Persistent Infection In Cattle Research Articles

Effect of bovine viral diarrhea virus in the feedlot.

It could be argued that bovine viral diarrhea virus (BVDV) is one of the most economically significant infectious pathogens of feedlot cattle. Although the direct economic losses caused by this virus have not been well quantified, the role it plays as an immunosuppressive agent and as a potentiator for other diseases, most notably bovine respiratory disease, have been well documented. It is also a difficult disease for the feedlot veterinarian to control effectively. Individual cattle persistently infected with BVDV often serve as the source of infectious virus within a group of feedlot cattle, and the ultimate responsibility for preventing persistent infections in cattle rests with the cow-calf producer and not with the feedlot owner. The enormous impact of the virus on the livestock industry has led the Academy of Veterinary Consultants to draft a position statement that resolves that the beef and dairy industries adopt measures to control and target eventual eradication of BVDV from North America.

Review of the relationship between persistent infection of cattle with bovine viral diarrhea virus and feedlot morbidity and gain

Bovine viral diarrhoea is an infectious viral disease of cattle. Persistently infected cattle result from in-utero infection of calves with the bovine viral diarrhoea virus during critical stages of gestation, and affected calves become lifetime carriers of the virus. Cattle persistently infected with the virus can be a source of infection to healthy pen mates in a feedlot setting. The feedlot industry is a cost-driven, low-margin business, and cattle need to perform efficiently to be profitable. Morbidity can have a significant impact on profitability. This paper reviews the relationship between calves persistently infected with bovine viral diarrhoea virus and the health and performance of feedlot cattle at the pen level.

Introduction to the food safety concerns of verotoxin-producing Escherichia coli.

Verotoxin-producing Escherichia coli (VTEC) have emerged in the past two decades as food-borne pathogens that can cause major outbreaks of human illnesses worldwide. The number of outbreaks has increased in recent years due to changes in food production and processing systems, eating habits, microbial adaptation, and methods of VTEC transmission. The human illnesses range from mild diarrhea to hemolytic uremic syndrome (HUS) that can lead to death. The VTEC outbreaks have been attributed to O157:H7 and non-O157:H7 serotypes of E. coli. These E. coli serotypes include motile (e.g., O26:H11 and O104:H21) and nonmotile (e.g., O111:H-, O145:H-, and O157:H-) strains. In the United States, E. coli O157:H7 has been the major cause of VTEC outbreaks. Worldwide, however, non-O157:H7 VTEC (e.g., members of the O26, O103, O111, O118, O145, and O166 serogroups) have caused approximately 30% of the HUS cases in the past decade. Because large numbers of the VTEC outbreaks have been attributed to consumption of ruminant products (e.g., ground beef), cattle and sheep are considered reservoirs of these food-borne pathogens. Because of the food safety concern of VTEC, a global perspective on this problem is addressed (Exp Biol Med Vol. 228, No. 4). The first objective was to evaluate the known non-O157:H7 VTEC strains and the limitations associated with their detection and characterization. The second objective was to identify the VTEC serotypes associated with outbreaks of human illnesses and to provide critical evaluation of their virulence. The third objective was to determine the rumen effect on survival of E. coli O157:H7 as a VTEC model. The fourth objective was to explore the role of intimins in promoting attaching and effacing lesions in humans. Finally, the ability of VTEC to cause persistent infections in cattle was evaluated.

Verotoxin 1 from Escherichia coli affects Gb3/CD77+ bovine lymphocytes independent of interleukin-2, tumor necrosis factor-alpha, and interferon-alpha.

Verotoxin (VT)-induced immunomodulation has been implicated in the ability of VT-producing Escherichia coli (VTEC) to cause persistent infections in cattle. VT1, also referred to as Shiga toxin 1, is a potent cytotoxin that modulates cytokine secretions and functions. This prompted the current investigation to examine whether the inhibiting effect of VT1 on bovine lymphocytes correlates with the expression of the cellular VT1 receptor Gb3/CD77 or is mediated instead via perturbation of cytokine secretion. Using blood mononuclear cells stimulated by mitogens as a model, VT1 significantly blocked lymphoblast transformation and proliferation in the BoCD8+ T cell and BoCD21+ B cell population. In contrast, VT1 dramatically reduced the number of viable Gb3/CD77+ blast cells within all subpopulations identified (BoCD2+, BoCD4+, BoCD8+, WC1+ [i.e., gammadelta T cells] BoCD21+, and BoCD25+). Similar effects of VT1 were observed when the culture medium was supplemented with selected cytokines: tumor necrosis factor-alpha-sensitizing endothelial cells against VT1, interferon-alpha (IFN-alpha) as bovine IFN-alpha receptors are partially homologous to the B-subunit of VT1, and interleukin-2 that is critical for lymphocyte proliferation in vitro. The addition of these cytokines was neither able to mimic nor to overcome the effects of VT1. Therefore, it is concluded that VT1 directly acts on bovine lymphocytes rather than inducing a cytokine-mediated effect. VT1 considerably affects all main bovine lymphocyte subpopulations, implicating that the immune system is a predominant target for VT1 in cattle.

