Oral vaccination of brushtail possums with BCG: Investigation into factors that may influence vaccine efficacy and determination of duration of protection

AIMS: To determine factors that may influence the efficacy of an oral pelleted vaccine containing Mycobacterium bovis bacille Calmette-Guérin (BCG) to induce protection of brushtail possums against tuberculosis. To determine the duration of protective immunity following oral administration of BCG.

METHODS: In Study 1, a group of possums (n=7) was immunised by feeding 10 pellets containing dead Pasteur BCG, followed 15 weeks later with a single pellet of live Pasteur BCG. At that time, four other groups of possums (n=7 per group) were given a single pellet of live Pasteur BCG orally, a single pellet of live Danish BCG orally, 10 pellets of live Pasteur BCG orally, or a subcutaneous injection of live Pasteur BCG. For the oral pelleted vaccines, BCG was formulated into a lipid matrix, and each pellet contained approximately 10⁷ colony forming units (cfu) of BCG, while the vaccine injected subcutaneously contained 10⁶ cfu of BCG. A sixth, non-vaccinated, group (n=7) served as a control. All possums were challenged by the aerosol route with a low dose of virulent M. bovis 7 weeks after vaccination, and killed 7–8 weeks after challenge. Protection against challenge with M. bovis was assessed from pathological and bacteriological findings.

In Study 2, lipid-formulated live Danish BCG was administered orally to three groups of possums (10–11 per group), and these possums were challenged with virulent M. bovis 8, 29 or 54 weeks later. The possums were killed 7 weeks after challenge, to assess protection in comparison to a non-vaccinated group.

RESULTS: The results from Study 1 showed that vaccine efficacy was not adversely affected by feeding dead BCG prior to live BCG. Feeding 10 vaccine pellets induced a level of protection similar to feeding a single pellet. Protection was similar when feeding possums a single pellet containing the Pasteur or Danish strains of BCG. All vaccinated groups had significantly reduced pathological changes or bacterial counts when compared to the non-vaccinated group. In Study 2, oral administration of Danish BCG induced protection against challenge with M. bovis, which persisted for at least 54 weeks after vaccination. Some protection was observed in possums challenged 54 weeks after vaccination, but this protection was significantly less than that observed in groups vaccinated 29 or 8 weeks prior to challenge. There was a strong relationship between the proportion of animals producing positive lymphocyte proliferation responses to M. bovis antigens and protection against challenge with M. bovis.

CONCLUSIONS: Factors considered potentially capable of interfering with vaccination, including feeding dead BCG to possums prior to feeding live BCG, feeding multiple doses of BCG at one time, and changing strains of BCG, were shown not to interfere with the acquisition of protective immune responses in possums. Protection against tuberculosis was undiminished up to 29 weeks after vaccination with BCG administered orally. It is concluded that vaccination of possums by feeding pellets containing BCG is a robust and efficient approach to enhance the resistance of these animals to tuberculosis.     

The case of the missing marmots: Are metapopulation dynamics or range-wide declines responsible?

In the mid-1990s, anecdotal reports of Olympic marmot (Marmota olympus) disappearances from historically occupied locations suggested that the species might be declining. Concern was heightened by the precipitous decline of the Vancouver Island marmot (Marmota vancouverensis), coupled with reports that climate change was affecting other high-elevation species. However, it was unclear whether the Olympic marmot was declining or undergoing natural extinctions and recolonizations; distinguishing between normal metapopulation processes and population declines in naturally fragmented species can be difficult. From 2002-2006, we used multiple approaches to evaluate the population status of the Olympic marmot. We surveyed sites for which there were records indicating regular occupancy in the later half of the 20th century and we conducted range-wide surveys of open high-elevation habitat to establish current and recent distribution. We used these targeted and general habitat surveys to identify locations and regions that have undergone extinctions or colonizations in the past 1-4 decades. Simultaneously, we conducted detailed demographic studies, using marked and radio-tagged marmots, to estimate the observed and projected current population growth rate at nine locations. The habitat surveys indicate that local extinctions have been wide-spread, while no recolonizations were detected. Abundance at most intensive study sites declined from 2002-2006 and the demographic data indicate that these local declines are ongoing. Adult female survival in particular is considerably lower than it was historically. The spatial pattern of the extinctions is inconsistent with observed metapopulation dynamics in other marmot species and, together with very low observed dispersal rates, indicates that population is not at equilibrium.     

