Space-time clustering of, and risk factors for, farmer-diagnosed winter dysentery in dairy cattle

We used two statistical techniques for space-time cluster analysis, the Knox and the Mantel regression methods, for an analysis of whether herd outbreaks of farmer-diagnosed winter dysentery during the winter of 1987-1988 were clustered in space and time more than would be expected by chance. Using the Knox method, there was significant space-time clustering of outbreaks of winter dysentery within a 30 day time and a 5.5 km radius. There was also significant space-time clustering by the Mantel regression method.     

Conclusions from the outbreak of foot-and-mouth disease in the government district of Hannover in 1987/1988

Kn?sel und Tiroke (1989) reported recently experiences derived from the control of FMD outbreaks in 1987/88 in Lower Saxony (FRG). On the basis of the described facts and in connection with the observations of the other outbreaks during the last 20 years in the FRG several conclusions were drawn: (1) The compulsory annual vaccination was not able to prevent these outbreaks. (2) Hence follows that very probable introductions of FMD from foreign countries cannot be prevented, especially since such infections were due to infected swill fed to pigs, and those strains were normally not related to the vaccine strains used. (3) Considering all circumstances of the recent outbreaks, it seems unrealistic to believe the primary infection was not due to the escape of virus from the neighboring vaccine plant. (4) The annual vaccination campaigns since 1970 against FMD were useless because most of the primary outbreaks of FMD since then can be traced to the production or the application of vaccines. (5) The legislative control measures are not sufficient to prevent secondary outbreaks. It was recommended to extend the quarantine areas as well as the radius of ring vaccination and to prolong the period of quarantine. (6) The regulation of tremendous losses of trade is obscure because camouflage of the origin of infections blocks the application of the principle of ultimate responsibility. Facit: Eradication of the disease and strict prevention of its introduction into Europe should be the principal strategy of FMD control for the future instead of imperfect protecting one species of the susceptible animal population.     

Genetic diversity of Anaplasma marginale strains from an outbreak of bovine anaplasmosis in an endemic area

Anaplasma marginale is a tick-borne pathogen of cattle that causes the disease bovine anaplasmosis worldwide. Major surface proteins (MSPs) are involved in host-pathogen and tick-pathogen interactions and have been used as markers for the genetic characterization of A. marginale strains. A. marginale genotypes are highly variable in endemic areas worldwide. The genetic composition of A. marginale strains during anaplasmosis outbreaks has been characterized in one study only which reported a single msp1alpha genotype in infected cattle. However, more information is required to characterize whether a single genotype is responsible for an anaplasmosis outbreak or whether multiple genotypes can cause disease in na?ve cattle within a single herd in endemic areas. The aim of this study was to characterize the genetic diversity of A. marginale strains from an outbreak of bovine anaplasmosis in the State of Tamaulipas, Mexico. A. marginale genotypes were characterized at the molecular level using msp4 and msp1alpha gene sequences. The results revealed that several A. marginale genotypes are present in cattle during acute anaplasmosis outbreaks, thus suggesting that mechanical transmission or stochastic biological transmission through equally efficient independent transmission events may explain A. marginale genotype frequency in a cattle herd during acute bovine anaplasmosis outbreaks in endemic areas. The results reported herein corroborated the genetic heterogeneity of A. marginale strains in endemic regions worldwide. The development and implementation of anaplasmosis control measures is dependent upon understanding the epidemiology of A. marginale in endemic regions, including the characterization of the genetic diversity of strains that produce outbreaks of bovine anaplasmosis.     

Control of a foot-and-mouth disease epidemic in Argentina

A major epidemic of foot-and-mouth disease affected Argentina during 2001. The epidemic was controlled by mass-vaccination of the national herd and movement restrictions. The median herd disease reproduction ratio (R_H) decreased significantly from 2.4 (before the epidemic was officially recognized) to 1.2 during the mass-vaccination campaign and <1 following the mass-vaccination campaign. The largest distance between two outbreaks was similar during (1905 km) and after (1890 km) the mass-vaccination. However, after mass-vaccination was completed, the proportion of herd outbreaks clustered decreased from 70.4% to 66.8%, respectively. Although a combination of vaccination and livestock-movement restrictions was effective in controlling the epidemic, 112 herd outbreaks occurred up to 6 months after the end of the mass-vaccination campaign. Mass-vaccination and movement restrictions might be an effective strategy to control FMD; however, the time taken to end large, national epidemics might be >1 year.     

Differences among restriction endonuclease DNA fingerprints of Pennsylvania field isolates, vaccine strains, and challenge strains of infectious laryngotracheitis virus.

