Equine viral encephalomyelitis in Canada: a review of known and potential causes

Rabies, equine herpesvirus type I, and eastern and western encephalomyelitis viruses, known causes of equine neurological disease, are reviewed with emphasis on epidemiology, pathogenesis, clinical signs, and diagnosis.

Several arboviruses known to be active in Canada and capable of producing neurological disease in humans (Powassan, St. Louis encephalitis, snowshoe hare, and Jamestown Canyon viruses) are discussed as potential causes of encephalomyelitis in horses.

     

Rabies in Canada - history, epidemiology and control

Rabies first became evident in Canada during the late 18th and early 19th centuries. However, only a few sporadic outbreaks, mainly in domestic animals, were noted before 1945.

Rabies in foxes spread into the Canadian provinces from the Arctic regions during the late 1940s. The disease gradually died out in most areas except Ontario. A second major outbreak, involving skunks, progressed from North Dakota into the Prairie provinces during the late 1950s and 1960s. Today, the major problem areas in Canada with respect to rabies are southern Ontario, which accounts for 85% of the Canadian diagnoses, and the Prairie provinces where rabies is enzootic in skunks.

Rabies is rare in humans in Canada; however more than 40,000 cases have been reported in wild and domestic animals since 1958. Control of rabies is currently being undertaken through vaccination of domestic animals and wildlife, population reduction of wildlife vectors, and human preexposure rabies vaccination.

     

Heartworm in dogs in Canada in 1983

In late December 1983, 2 800 veterinarians across Canada were sent a questionnaire in order to assess the status of heartworm disease in Canada in 1983 and 26% of them responded. Veterinarians reported that 59 504 dogs were blood-tested to check for microfilariae and 771 dogs (1.30% of those tested) were found with Dirofilaria immitis. Heartworm disease was diagnosed in all provinces except New Brunswick and Newfoundland but most (733) of the cases were in Ontario.

Heartworm disease was found most frequently in companion dogs over three years of age maintained mainly outdoors in rural areas. About 31% of the cases were observed with clinical signs of heartworm disease and 64% had a history of not having left Canada. Southwestern Ontario continues to be the focus of the infection and most of the dogs there had not left the province previously.

     

Pulmonary adenomatosis (jaagsiekte) of sheep in Canada

Sheep pulmonary adenomatosis has recently been reported in Canada. The literature is briefly reviewed and an account of the present status of the disease in Canada is described.

Sheep pulmonary adenomatosis was first diagnosed in Canada in December 1979 in a first generation descendent of sheep imported from Great Britain. In March 1980 two further cases of sheep pulmonary adenomatosis were diagnosed in a second flock. A total of 43 sheep involving eight flocks from five provinces have been observed from December, 1979 to May, 1981. The clinical signs and laboratory findings were similar to those described in sheep from other countries. It is estimated that 30% of Canadian flocks may contain sheep imported from Great Britain during the 1970's.

     

"Benchmark" - a large observational study of Ontario beef breeding herds: Study design and collection of data

The methods used in a large field study which investigated the health and productivity of Ontario beef breeding herds are described. Beginning in the calving season of 1986, 180 breeding herds on 170 randomly sampled farms were followed for a two year period, using producer records and annual farm visits.

The response (cooperation) rate among the eligible producers initially contacted was 70%. Approximately two-thirds of producers maintained individual animal records, primarily calving season records. Approximately 40% recorded disease occurrences.

The advantages, disadvantages, and interpretation of “on-farm” observational studies are discussed.

     

Growth of Foot-and-Mouth Disease Virus in Dispersed Tissue Cells: I. Methods of Production

Methods are described for rapid and economical production of large quantities of foot-and-mouth disease virus in stationary cultures of trypsin-dispersed bovine kidney cells in a simple medium. Yields of between 10⁷ and 10⁸ plaque-forming units per milliliter were obtained from serum-free cultures containing approximately a million and a half viable trypsin-dispersed cells per milliliter.

Some of the advantages and disadvantages of these methods of virus production are discussed.

     

Heartworm in dogs in Canada in 1985

In late December 1985, 1485 institutional veterinarians and small and mixed animal clinics across Canada were sent a questionnaire in order to assess the status of Dirofilaria immitis in Canada in 1985 and 44% of them responded. Veterinarians reported that 137,300 dogs were blood-tested to check for microfilariae and 1210 dogs were found with heartworm. Another 36 dogs were amicrofilaremic but diagnosed with heartworm disease to give the total number diagnosed in 1985 as 1247 (0.91%).

Heartworm was reported from all provinces except Prince Edward Island, Newfoundland and Saskatchewan but most (1126) of the cases were in Ontario. Southwestern Ontario continued to be the primary focus of the infection in Canada. From Quebec, 91 cases were reported mostly from and around Montreal. From Manitoba, 19 cases were reported from Winnipeg and surrounding areas. Heartworm was found most frequently in companion dogs over three years of age maintained mainly outdoors in rural areas. About 28% of the cases were observed with clinical signs of heartworm disease and 78% had a history of not having left Canada.