Isolation of parapoxvirus from a cow treated with interferon-γ

A virus was isolated from peripheral blood leukocytes of a cow which was kept in an isolated pen after it was injected with recombinant bovine interferon-γ. The virus was identified as a member of genus Parapoxvirus in the family Poxviridae on the basis of electron microscopic observations and serological tests. Parapoxvirus has seldom been isolated other than from papular lesions, the characteristic sign of parapoxvirus infection. This is the first report of parapoxvirus isolation from the peripheral blood of a cow without any clinical signs. These results show that parapoxviruses are capable of causing persistent infection in cattle without clinical signs and can be activated by stress factors that induce modification of immune reactions. Relationships between the isolated virus and other parapoxviruses isolated previously from cattle in Japan were investigated and discussed.

Clonality of Campylobacter sputorum bv. paraureolyticus determined by macrorestriction profiling and biotyping, and evidence for long-term persistent infection in cattle.

Eighteen strains of Campylobacter sputorum bv. paraureolyticus (isolated over a 12-month period from seven dairy cows contained in a single herd) were examined by resistotyping, and macrorestriction profiling using pulsed field gel electrophoresis (PFGE). The resistotypes of these strains were identical, although repeat testing indicated resistance to metronidazole was not a reliable trait for typing purposes. Five SmaI-derived genotypes were identified among the 18 strains. In 5 of 7 cows, isolates obtained from the same animal, but from different time periods, were genotypically indistinguishable, indicating persistence of infection. Macrorestriction profiles of 5 strains representing the 5 SmaI genotypes and 8 other strains of C. sputorum from various sources, were prepared using 4 endonucleases (SmaI, SalI, BamHI and KpnI). The only other strain of C. sputorum bv. paraureolyticus examined (a Canadian isolate from human faeces), was found to have a SmaI macrorestriction profile identical with one of the five clones isolated from the cattle. Moreover, SalI and BamHI profiles of all bv. paraureolyticus strains were similar, while digestion with KpnI was not observed. By contrast, the seven strains of C. sputorum bv. sputorum yielded various macrorestriction profiles with all the enzymes used, and features distinguishing the two biovars studied could be identified. This study indicates that C. sputorum can persist in cattle for at least 12 months and exhibits a clonal population genetic structure.

Population dynamics of Theileria sergenti in persistently infected cattle and vector ticks analysed by a polymerase chain reaction.

Theileria sergenti Shintoku stock consists of 2 parasite populations bearing 2 allelic forms of p33/32, an immunodominant piroplasm surface protein. Parasite population changes during parasite passages among cattle and tick vectors, and during persistent infection in individual calves were analysed by using allele-specific polymerase chain reaction (PCR). The parasite DNAs were prepared from piroplasms from calves which had been infected with Shintoku stock by inoculation of sporozoite stabilates or parasitized erythrocytes, and from sporozoite stabilates which had been prepared from Shintoku stock-infected ticks. Changes in a dominant parasite population were demonstrated during transmission from calves to vector ticks and from infected ticks to calves. Parasite population changes were also apparent during persistent infection in cattle over several months, and this change is thought to occur under host immune pressure. The results of this study indicate that expression of diverse forms of p33/32 may play a role in parasite persistence within mammalian hosts and its transmission from tick vector.

Genetic variation of foot-and-mouth disease virus during persistent infection in cattle

Genetic variation of foot-and-mouth disease virus O 1 Campos has been analyzed in consecutive isolates recovered over a one- or two-year period from four cattle with experimental persistent infection. Comparisons of RNase T 1 two-dimensional maps and nucleotide sequences of the VP 1-coding region revealed a continual, although irregular, increase in the fixation of mutations as the infection progressed. Most changes were not conserved in consecutive isolates. These results, together with the substantial rates of genomic variation observed between some pairs of strains recovered at close time periods, suggested the coexistence of heterogeneous populations in which variants evolve independently from each other, and predominate at irregular time intervals. Furthermore, non-related patterns of variation were observed in the four animals. Similarly, genetic diversity of representative strains from major serotype O outbreaks in endemic disease regions of southeastern Brazil and central eastern Argentina which occurred between 1958 and 1983, suggested that outbreak strains are also likely to represent fluctuations of heterogeneous populations which evolve independently from each other. The possible role of persistent infections in the introduction of variant populations in the field is discussed.

Persistent Infection of Cattle with BVD Virus

The results of laboratory and field investigations indicate a link between persistent infection with BYD virus and mucosal disease. Both noncytopathic and cytopathic BYD viruses have been isolated from field cases of mucosal disease and mucosal disease has been experimentally produced in cattle persistently infected with noncytopathic BYD virus by superinfection with cytopathic BYD virus. The prevalence of persistent BYD virus infection is unknown but is probably high enough to be of concern. The persistently infected cow is a source of infection for other cattle, passes the persistent infection on to her offspring, and is at risk of developing mucosal disease.

Persistent Infection of Cattle with the Herpesvirus of Malignant Catarrhal Fever and Observations on the Pathogenesis of the Disease

A case of persistent MCF virus infection is described. A steer was inoculated with attenuated virus and apparently withstood challenge with virulent MCF virus. Five months later it developed a viraemia which persisted for four weeks and the animal died after only one day’s fever. Post-mortem and histological studies showed extensive ulcerative, haemorrhagic enteritis and a necrotizing polyvasculitis with mononuclear leucocyte infiltration. Experimental studies have demonstrated viraemia to preceed fever in cases of acute MCF. The pathogenesis of MCF is discussed in the light of these findings and it is concluded that MCF might be an immune complex disease.