Quantification,risk factors,and health impact of natural congenital infection with bovine viral diarrhea virus in dairy calves

OBJECTIVES: To estimate risk and identify risk factors for congenital infection with bovine viral diarrhea virus (BVDV) not resulting in persistent infection and examine effect of congenital infection on health of dairy calves. ANIMALS: 466 calves. PROCEDURES: Calves from 2 intensively managed drylot dairies with different vaccination programs and endemic BVDV infection were sampled before ingesting colostrum and tested with their dams for BVDV and BVDV serum-neutralizing antibodies. Records of treatments and death up to 10 months of age were obtained from calf ranch or dairy personnel. Risk factors for congenital infection, including dam parity and BVDV titer, were examined by use of logistic regression analysis. Effect of congenital infection on morbidity and mortality rates was examined by use of survival analysis methods. RESULTS: Fetal infection was identified in 10.1% of calves, of which 0.5% had persistent infection and 9.6% had congenital infection. Although dependent on herd, congenital infection was associated with high BVDV type 2 titers in dams at calving and with multiparous dams. Calves with congenital infection had 2-fold higher risk of a severe illness, compared with calves without congenital infection. CONCLUSIONS AND CLINICAL RELEVANCE: The unexpectedly high proportion of apparently healthy calves found to be congenitally infected provided an estimate of the amount of fetal infection via exposure of dams and thus virus transmission in the herds. Findings indicate that congenital infection with BVDV may have a negative impact on calf health, with subsequent impact on herd health.     

Torque teno virus infection in the pig and its potential role as a model of human infection

Torque teno viruses (TTVs), of the genus Anellovirus, are single-stranded circular DNA viruses that infect many vertebrate species. Although viruses of this type have quite a stable genome, they exhibit low nucleotide homology. Torque teno virus infection has not been consistently linked to specific diseases, although there is epidemiological evidence of an association with disease in humans. The recent recognition of naturally occurring TTV infection in swine and its epidemiological resemblance to human TTV raises the possibility of using the pig as a model to study human TTV infection. Such an approach will require the development of novel investigative tools to study the epidemiology, transmission, immune responses and potential pathogenesis of TTV infection. The present review summarises research on animal TTV infection, focussing in particular on TTV infection in the pig, and considers how a porcine experimental infection model might assist in the study of human TTV infection.     

The effect of Plasmodium gallinaceum on a challenge infection with Ascaridia galli in chickens

The effect of a primary infection with the haemoparasite Plasmodium gallinaceum on the establishment of a challenge infection with the nematode Ascaridia galli in chickens was studied. Four groups were infected as follows. Group 1: inoculated intravenously with 10(6) P. gallinaceum-infected erythrocytes on day 0; group 2: orally infected with 500 embryonated A. galli eggs on day 10; group 3: infected with P. gallinaceum on day 0 and A. galli on day 10; and group 3: non-infected control birds. The results of this investigation demonstrates that a primary infection with P. gallinaceum in chickens alters the course of a subsequent infection with A. galli. Thus, an antagonistic effect was seen in which the malaria infection caused a significant reduction on the establishment of the nematode in concurrently infected animals.     

Protection against and establishment of Dictyocaulus viviparus following primary infection at different dose levels

In two experiments, calves were primary infected with 1 of 12 (Experiment 1) or 6 (Experiment 2) different dose levels of Dictyocaulus viviparus infective larvae (L3), ranging from 5 to 2000 L3. To study the level of protection induced by the primary infection a challenge infection with 2000 L3 was given on day 10 (Experiment 1) or day 35 (Experiment 2). In both experiments, challenge control calves were included. Eleven days later, the challenge calves were necropsied for worm counts. Results were compared with predictions from a simulation model. Establishment of the primary infection was dose independent, lying on average in the range of 20-30%. The ratio female:male worms in the counts from the primary or from the challenge infection was consistently close to 1:1 irrespective of primary infection dose level or protection having developed in some of the calves. Level of early protection (10 days after a primary infection-Experiment 1) against establishment of the challenge infection depended significantly on primary infection dose level (P<0.01). At 10 days, after a primary infection, low dose levels did not result in protection against a challenge infection. In contrast, similarly low dose levels did result in partial protection, 35 days after the primary infection. Results confirmed that our provisional simulation model satisfactorily predicts primary infection outcomes, but that it does not accurately predict levels of protection and immunity against re-infections.     

