Other bacterial diseases
A new, previously unrecognized Mycoplasma species from farmed crocodiles; Mycoplasma crocodyli was first reported in Zimbabwe. The new Mycoplasma species causes polyarthritis and pneumonia in crocodiles. Tetracycline treatment of the cases by injection and in the feed proved to be effective in ameliorating clinical signs but does not prevent relapses. The use of an autogenous vaccine produced from M. crocodyli proved more effective in alleviating the disease manifestations than antibiotic therapy. In addition to the usual organs infected, Mycoplasma ovipneumoniae (MO) reported in communal flocks of goats infected the thymus, which has not been previously reported with any Mycoplasma spp. The goats did not produce detectable serum antibodies to M. ovipneumoniae and were not reactive to MO antigen in a tuberculin-type hypersensitivity test; indicating the possibility of an immunotolerance state responsible for failure to develop clinical pneumonia.
Pasteurellosis research revealed the Pasteurella spp (P. multocida, P. haemolytica, P. canis, P. gallinarum, P. stomatitis&P. dagmatis) with P. multocida (75%) and P. haemolytica (18%) being the dominant species. Serotyping studies demonstrated presence of three capsular serogroups [A (59%), B (5%) & D (14%)] with serogroup A being widely distributed among various animal hosts and the most prevalent serotype while serogroups E & F are absent. The research also highlights the first isolation of Communicable Diseases Centre (CDC) group EF-4 from dogs. A wide variety of disease conditions in different hosts due to Pasteurella spp have been recorded. Hosts included all domestic animals (cats, cattle, chickens, dogs, goats, horses, pigs, rabbits & sheep) in Zimbabwe, and also some wild animals (crocodiles).
Research on actinobacillosis enabled detailed descriptions of Zimbabwean Actinobacillus spp strains that includes; A. lignieresii, A. equuli, A. suis, Taxon 9 (causing ‘sleepy foal’ disease) and Taxon 11. The studies resulted in the first time isolation of A. lignieresii from a post-operative wound in a cat and from an ostrich.
A total of 29 scientific articles related to viral diseases have been published to date. The research has focused on the following viral diseases: rabies in dogs, humans and wildlife; feline leukemia in domestic cats; distemper in dogs; Newcastle disease (NCD) in ostriches (Struthio camelus); bovine virus diarrhoea – mucosal complex in cattle; beak and feather disease in Lillian’s Lovebirds (Agapornis lillianae); contagious ecthyma in goats; infectious pustular vulvo-vaginitis (IPV) in cattle; bovine viral leucosis; porcine rotavirus infection in pigs; bovine ephemeral fever and canine parvovirus infection. Rabies publications accounted for approximately 38% (11/29) of the articles.Only two viral zoonotic diseases, contagious ecthyma and rabies have been researched on by the Faculty. The research focused on several aspects such as epidemiology, prevalence, clinical features, diagnosis, control and prevention. Highlights of some of the research findings are outlined below.
Psittacine beak and feather disease a well-known viral disease (caused by a Circovirus) not previously diagnosed in Zimbabwe was shown to occur in the country resulting in 100% mortality and about 91% morbidity in lovebirds. Further investigations showed that the disease mostly affected two species of lovebirds; Agapornis nigrigensis and A. lillianae and had a different clinical course than that reported elsewhere. Based on a different disease course and viral ultrastructural differences, it was concluded that the disease could be due to a different virus or that there are different strains of the virus in the country.
Dogs were shown to be themajor important vector of rabies in the country (over 90% of human cases are due to dog bites); withmost dog and human rabies cases being recorded in communal areas. Animal-to-human transmission is highest during the dry months of July to November. A significant inverse relationship was shown between vaccination coverage and number of dog rabies cases; indicating that dog rabies control is a more cost-effective measure for preventing human rabies. Jackals are the second major maintenance hosts and both species; Canis adustus (side-striped jackals) and C. mesomelas(black-backed jackals) are able to maintain rabies epidemics independently of other species. Control studies showed thata baiting system of sponge baits containing a placebo liquid, rhodamine B as a biomarker and a pungent attractant was efficient in delivering oral vaccine to dog populations. For jackals, a bait vaccine (SAG-2) was found sufficient to immunize wild jackal populations when given orally using chicken head baits.