     

Heartworm in dogs in Canada in 1986

In late December 1986, 1224 institutional veterinarians and small and mixed animal clinics across Canada were sent a questionnaire in order to assess the status of Dirofilaria immitis in Canada in 1986; 46% of them responded. Veterinarians reported that 150,989 dogs were blood-tested for microfilariae and 869 dogs were found with heartworm. Another 65 dogs were amicrofilaremic but diagnosed with heartworm disease and one was found with heartworm at necropsy to give the total number diagnosed in 1986 as 935 (0.62%).

Heartworm was reported from Manitoba, New Brunswick, Ontario and Quebec, but most (810) of the cases were from Ontario. South-western Ontario continued to be the primary focus of the infection in Canada. There were 103 cases reported from Quebec, mostly from and around Montreal, and 21 cases from Manitoba, from Winnipeg and surrounding areas. Heartworm was found most frequently in companion dogs over three years of age maintained mainly outdoors in rural areas. About 33% of the cases were observed with clinical signs of heartworm disease and 81% had a history of not having left Canada.

     

Heartworm in dogs in Canada in 1984

In late December 1984, 1853 institutional veterinarians and small and mixed animal clinics across Canada were sent a questionnaire in order to assess the status of Dirofilaria immitis in Canada in 1984 and 35% of them responded. Veterinarians reported that 97,794 dogs were blood-tested to check for microfilariae and 1417 dogs (1.45% of those tested) were found with heartworm. Another 34 dogs were amicrofilaremic, but were diagnosed as having heartworm disease, to give the total number diagnosed in 1984 as 1451 (1.48%). Heartworm was reported from all provinces except Prince Edward Island and Newfoundland but most (1310) of the cases were in Ontario. In Quebec, 126 cases were reported mostly from west of Montreal.

Heartworm was found most frequently in companion dogs over three years of age maintained mainly outdoors in rural areas. About 27% of the cases were observed with clinical signs of heartworm disease and 72% had a history of not having left Canada. Southwestern Ontario continued to be the primary focus of the infection.

     

Case Report: Outbreak of Bumper Car Disease Caused by Anophryoides haemophila in a Lobster Holding Facility in Nova Scotia,Canada

Abstract

This case report provides pathologic and confirmatory molecular characterization of an outbreak of bumper car disease caused by the scuticociliate Anophryoides haemophila in American lobster Homarus americanus, from a commercial holding facility in Nova Scotia, Canada. Although sporadically and anecdotally reported to be present in Atlantic Canada, this is the first report detailing observations from a natural outbreak of bumper car disease by gross and microscopic pathology and its positive identification by small subunit rRNA gene sequencing. Randomly amplified polymorphic DNA analysis confirmed that the genotype of the present outbreak isolate is identical to the original isolate of A. haemophila reported from Maine lobsters in 1993.     

The Canadian Beef Industry

The cattle industry in Canada has changed greatly over the past several decades. Size of the national dairy herd has reduced steadily but this reduction has been more than offset by an increase in the beef herd.

As the dairy herd has decreased, the role of the Holstein has increased. The genetic improvement of the Canadian Holstein, based on selection procedures emphasizing progeny performance and mediated through increasing use of artificial insemination, has earned the breed a strong international reputation. This is reflected by the increasing international demand for semen.

The strongest growth of the national beef herd occurred during a period of brisk import activity. Several of the new nonBritish breeds are now well established. Their advent on the Canadian scene rekindled interest in crossbreeding and systematic crossbreeding programs designed to make controlled use of heterozygosity are in the process of development. The new breeds of major importance at this time combine rapid growth rate with desirable carcass characteristics, specifically lean content. This, coupled with the carcass grade standards inaugurated in 1972, has resulted in improved efficiency of lean meat production.

Importation activity has waned and a review of the production credentials of breeds not yet in Canada suggests little likelihood that they will contribute meaningfully to Canadian production. The numerous beef breeds now in Canada are presently undergoing a process of applied evaluation and relatively few of them seem destined to make a lasting contribution.

The future of the cattle industry will be determined largely by economic developments. However, the ability of the ruminant to utilize food materials that do not compete directly with human demands should ensure an enduring future.

     

Strains of Rabies Virus Available for Preparation of Sylvatic Rabies Vaccines with Special Reference to Vaccines Prepared in Cell Culture

Rabies vaccines for use as a preventive in wildlife have not yet been licensed.

There are several vaccines which, based on tests in dogs, merit trial especially in foxes and skunks and these are summarized in a table.

Trials are being conducted in Canada on the effectiveness of several of these vaccines in foxes and skunks.

     

A Brief Review of Bovine Coccidiosis in Western Canada

Coccidiosis of beef cattle, in both its enteric and nervous forms, seen in feedlots in Western Canada is discussed. Cases of coccidiosis accompanied by nervous signs, occasionally up to 30% of those affected enterically, are most common during the coldest winter months. The pathogenesis of the nervous form of the disease is unknown. Clinical management of disease outbreaks using various chemotherapeutics is described. The importance of using anticoccidial drugs before the onset of clinical signs in cattle in contact with sick animals is discussed.     