Transmission studies on Trichinella species isolated from Crocodylus niloticus and efficacy of fenbendazole and levamisole against muscle L1 stages in Balb C mice

Forty-four Balb C mice, aged 18 weeks were infected with crocodile (Crocodylus niloticus)-derived Trichinella species. Of the infected mice, 32 were randomly divided into two groups each containing equal numbers of males and females; levamisole treated group and fenbendazole treated group. Each group was randomly subdivided into two subgroups as follows: levamisole group (subgroup 1: treated with levamisole on day 35 post infection, and subgroup 2: treated with levamisole on days 35 and 42 post infection) and fenbendazole group (subgroup 1: treated with fenbendazole on day 35 post infection and subgroup 2: treated with fenbendazole on days 35 and 42 post infection). The first subgroups treated on day 35 post infection were slaughtered on day 42 post infection and the second subgroups were treated on day 35 and day 42 post infection and slaughtered on day 49 post infection. Two female mice were infected a day after mating and were slaughtered together with the offspring on day 64 post-infection. Ten infected control mice were given 1 ml distilled water orally as placebo, and five of these were slaughtered on day 42 post infection. The results showed that the mean reproductive capacity index of this strain (RCI) in Balb C mice was 110. There was a significant reduction (P < 0.01) in larval counts in the single treatment groups (day 35) and in the double treatment groups (days 35 and 42) for both anthelmintics when compared the number of parasites in the control groups. After a single treatment, levamisole reduced the infection by 79.9% and fenbendazole by 76.7%. Following double treatments, levamisole reduced the infection by 95.5% and fenbendazole by 99.1%.There was evidence that the infected pregnant mice transmitted the parasite to their offspring. It is not certain whether the parasite was transmitted congenitally or transmammary Alternative ways of controlling the parasite in crocodile farms in Zimbabwe are discussed.     

The influence of relative resistance and urea-supplementation on deliberate infection with Teladorsagia circumcincta during winter

The consequences for lambs of infection over the winter with Teladorsagia circumcincta were quantified by deliberate, trickle infection of selected animals at 7 months of age. Infected and control uninfected animals were each allocated into four groups, relatively resistant animals on a normal diet, relatively resistant animals on an isocaloric diet supplemented with urea, and relatively susceptible animals on the same two diets. Resistance and susceptibility was assessed by faecal egg counts following natural infection during the summer preceding the deliberate infection. During the deliberate infection egg counts remained low and most parasites recovered at necropsy were inhibited larvae. Nonetheless, infection reduced weight gain, decreased albumin and fructosamine concentrations and provoked a noticeable pepsinogen and eosinophil response. As most larvae were inhibited these responses may have been largely a consequence of immuno-inflammatory responses in the host rather than the direct action of parasites themselves. Relatively resistant animals on the supplemented diet allowed fewer larvae to establish and had higher fructosamine concentrations, higher albumin concentrations and decreased pepsinogen responses. Therefore, a combination of relatively resistant sheep and nutritional supplementation appears most efficient at controlling infection.     

Investigating clustering in interval-censored udder quarter infection times in dairy cows using a gamma frailty model

Udder infections in dairy cows are observed at udder quarter level. Therefore, the best strategy to study infection dynamics of particular bacteria causing mastitis is to follow up and model individual udder quarter infection times. Udder quarter infection times, however, are not independent as they are clustered within a cow and herds. Another challenge in modelling infection times is that the exact infection time is unknown; it is only known that the infection has taken place in the interval between the last negative and the first positive sample. We applied a technique based on the gamma frailty model which handles the clustering and interval censoring simultaneously. Parameter estimates can be obtained analytically and their variance is obtained by the inverse of the hessian matrix. The proposed technique was applied to udder quarter infection times for Corynebacterium bovis, Staphylococcus aureus and Streptococcus uberis. Multiparous cows were more likely to get infected earlier in lactation with C. bovis or S. uberis than primiparous cows. The times to infection of all three bacteria were highly clustered at cow level and the results of a stratified model on a subset of herds suggested a high clustering on herd level for C. bovis and S. uberis.     