Restriction endonuclease fingerprints of infectious laryngotracheitis virus (ILTV) DNA from 13 Pennsylvania field isolates, embryo-propagated and tissue-culture-propagated vaccine strains, and three reference strains were compared. These comparisons were made to evaluate the possible contribution of mutation of ILTV vaccine strains to recent outbreaks of infectious laryngotracheitis (ILT) in Pennsylvania. Six different restriction enzymes were used to generate the fingerprints. Differences in DNA banding patterns were revealed between the currently used ILTV vaccine strains and six of the 13 field isolates. Even greater DNA banding pattern differences were found between the older ILTV reference strains and the vaccine strains. The ILTV DNA fingerprints generated in the present study suggest that at least five different strains of ILTV have contributed to the outbreaks of ILT that have occurred since 1987 in Pennsylvania.     

The use of pulsed-field gel electrophoresis to investigate the epidemiology of Mycoplasma bovis in French calf feedlots

Mycoplasma bovis is a major cause of respiratory outbreaks in cattle feedlots. In this study pulsed-field gel electrophoresis (PFGE) was used to trace field strains and provide information on M. bovis patterns of spread in calf feedlots. The suitability of KpnI, MluI and SmaI restriction enzymes was assessed on different sets of strains. The discriminative power of the first two enzymes was first assessed using 28 epidemiologically unrelated strains; stability was 100% on multiple isolates from in vivo experimental infection. Thirty-nine field isolates from six feedlots were then evaluated. In contrast to the unique fingerprints displayed by the unrelated strains, the isolates from the feedlots showed identical patterns at the time of the outbreak of respiratory disease and 4 weeks later. The PFGE typing results suggest that M. bovis strains follow a clonal epidemic spread pattern at the herd level and that the same strain persists in calves of the herd after the clinical signs have disappeared.     

Haemophilus somnus Infections I. A Ten Year (1969-1978) Retrospective Study of Losses in Cattle Herds in Western Canada

A total of 838 outbreaks of fatal Haemophilus somnus infections in herds of cattle were diagnosed at provincial veterinary laboratories in Manitoba, Saskatchewan, Alberta and British Columbia during the period 1969-1978. The index cases from these outbreaks included 759 cases of thromboembolic meningoencephalitis, 78 cases of fibrinous pneumonia with pleuritis and one case of H. somnus abortion. The epizootics were subdivided on the basis of province, class and age of cattle and seasonal occurrence. Most outbreaks occurred in a feedlot-type of operation, approximately four weeks after arrival of the cattle. There was often a history of respiratory disease prior to an outbreak and in some cases thromboembolic meningoencephalitis had occurred in the herd the preceding year. The average morbidity-mortality ratio was 2.7/1. The average economic loss per herd was $3 190 based on an average of 15 sick animals and five deaths per affected herd.     

Influenza in swine in Belgium (1969–1986) Epizootiologic aspects

From 1984 until 1986, influenza isolates were obtained from 59 outbreaks of respiratory tract disease in Belgium. In 21 of the outbreaks, H₃N₂-influenza virus isolates, related to the human A/Port Chalmers/1/73 strain were obtained. All other isolates were H₁N₁-influenza virus strains. The prevalence of variants of the human H₃N₂-influenza virus in the Belgium swine population was determined by examining sow sera which had been collected between 1969 and 1984. The results of this serological study showed that, although a Port Chalmers-like strain was associated with outbreaks of respiratory tract disease in swine only since 1984, such strain was already present in the swine population in 1974, when a low percentage of sow sera (7%) reacted with A/Port Chalmers/1/73. Between 1975 and 1984, antibody against this strain were present in 28–61% of the sera. Furthermore, 3–6% of the sera collected between 1971 and 1980 reacted with the A/Hong Kong/1/68 strain. There were no indications that more recent human H₃N₂-strains (A/Texas/1/77, A/Bangkok/1/79 and A/Belgium/2/81) circulated in the Belgian swine population.     

Spatial clustering of swine influenza in Ontario on the basis of herd-level disease status with different misclassification errors

This approach maximizes sensitivity of serology-based monitoring systems by considering spatial clustering of herds classified as false positive by herd testing, allowing outbreaks to be detected in an early phase. The primary objective of this study was to determine whether swine herds infected with influenza viruses cluster in space, and if so, where they cluster. The secondary objective was to investigate the combining of a multivariate spatial scan statistic with herd test results to maximize the sensitivity of the surveillance system for swine influenza. We tested for spatial clustering of swine influenza using the Cuzick–Edwards test as a global test. The location of the most likely spatial clusters of cases for each subtype and strain in a sample of 65 sow and 72 finisher herds in 2001 (Ontario, Canada), and 76 sow herds in 2003 (Ontario, Canada) was determined by a spatial scan statistic in a purely spatial Bernoulli model based on single and multiple datasets.

