feasible option to control the disease? This article discusses some of these issues and reports on the progress towards a vaccine for neosporosis.

Redescription of Neospora caninum and its differentiation from related coccidia

Neospora caninum is a protozoan parasite of animals, which before 1984 was misidentified as Toxoplasma gondii. Infection by this parasite is a major cause of abortion in cattle and causes paralysis in dogs. Since the original description of N. caninum in 1988, considerable progress has been made in the understanding of its life cycle, biology, genetics and diagnosis. In this article, the authors redescribe the parasite, distinguish it from related coccidia, and provide accession numbers to its type specimens deposited in museums.

Neospora caninum in persistently infected, pregnant cows: spontaneous transplacental infection is associated with an acute increase in maternal antibody

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.

Immunization of Cattle with Live Tachyzoites of Neospora caninum Confers Protection against Fetal Death

ABSTRACT Neospora caninum is an obligate intracellular protozoan parasite that causes abortion in cattle. It is normally found as a latent infection controlled by a T-helper-cell type 1 response involving CD4+ cytotoxic T cells and gamma interferon. Cattle may be infected by two different routes: transplacentally as a result of activation of the latent infection in the mother causing congenital infection or abortion and by ingestion of oocysts, which, if it occurs during gestation, can also result in abortion. Here, for the first time, we establish proof that live vaccination protects against fetal death, whereas immunization using whole-tachyzoite lysate in different adjuvants fails to protect against fetal death. Strong antibody responses were induced in all the vaccinated groups, and the quality and magnitude of these responses were similar in the live- and the lysate-vaccinated groups. In contrast, only the group immunized with live tachyzoites had strong cellular and gamma interferon responses prior to challenge, and these responses correlated with protection against fetopathy. These results suggest that a cellular immune response may be important in the mechanisms involved in protection against N. caninum-associated abortions.

The Fasciola hepatica genome: gene duplication and polymorphism reveals adaptation to the host environment and the capacity for rapid evolution

BackgroundThe liver fluke Fasciola hepatica is a major pathogen of livestock worldwide, causing huge economic losses to agriculture, as well as 2.4 million human infections annually.ResultsHere we provide a draft genome for F. hepatica, which we find to be among the largest known pathogen genomes at 1.3 Gb. This size cannot be explained by genome duplication or expansion of a single repeat element, and remains a paradox given the burden it may impose on egg production necessary to transmit infection. Despite the potential for inbreeding by facultative self-fertilisation, substantial levels of polymorphism were found, which highlights the evolutionary potential for rapid adaptation to changes in host availability, climate change or to drug or vaccine interventions. Non-synonymous polymorphisms were elevated in genes shared with parasitic taxa, which may be particularly relevant for the ability of the parasite to adapt to a broad range of definitive mammalian and intermediate molluscan hosts. Large-scale transcriptional changes, particularly within expanded protease and tubulin families, were found as the parasite migrated from the gut, across the peritoneum and through the liver to mature in the bile ducts. We identify novel members of anti-oxidant and detoxification pathways and defined their differential expression through infection, which may explain the stage-specific efficacy of different anthelmintic drugs.ConclusionsThe genome analysis described here provides new insights into the evolution of this important pathogen, its adaptation to the host environment and external selection pressures. This analysis also provides a platform for research into novel drugs and vaccines.

Diagnosis and seroepidemiology of Neospora caninum-associated bovine abortion.

A round table was conducted at the VIIIth International Coccidiosis Conference on Neospora diagnosis with particular emphasis on strategies to diagnose bovine abortion. The strength and weakness of different assays for Neospora caninum infection and whether these methods have resulted in the overdiagnosis of neosporosis was discussed. It was evident that each diagnostic method, namely histology, immunohistochemistry, molecular detection and serological assays were, under certain circumstances, valuable in assessing the role N. caninum in abortion. Histological, immunohistochemical and molecular detection assays are of outstanding importance for the examination of tissues of aborted foetuses. While histology and immunohistochemistry allow direct assessment of pathomorphological changes caused by infection, molecular detection assays such as PCR are superior because of higher sensitivity and specificity in identifying N. caninum in foetal tissues. Serological tests, such as ELISA, are useful in determining whether an animal has been infected with N. caninum. Seroepidemiological approaches allow one to assess an abortion problem at a herd level and when used in conjunction with certain statistical methods are able to confirm a suspected N. caninum-associated abortion.

Fasciola hepatica is associated with the failure to detect bovine tuberculosis in dairy cattle

Bovine tuberculosis (BTB) is a significant and intractable disease of cattle caused by Mycobacterium bovis. In the UK, despite an aggressive eradication programme, the prevalence of BTB is increasing with an unexplained, exponential rise in cases year on year. Here we show in a study involving 3026 dairy herds in England and Wales that there is a significant negative association between exposure to the common, ubiquitous helminth parasite, Fasciola hepatica and diagnosis of BTB. The magnitude of the single intradermal comparative cervical tuberculin test used to diagnose BTB is reduced in cattle experimentally co-infected with M. bovis and F. hepatica. We estimate an under-ascertainment rate of about one-third (95% Confidence Intervals 27-38%) among our study farms, in the hypothetical situation of no exposure to F. hepatica. This finding may in part explain the continuing spread of BTB and the failure of the current eradication programme in the UK.

Emergence of fasciolosis in cattle in East Anglia

Liver fluke (Fasciola hepatica) infection caused weight loss, diarrhoea, decreased milk yield and occasionally death in cattle in East Anglia during the winters of 2001 to 2003. The condition had previously been limited mainly to stock imported into this part of Britain from endemically infected areas. In composite faecal samples collected by 16 farm animal veterinary practices in Norfolk, Suffolk and Essex, fluke eggs were found in 15 (28·8 per cent) of 52 previously unaffected suckler herds and 10 (16·7 per cent) of 60 dairy herds. Antibodies to F hepatica were detected by ELISA in 32 (53·3 per cent) of the bulk milk samples from these 60 dairy herds, including the 10 in which fluke eggs were found. The emergence of fasciolosis in East Anglia was attributed to recent higher summer rainfall, which favoured the intermediate snail host Lymnaea truncatula and the free-living stages of F hepatica, the increased influx of sheep from endemic fluke areas for seasonal grazing, and the wetter grazing conditions associated with the Environmentally Sensitive Area scheme.

Endogenous and exogenous transplacental transmission of Neospora caninum – how the route of transmission impacts on epidemiology and control of disease

Vertical transmission of the protozoan parasite, Neospora caninum is highly efficient and can take two forms - endogenous transplacental transmission resulting from activation of the quiescent bradyzoite stage during pregnancy or exogenous transplacental transmission resulting from ingestion of oocysts during pregnancy. Calves born carrying infection derived from either endogenous or exogenous transplacental transmission are capable of infecting their offspring when they start to breed. This review considers firstly the frequency with which exogenous and endogenous transmission occur, secondly the role of the immune response in controlling N. caninum infection and thirdly how the parasite persists in an immune-competent host and is re-activated during pregnancy.