Evaluation of an ELISA to assess the intensity of Fasciola hepatica infection in cattle

An elisa with a diagnostic sensitivity of 98 per cent and specificity of 96 per cent was evaluated as a means of assessing the intensity of Fasciola hepatica infection in cattle. A total of 294 blood samples were collected from infected cattle at a local abattoir, and the level of infection in each animal was assessed on the basis of the extent of liver pathology and the presence of flukes; 120 blood samples were also collected from uninfected cattle kept on a farm known to be free of F hepatica. The results indicated that there was a significant correlation (P<0.001) between the elisa values and the intensity of infection. Values between 15 and 28 per cent of a positive control sample indicated a low intensity of infection, values between 28 and 50 per cent indicated a medium intensity of infection and values above 50 per cent indicated a high intensity of infection.     

Immunological characteristics of experimental murine infection with Leishmania (Leishmania) amazonensis

The murine models of Leishmania infection are well-studied and suitable models for studying this disease, which, despite its incidence of nearly 2 million new cases worldwide per year and its prevalence of 12 million cases, has been a somewhat neglected disease. Data obtained using such models are important for a better understanding of the disease in humans due to similarities in physiology and the advantage provided by the uniform infection profile within each mouse strain. In this review, we focus on studies of experimental murine infection with Leishmania (Leishmania) amazonensis, a species that has been associated with infections exhibiting various clinical features in humans. Mainly, we point out and discuss reports on: the effects of variations of the inoculum (such as strain, site, and size) in the establishment and development of the infection; characteristics of the infection in distinct mouse strains; and, the effects and subversions of the infection on components of the host innate and adaptive immune responses. The results obtained in these studies show that L. (L.) amazonensis infection in mice presents some unique features and immunoregulatory mechanisms, making it an interesting model for obtaining further knowledge of potential drugs targets and immunotherapy in Leishmania infection.     

The specificity of the fluorescent antibody test using the sera of rabbits inoculated with strains of myocobacteria.

Sera from experimentally infected rabbits were used to test the specificity of the fluorescent antibody test. It was possible using mono-specific sera to differentiate antigenically Mycobacterium phlei, M fortuitum, M smegmatis, M avium, M intracellulare, M bovis (BCG) and M johnei. The cross-reactivity within the M avium and M intracellulare group was such that one antigen from these groups would detect infection within that group and exclude M johnei infection. The M phlei growth factor independent strain M johnei 316F was shown to be antigenically distinct from a M phlei dependent strain 9N96. There was loss of specificity when M avium infection was superimposed on a previous M johnei infection and when M johnei infection was superimposed on M avium infection.     

The status of Mycobacterium bovis infection in UK wild mammals: a review

Bovine tuberculosis caused by Mycobacterium bovis is a zoonotic infection with a wide range of mammalian hosts. In parts of the UK M. bovis infection in cattle is a persistent problem. The European badger (Meles meles) is implicated in the transmission of M. bovis to cattle, and is widely believed to constitute the most important reservoir of infection in UK wildlife. However, few studies have been carried out on the status of M. bovis infection in other UK mammals. In this review we present information on the incidence and pathology of M. bovis infection in UK wild mammals from both published and previously unpublished sources. Although the evidence does not support the existence of a significant self-maintaining reservoir of infection in any wild mammal other than the badger, there is a clear lack of sufficient data to rule out the involvement of other species. In the light of this and the dynamic nature of epidemiological patterns, further surveillance for M. bovis infection in UK wild mammals, using modern methods of diagnosis, is essential.     