With regard to other viral diseases; the studies showed high prevalence ofcanine distemper virus (CDV))and canine parvovirus (CPV) in dogs, bovine-virus diarrhoea-virus (BVDV) and bovine ephemeral fever (BEF) in cattle, porcine rotavirus in pigletsand feline leukemia virus (FeLV)in cats. CDV infection is likely to play an important role in the high morbidity and mortality seen in young communal dogs. CPV was found to be the most frequently encountered viral infection of urban dogs with in excess of 2500 cases per annum. The enzyme-linked immunosorbent assay (ELISA) is reported to be more suitable for the routine diagnosis of BVDV whilst haematological and biochemical changes in a single blood sample do not provide a reliable diagnostic aid for BEF. Selenium deficiency was associated with respiratory distress and subcutaneous emphysema in cattle with BEF while rotavirus infection in piglets was significantly associated with diarrhoea. Intact cats raised in multicat housing systems that have access to outdoor life are at a higher risk of being FeLV positive and the disease is associated with autoimmune haemolytic anaemia. The studies also serologically demonstrated the presence of antibodies against NCD virus in naturally exposed ostriches and the first confirmed isolation of the IPV virus in cattle in the country. Arboviruses’ vector studies showed that Culicoides imicola is the abundant species followed by C. zuluensisand C. bolitinos.Culicoides imicola is a known vector for blue tongue and African horse sickness viruses.
Tumours and other pathological conditions
Currently this category has a total of 72 articles published. However, a total of 32 scientific papers related to tumours in dogs, cattle and horses have so far been published. Of the 32 articles published, most (56.3%, 18/32) were on dog tumours and 40.6% (13/32) were on cattle tumours. Only one article was published on tumours (adenocarcinoma) in horses. Studied tumours in dogs included astrocytoma, carotid and aortic body tumours, cutaneous neoplasms, epitheliomata, haemangiosarcoma, leiomyosarcoma, melanomas, meningioma, mesothelioma, osteosarcoma and canine transmissible venereal tumours (CTVT) whilst in cattle it was ocular squamous cell carcinoma (OSCC), vulval carcinomas and vulval papillomas. Approximately 41% (13/32) of the articles focused on treatment of tumours, mostly on therapy of OSCC in cattle using interleukin 2 (IL2). Highlights of some of the research findings are outlined below.
Mast cell tumours, squamous cell carcinomas, perianal gland adenomas, lymphomas, benign melanomas, haemangiosarcomas, sebaceous gland adenomas, fibrosarcomas, lipomas and malignant melanomas were reported to be the most common cutaneous tumours in dogs. It has been found that in Zimbabwe there is a greater prevalence of lymphomas and of tumours associated with increased exposure to ultraviolet light (squamous cell carcinomas, haemangiosarcomas and melanomas) in dogs. The prevalence of prostatic neoplasia was found to be low in dogs. Although digital rectal examination (DRE) appeared to be a good test to screen subclinical prostatic disease, it was found to have a low sensitivity and needs to be combined with other more sensitive techniques.Studies on CTVT suggests that mast cells play a role in CTVT progression that mast cell count (MCC) could be used as one of the histological factors to indicate growth stage of CTVT. Similarly, MCC and micro-vessel density (MVD) were demonstrated to have a prognostic significance in canine melanocytic tumours. However, clinicopathological factors and histopathological grading remain the most practical parameters in cancer decision-making and management. Combined bacillus Calmette-Guerin (BCG) and vincristine therapy was found to be more effective than vincristine in treating CTVT, suggesting that the clinical course of this disease may be altered by immunochemotherapy.
OSCC was detected more in Simmental cattle with periorbital white skin.Therapy studies have shown that local IL- 2 therapy can be successfully used to treat OSCC with over 60% complete regressions. In addition, IL-2 can be used in combination with IL-12 for the treatment of OSCC but however, combination therapy does not improve the outcome in comparison to IL-2 as a single therapy. Local IL-2 treatment of bovine vulval papilloma carcinoma complex (BVPCC)was also shown to be feasible and effective under field conditions in Zimbabwe. This is of considerable economic importance, particularly for dairy farmers, as cows in Zimbabwe remain productive for a prolonged period. However, whereas a complete regression is obtained in OSCC mainly stable disease is attained in BVPCC. BCGtreatment also induced total regression of vulval carcinomas, limited regression in advanced papillomas, but had little or no effect on the early stages of papillomas in cattle.