Fish Disease and Biosecurity: Attitudes,Beliefs, and Perceptions of Managers and Owners of Commercial Finfish Recirculating Facilities in the United States and Canada

Abstract

In recirculation finfish facilities in the United States and Canada, biosecurity utilization is neither consistent nor uniform. Seeking reasons for this situation, we examined the beliefs, perceptions, and attitudes of managers and owners of such facilities about fish disease and biosecurity utilization. A questionnaire was mailed in the fall of 2001 to the managers and owners of 152 finfish-rearing recirculation facilities in the United States and Canada to gather information on their attitudes, beliefs, and perceptions regarding fish disease and biosecurity. The response rate to the survey was 86%. This paper reports on a subset of the overall responses, the responses of managers and owners who identified their facility as a business operation. Although respondents had a positive attitude towards biosecurity utilization, they had different beliefs about which disease types were of greatest concern for their farm. Respondents also had differing perceptions on the risk of disease transmission associated with different activities on their farms. In addition, respondents had various beliefs about the practicality and effectiveness of different biosecurity measures and why the practice of biosecurity was important to their farms. This study gives quantitative evidence that different fish farmers perceive disease and the practice of biosecurity differently. This study indicates that recognition of the human dimensions element is an important first step in the creation of biosecurity policies, strategies, and procedures that will be readily accepted and implemented and consistently applied by fish farmers on their farms. The findings challenge the heretofore traditionally accepted belief that poor biosecurity practice on a farm is primarily related to lack of knowledge about biosecurity.     

Evolving perceptions of bluetongue: A challenge for government and industry

From the first discovery of bluetongue virus activity in Canada in the Okanagan Valley of British Columbia in 1976 to the present, more than 175,000 sera from cattle in Canada have been tested for the presence of bluetongue antibody during the course of disease investigations and during regional or national surveys. Serological reactors have been detected only in cattle resident in the Okanagan Valley or in those originating in the United States.

Despite the regional nature of the distribution of antibody to bluetongue, international trade sanctions were applied on a nationwide basis. The strategy of the federal government for limiting the international, as well as the domestic, impact of bluetongue has evolved over the past 15 years as the epizootiology of bluetongue has become better understood. This new information is also ameliorating somewhat international attitudes toward nations which experience infections.

     

Bovine Genital Mycoplasmosis

Infection, lesions and clinical significance of Acheloplasmas, Mycoplasma bovis and Mycoplasma bovigenitalium in genital disease of cattle are described. A more detailed account is given of ureaplasma infections. Acute and chronic forms of granular vulvitis in both field and experimental disease are described as well as the role of the organism in abortion.

Recovery rates of ureaplasma and mycoplasma from semen and preputial washings in bulls are outlined and their significance in disease is discussed. There are problems in differentiating pathogenic from nonpathogenic isolates. Methods are being developed to treat semen for these organisms.

This paper provides a concise summary of clinical and microbiological aspects of bovine genital mycoplasmosis.

     

Reproductive Problems in the Management of Dairy Cattle

The author outlines the significance of herd health programs and the manner in which they are explained, and developed with clients.

Reproductive problems account for a major part of the herd health program, but also included are nutrition, preventive vaccination programs, calf management, mastitis surveillance, feet and leg problems, worming, dehorning, castration, record keeping and identification.

The differential diagnoses of reproductive problems are discussed in detail and specific treatments are outlined. The prognosis of various conditions in relationship to treatment is emphasized.

     

Somatic cell counts in bovine milk

Factors which influence somatic cell counts in bovine milk are reviewed and guidelines for their interpretation are presented. It is suggested that the thresholds of 300 000 and 250 000 cells/mL be used to identify infected quarters and cows respectively. However, it is stressed that somatic cell counts are general indicators of udder health which are subject to the influence of many factors. Therefore the evaluation of several successive counts is preferable to the interpretation of an individual count.

Relationships between somatic cell counts and both milk production and milk composition are discussed. Subclinical mastitis reduces milk quality and decreases yield although the relationship between production loss and somatic cell count requires clarification. Finally the availability of somatic cell counting programs in Canada is presented.

     

Isolation of Mycoplasma mycoides subspecies mycoides from Polyarthritis and Mastitis of Goats in Canada

The clinical signs, pathomorphological changes, and microbiological findings in Canadian goats infected with Mycoplasma mycoides subspecies mycoides are discussed. The disease affected mainly young goats and was characterized by septicemia and polyarthritis. Mastitis followed by septicemia was seen in two mature goats. The diagnosis was made by culture and identification of the mycoplasma. Infected goats without clinical signs were identified by cultural and serological (complement fixation) techniques. Healthy carriers are presumably able to transmit the infection and may have brought the disease to Canada.