The transmission of mixed Trypanosoma brucei brucei/T. congolense infections by tsetse (Glossina morsitans morsitans)

Laboratory experiments and field observations clearly show that tsetse flies can be carriers of mixed trypanosome infections. Question remains how easy it is for the tsetse fly to acquire such a mixed infection during the first bloodmeal. This is of particular importance in the epidemiology of Trypanosoma brucei s.l., often a cryptic infection and difficult to transmit to non-teneral tsetse flies. To determine the transmission rate of T. brucei as part of a mixed infection, teneral Glossina morsitans morsitans were fed once on cattle with a mixed (Trypanosoma brucei brucei/Trypanosoma congolense) or single (T. brucei) infection. Of the 140 flies fed on animals with a mixed infection and examined 30 days later, 4 had a metacylic T. brucei infection, 29 a T. congolense infection and 13 a mixed T. brucei/T. congolense infection. There was no significant difference between the transmission rate of T. brucei as a single or as part of a mixed infection. The high proportion of mixed T.b. brucei/T. congolense infections was explained best by a model implying that if a fly is refractory to T. congolense, it is also refractory to T.b. brucei and vice versa. Hence, results suggest that the transmission of T.b. brucei is affected mainly by the vectorial capacity of flies and not by concurrent trypanosome infections in the host.     

The behavior of the Q-fever agent, Coxiella burnetii, in birds. 3. Experimental infection of quail]

After simultaneous aerogenic and alimentary infection of quail by intra-nasal inoculation of a suspension of C. burnetii, the agent was reisolated 6 h after infection from lung and gut, from the 3rd day on from the spleen, at the 8th and 10th day from blood, and from the 8th day on from liver and kidney. C.burnetii was found in various organs up to 21 days after infection. In the majority of birds agglutinating antibodies could be demonstrated from the 18th day up to termination of the experiment 66 days after infection. On the basis of these results the course of a C. burnetii infection in birds is discussed.     

Experimental infection of domestic pigeons with pigeon circovirus

Pigeon circovirus (PiCV) infection and young pigeon disease syndrome (YPDS), associated with high morbidity and mortality, have been recognized in young racing pigeons from large portions of Central Europe. There exist a number of data indicating that YPDS is a consequence of PiCV infection and subsequent immunosuppression. In order to prove PiCV to be one of the crucial factors of YPDS, an experimental infection with PiCV was performed under controlled conditions. Twenty-four domestic pigeons (Columba livia forma domestica) were divided into two groups with 12 pigeons each; an infection group and a control group. All birds were between their fourth to eighth week of life. Pigeons in the infection group were infected both intramuscularly and orally with PiCV purified from naturally infected birds, while pigeons in the control group received a placebo. To test a possible influence of the PiCV infection on the immune system, the animals in both groups were vaccinated simultaneously, on the same day, against PMV-1 (Lasovac plus, IDT, Dessau-Tornau, Germany). Weekly virologic testing showed a viraemic period, and excretion of the infection virus, in pigeons in the infection group. Replication of PiCV could be proved on the basis of histologic findings of multiglobular inclusion bodies, mainly observed in macrophages of the bursa of Fabricius. A PiCV, genetically distinct from the experimental virus, was detected in the control group by polymerase chain reaction (PCR) testing, but any histologic findings comparable to the infection group were absent. None of the pigeons revealed clinical signs of illness, or hints that immunosuppression had occurred, regardless of their group. The absence of stressful conditions, considered as a trigger for the development of YPDS, may be responsible for the failure of disease reproduction in our infection model.     

Segregation of natural and experimental gastrointestinal nematode infection in F2 progeny of susceptible Suffolk and resistant Gulf Coast Native sheep and its usefulness in assessment of genetic variation