A case herd was defined by true herd-disease status for sow or finisher herds tested for H1N1, and by apparent herd-disease status for sow herds tested for two H3N2 strains (A/Swine/Colorado/1/77 (Sw/Col/77) and A/Swine/Texas/4199-2/98 (Sw/Tex/98)). In sow herds, there was no statistically significant clustering of H1N1 influenza after adjustment for pig-farm density. Similarly, spatial clustering was not found in finisher herds. In contrast, clustering of H3N2 Sw/Col/77 (prevalence ratio = 12.5) and H3N2 Sw/Tex/98 (prevalence ratio = 15) was identified in an area close to a region with documented isolation of avian influenza isolates from pigs.

For the H1N1 subtype tested by ELISA, we used an approach that minimized overall misclassification at the herd level. This could be more applicable for detecting clusters of positive farms when herd prevalence is moderate to high than when herd prevalence is low. For the H3N2 strains we used an approach that maximized herd-level sensitivity by minimizing the herd cut-off. This is useful in situations where prevalence of the pathogen is low. The results of applying a multivariate spatial scan statistic approach, led us to generate the hypothesis that an unknown variant of influenza of avian origin was circulating in swine herds close to an area where avian strains had previously been isolated from swine. Maximizing herd sensitivity and linking it with the spatial information can be of use for monitoring of pathogens that exhibit the potential for rapid antigenic change, which, consequently, might then lead to diminished cross-reactivity of routinely used assays and lower test sensitivity for the newly emerged variants. Veterinary authorities might incorporate this approach into animal disease surveillance programs that either substantiate freedom from disease, or are aimed at detecting early incursion of a pathogen, such as influenza virus, or both.     

Actinobacillus suis septicemia in mature swine: two outbreaks resembling erysipelas

In the winter of 1987/88 a previously unrecognized septicemic disease syndrome — actinobacillosis in mature sows and gilts — was diagnosed in two minimal-disease swine herds in southwestern Ontario. In herd 1, 34 sows, 2 boars, 13 feeder pigs, and 30 suckling pigs were affected; 11 sows, 2 feeders, and 18 suckling pigs died. In herd 2, 13 sows and 1 feeder pig were affected; 1 sow and 1 feeder pig died. The disease was manifested by moderate fever (39-40.5°C), round or rhomboid erythematous skin lesions, and inappetence. Sudden deaths without previous clinical signs were frequent. Histologically, coccobacillary thromboemboli in superficial and deep dermal vessels were associated with infarcted dermal and epidermal tissues. The causative organism, Actinobacillus suis, was isolated from the affected pigs. Treatment with commonly used antibacterial drugs was effective.

In many respects, the disease resembled acute swine erysipelas and presented diagnostic problems for this reason.

     

Antigenic characterization of IBDV field isolates by their reactivity with a panel of monoclonal antibodies

Recently Infectious Bursal Disease Virus isolates have been described in USA displaying an antigenic drift. Many of the new isolates were very virulent for chickens. In several European countries severe outbreaks of Gumboro disease have also been reported from vaccinated and non-vaccinated flocks. Since vaccinated SPF birds were shown to be protected against challenge infection with the new isolates under laboratory conditions, a more detailed investigation of the European isolates is wanted. The similarity between the European and US field situation got us to use a panel of monoclonal antibodies (MCAs) previously applied to characterize US strains for testing European isolates. An antigen capture ELISA has been carried out directly on bursa homogenates of chickens form the field. One European (F52/70) and two US (Var. E and GLS-5) strains have been included as reference viruses. From the results presented here it can be concluded that the European isolates (Netherlands, France, UK, Germany, Jugoslavia and Spain) did not undergo the same antigenic drift as the US strains. A more extensive analysis of the isolates will be done to elucidate their role for disease outbreaks.     

The Characterization of Infectious Bursal Disease Virus Strains/Isolates from Field Outbreaks in India

Pahar, B. and Rai, A., 1997. The characterization of infectious bursal disease virus strains/isolates from field outbreaks in India. Veterinary Research Communications, 21 (4), 289-301Three infectious bursal disease virus (IBDV) isolates were adapted to culture in chick embryo fibroblast cells in which they produced a cytopathic effect. The isolates were identified as IBDV by virus neutralization tests using a standard hyperimmune serum against infectious bursal disease, physicochemical properties and their pathogenicity in chick embryos and chicks. The IBDV S394 strain was antigenically different from IBDV S194/IBDV S494 as well as from the IBDV Intermediate Georgia strain, one of the vaccine strains in use in India.     