Gastrointestinal nematode parasitism is a concern to small ruminants worldwide. Productivity has been compromised because such nematodes, particularly Haemonchus contortus, have developed resistance to available anthelmintics. Some sheep breeds and lines within breeds are relatively resistant to infection, a trait that may be useful for developing control strategies. Suffolk sheep, which are susceptible to infection, were crossed with Gulf Coast Native sheep, which are more resistant to infection, to produce F1 progeny. F1 rams were bred to F1 ewes which produced 227 F2 offspring. These F2 offspring were evaluated for variability in infection levels, based on fecal egg count (FEC) and blood packed cell volume (PCV), under two natural infection conditions (one at weaning and another after a summer grazing period) and one experimental infection. The range of both FEC and PCV was large for all three infection periods with annual variation. Overall, the range for the three infection periods, respectively, were 167-149,933, 0-31,400 and 17-114,667 eggs per gram (EPG) of feces and 8.7-37.0%, 7.3-33.0% and 8.3-36.0%. This segregation of infection is what would be expected of F(2) progeny from susceptible and resistant parent breeds. Heritabilities of FEC and PCV for the three infection periods, respectively, were 0.15, 0.29 and 0.12, and 0.11, 0.22 and 0.12. Based on segregation of infection, larger heritabilities and maternal environment effects that declined after weaning, the summer natural infection was probably the best model for assessing genetic variation.     

Evaluation of immunological, parasitological and molecular methods for the diagnosis of Schistosoma mansoni infection before and after chemotherapy treatment with praziquantel in experimentally infected Nectomys squamipes

In low endemicity areas of schistosomiasis, the recommended diagnostic method of coprological examination results in an underestimation of infection cases. Alternative diagnostic methods have been developed, such as immunodiagnostic and molecular techniques. In this study we evaluated three methods used in the diagnosis of Schistosoma mansoni infection: parasitological (Kato-Katz), immunological (ELISA) and molecular (real time PCR), and also investigated the sensitivity of each technique in the cure determination after treatment with praziquantel using the water rat Nectomys squamipes, a natural reservoir for S. mansoni, as an experimental model. Two infection laboratory experiments were carried out. The first experiment aimed to observe the evolution of the immunological response in the first moments after infection and in the first months after treatment. The second experiment aimed to compare the efficacy of the three diagnostic techniques after infection and after treatment over a more extended time period. In the first experiment, 44% of the infected animals showed IgG reactivity after two weeks of infection, and 94% were positive based on serology 30 days after infection. The serological IgG titers increased just after infection but decreased gradually after treatment. In the second experiment, 89% of the animals showed positive IgG titers 22 days after infection. Only 68% of the animals showed positive results on the coproscopic diagnostic analysis and 79% did so by qPCR, 50 days after infection. Treated animals showed negative results on coproscopy one month after treatment but remained positive by serology even 12 months after treatment, although showing a decline in immunologic reaction after treatment. By qPCR analysis, all animals showed negative results three months after treatment, except for one animal. The parasitosis can be detected by coproscopy only six weeks after infection, and by serology 14 days after infection. The qPCR was a better diagnostic method for confirming the infection cure of S. mansoni. In early infection, this method was less efficient than serology but was slightly more efficient than the Kato-Katz method. We suggest that the methods should be used in low endemic areas as follows: serology should be used in the initial diagnosis in a population with potential positive cases; subsequently, coproscopy should be used in IgG positive cases to confirm the current infection; and qPCR should be used to evaluate the infection cure after treatment and is also a very valuable tool when there are cases showing positive IgG and negative coproscopy.     

The effect of T. vivax infection in West African Dwarf goats on energy and nitrogen metabolism

Summary

To investigate how T. vivax affects metabolism in dwarf goats, nine wethers (infection group) given alfalfa pellets ad libitum were infected intravenously and food intake was recorded up to 49 days after infection in the infection group and in the control group (n=9). Controls received the same diet, ad libitum before infection and in restricted amounts after infection in order to obtain similar intakes in the two groups. Digestible organic matter intake (DOMI) and nitrogen balance (NB) were determined during four balance trials. All animals were bled regularly to measure parasitaemia, packed cell volume (PCV) and a number of serum metabolites.

All infected animals showed symptoms typical for T. vivax infection as judged by parasitaemia, PCV and rectal temperature. Infection had a non‐uniform negative effect on food intake. Compared with controls at equal DOMI, NB was lower in infected animals, the difference being significant 4 weeks after infection. This was caused by a gradual increase in NB at equal DOMI of the control group. The NB of the ad libitum fed infected animals 2 and 4 weeks after infection was comparable to values normally found in healthy ad libitum fed dwarf goats with an equal DOMI.

NEFA values in serum were significantly elevated after infection. Except for two infected animals with an extremely low food intake towards the end of the experiment, no rise in serum ketone bodies was evident. After infection, serum protein increased, differences with controls being significant 4 and 7 weeks after infection.

It is concluded that T. vivax infection results in a decrease in energy intake and a decrease in NB up to at least 4 weeks after infection. At equal DOMI, NB of infected animals was not lower than expected for ad libitum fed healthy animals but was lower than in healthy controls on a restricted diet, probably as a result of a decrease in maintenance requirements of the latter. The data on NB and serum NEFA concentrations suggest that non‐protein energy sources are used to supply the increased energy demand as a result of infection.     

The development of Akabane virus-induced congenital abnormalities in cattle

A prospective study of the incidence and severity of congenital deformities of calves, attributable to maternal infection by Akabane virus, was carried out on a population of 174 susceptible animals that were between one and nine months pregnant at the time of infection. The study was carried out in the Hunter Valley of New South Wales during 1983, after an epidemic of Akabane virus infection in late February to early March 1983. The incidence of virus-induced abnormalities in calves and fetuses was 17.8 per cent (31/174). The highest incidence of abnormalities occurred during the third and sixth months of gestation (27 to 29 per cent). The earliest abnormality was observed after infection at 76 days of gestation, and the last after infection at 249 days. The development of the pathological entities of hydranencephaly/porencephaly and arthrogryposis were found to be quite distinct. Cases of hydranencephaly and porencephaly developed after infection between 76 and 104 days of gestation whereas arthrogryposis developed after infection between 103 and 174 days of infection. It was concluded that the type of congenital deformity produced by maternal infection with Akabane virus was dependent on the stage of fetal development at the time of infection. The data suggest that the infection was transplacental and that fetuses of less than two months of age were protected from infection.     

The epidemiology of Dictyocaulus filaria in north east England.

The seasonal pattern of Dictyocaulus filaria infection in four flocks of sheep under field conditions was studied by faecal examination for larvae. The prevalence of infection in lambs was low in spring and summer but increased in late autumn or winter, then fell again to a low level by May. However, most lambs became infected at some time during their first year of life. In ewes the prevalence of infection was generally low, but rose during winter and spring. Seasonal pattern and intensity of infection were influenced by weather conditions and the persistence of infection from the previous year, moist summer conditions giving rise to a higher level of infection in autumn and winter than a dry summer. The source of infection may be the ewes or yearlings, or infective larvae surviving over the winter on pasture. Autoinfection occurred, some lambs becoming infected with at least three generations of the parasite, but at the levels of infection recorded clinical disease was rare.     

Resistance of leopard tortoises and helmeted guineafowl to Cowdria ruminantium infection (heartwater).

Experimental infection trials were conducted to investigate susceptibility of leopard tortoises (Geochelone pardalis) and helmeted guineafowl (Numida meleagris) to infection with Cowdria ruminantium, the causative agent of heartwater, a tickborne disease of domestic and wild ruminants. Ten guineafowl were inoculated intravenously with a virulent dose of C. ruminantium derived from bovine endothelial cell cultures, and four leopard tortoises were exposed to C. ruminantium infection by the feeding of infected Amblyomma hebraeum ticks. Uninfected A. hebraeum ticks (on both tortoises and guineafowl) and Amblyomma marmoreum ticks (on tortoises only) were fed on the animals during weeks 2 and 3 post-exposure in an attempt to detect infection. These ticks were analyzed for C. ruminantium infection by xenodiagnosis and with the C. ruminantium-specific pCS20 polymerase chain reaction (PCR) assay. Attempts to detect infection in ticks fed on either species were negative by both tests. These results suggest that leopard tortoises and helmeted guineafowl are refractory to C. ruminantium infection and, therefore, are unlikely to be capable of introducing heartwater directly into new areas. However, leopard tortoises are efficient hosts of A. marmoreum and A. hebraeum and are likely to be important epidemiologically in the transport and maintenance of these tick vector species.