Use of an inhibitor typing scheme to study the epidemiology of Streptococcus uberis mastitis

An inhibitor typing scheme, based on the production of and sensitivity to bacteriocin-like inhibitor substances was used to identify strains of Streptococcus uberis obtained from skin swabs and milk samples of dairy cows. Thirty-nine isolates from one herd were compared, with one isolate examined per site for any sampling day. Eighteen different inhibitor profiles were observed from these isolates. When several isolates were obtained from various skin sites on a cow on the same day, the inhibitor profiles were all different. In three cases, Str. uberis was simultaneously isolated from milk sample and teat surface of the same quarter, but similar inhibitor profiles were only observed for one pair of isolates. Furthermore, when several isolates were obtained by repeated swabbing of a single skin site on a cow on the same day, differences in the inhibitor profiles were again seen. It is likely that numerous strains of Str. uberis are capable of producing clinical mastitis since a comparison of ten isolates obtained from cases of clinical mastitis revealed eight different inhibitor profiles. Monthly sampling (April-November) of eleven cows revealed that Str. uberis could be isolated from the skin of the abdominal wall, medial thigh, udder and teats, but was not isolated from the rectum of any of the cows. Str. uberis was more frequently isolated from the skin and milk samples during the winter when the cows had been dried off, than during the spring and autumn.     

Occurrence and characteristics of CS31A antigen-producing Escherichia coli in calves with diarrhoea and septicaemia in Argentina

CS31A is a K88-related non-fimbrial adhesin first described on Escherichia coli strains isolated from diarrhoeic and septicaemic calves. In this report, CS31A antigen was screened by immunological methods and confirmed by PCR among bovine E. coli isolates. In addition, CS31A-producing strains were characterized with respect to different fimbrial antigens, O-serogroup and other properties related to virulence. Faecal or tissue specimens of 100 diarrhoeic or septicaemic calves and 27 older cattle with different pathologies from 71 outbreaks or individual cases that occurred in Buenos Aires province, Argentina, were examined. CS31A + E. coli strains were isolated from 21 (21.0%) calves from 16 outbreaks or individual cases. No CS31A + E. coli was detected in samples from cattle more than 1 year old. Fimbriae F5, F41, F17a and F17b were not detected among the CS31A-producing strains. Three (14.3%) of the CS31A+ E. coli strains expressed the F17c fimbria. All of the 21 isolates exhibited at least one property of septicaemic strains (resistance to serum, production of aerobactin or colicins) but none of them demonstrated heat-stable enterotoxigenic activity. CS31A + E. coli isolates belonged to 10 serogroups, more commonly O8, O7, O17 and O21. The results obtained here confirm the worldwide distribution of CS31A antigen in bovine E. coli strains. However, CS31A + or CS31A + /F17c + E. coli were less frequently isolated than they were in North hemisphere countries.     

A serological and biochemical study of new field isolates of foot-and-mouth disease virus type A in Peru, 1975 to 1981

Three foot-and-mouth disease virus type A isolates recovered from field outbreaks in the Department of San Martin, Peru, during the period 1975 to 1981 were compared with each other, and the South American vaccine strains A24 and A27, by complement fixation (CF), virus neutralization (VN) and polyacrylamide gel electrophoresis (PAGE). Complement fixation and VN tests gave comparable results distinguishing the field isolates from each other and from the vaccine strains. Analysis of the structural polypeptides by PAGE also showed clear differences between all the viruses examined. Samples from tissue culture passaged and mouse adapted strains of one of the field isolates gave identical patterns in PAGE, but differences were observed in the polypeptide pattern of the A24/BRA/55 strain and the Peru vaccine strain, which were serologically indistinguishable. Results illustrate a continued antigenic variation in an endemic area where vaccination has been used; however, asymmetric serological reactions between the A24 vaccine strain and the most recent field isolate indicated that a vaccine incorporating A24 should still give adequate protection.     

Bovine virus diarrhea--clinical syndromes in dairy herds

Bovine Virus Diarrhea (BVDV) was diagnosed as the major etiological agent in 10 dairy herd disease outbreaks. The outbreaks varied between herds in time of onset in individual cattle, signs, morbidity, and clinical course. A definitive diagnosis was obtained by viral isolation from whole blood samples in each herd. Each herd problem and its clinical course was described in detail. A discussion of current knowledge pertaining to BVD--the disease and the virus--follows. The importance of strain variation relative to disease production and prophylaxis was highlighted.     

Typing by Polymerase Chain Reaction of Buffalo Rotaviruses Isolated in Italy

Six group A rotaviruses were isolated in Italy from buffaloes during different outbreaks of calf diarrhoea occurring in the same dairy herd over a 5-year period of observation. The isolates were characterized by polymerase chain reaction assay for G- and P-type antigens. G8 and P1 were the types most frequently isolated.