Using iron metal rods to infer oxygen status in seasonally saturated soils

The oxygen status in soils is fundamental to a number of earth-science processes including biological, physical and chemical interactions. Since oxygen is time consuming and often difficult to measure in soils, this research explores the use of zero-valent iron rods as a means of estimating oxygen content in soils. Zero-valent iron rods (polished nails) were placed in three soil toposequences and the surface coatings formed by oxidation were compared to measured oxygen concentrations taken every three weeks for one year. When water was present in the soils, the oxygen was measured as dissolved oxygen and in drained conditions it was reported as percent. Coatings on iron metal rods inserted in the soil appear to correlate well with specific oxygen ranges. Rods in soils with O₂ concentrations below about 2 mg l^− 1 do not develop bright (7.5YR 4/4 to 5/8) oxide/oxyhydroxide coatings, but instead formed black (10YR 2/1–2) coatings. Rods in soils with O₂ concentrations between about 2% to 5% develop variegated bright (7.5YR 4/4 to 5/8) oxide/oxyhydroxide coatings indicating soil drainage and microsite differences in O₂ concentrations. Rods in soils with O₂ concentrations above about 5% with adequate moisture are almost completely coated with bright (7.5YR 4/4 to 5/8) iron oxide/oxyhydroxides. Mineralogy of oxide/oxyhydroxide coatings could not be established by XRD presumably due to the short-range order crystal structure of the metal oxide/oxyhydroxides. This method provides a simple and inexpensive means to qualitatively estimate the ranges of O₂ status in soils. This research may have implications in hydric soil determination, horticultural and agricultural applications, as well as, remediation techniques.     

Emergence of Edwardsiella piscicida in Farmed Channel ♀, Ictalurus punctatus × Blue ♂, Ictalurus furcatus,Hybrid Catfish Cultured in Mississippi

There is a trend toward the increased incidence and prevalence of Edwardsiella piscicida septicemia in US catfish aquaculture, particularly in channel ♀, Ictalurus punctatus, × blue ♂, I. furcatus, hybrid catfish. From 2013 to 2017, a total of 3242 disease case submissions were made to the Aquatic Research and Diagnostic Laboratory (ARDL) at the Thad Cochran National Warmwater Aquaculture Center in Stoneville, MS. Of these, 1400 (43.2%) were hybrids. E. piscicida was suspected in 138 (4.3%) of cases, the majority of which (89.1%) were from hybrid catfish. A molecular survey of these isolates confirmed the majority (92.0%) to be E. piscicida. Furthermore, cases of E. piscicida from hybrids submitted to the ARDL and the Aquatic Diagnostic Laboratory of the Mississippi State University College of Veterinary Medicine in Starkville, MS, were documented for gross lesions and histological analysis. Grossly, E. piscicida presents with small dermal ulcerations, a raised fluid‐filled cranial midline lesion that is frequently ulcerated, hemorrhage in the gills, exophthalmia, and abdominal distension. Internally, lesions include splenomegaly, straw‐colored ascites, renomegaly, and occasionally hemorrhagic intestines. Histopathological examination is in agreement with gross observations, and infected fish repeatedly demonstrate a mononuclear meningoencephalitis, hemorrhagic branchitis, splenitis, ulcerative dermatitis, granulomatous interstitial nephritis, and hepatitis coupled with a hemorrhagic enteritis.     

The effect of otic vehicle and concentration of dexamethasone on liver enzyme activities and adrenal function in small breed healthy dogs

Dexamethasone 0.1% in propylene glycol vehicle has been shown to cause adrenal suppression and increased liver enzyme concentrations in normal dogs. The objectives of this study were to determine if these effects are concentration or vehicle dependent and to evaluate a dexamethasone 0.01% solution. Twenty-one privately owned normal dogs were included in this double-blinded study. Chemistry panels and adrenocorticotropin hormone (ACTH) stimulation tests were performed on day 0 and 15. Dogs were randomly assigned treatment with dexamethasone 0.01% in saline, 0.1% in saline, or 0.1% in a commercial preparation (Tresaderm®: Merial, Duluth, GA, USA) in each ear twice daily for 2 weeks. Nineteen dogs completed the study. After 2 weeks of treatment, all dogs receiving dexamethasone 0.01% in saline had normal ACTH stimulation tests and liver enzyme values. In contrast, four of seven dogs (57.14%) receiving dexamethasone 0.1% in saline experienced adrenal suppression, and four of six dogs (66.67%) receiving Tresaderm® experienced adrenal suppression with three of those dogs (50%) experiencing marked adrenal suppression. No dogs receiving dexamethasone 0.1% in saline had increased liver enzyme concentration, while one of six dogs (16.67%) experienced a slight elevation in alkaline phosphatase. In conclusion, it appears that adrenal suppression caused by otic dexamethasone is concentration and perhaps vehicle dependent. Veterinarians who formulate dexamethasone 0.1% otic solutions should be cognizant of potential adrenal suppression similar to that seen with Tresaderm® although not to the same degree. Dexamethasone at 0.01% did not cause adrenal suppression or liver enzyme alterations after 2 weeks of treatment.     

Meningomyelitis in dogs: a retrospective review of 28 cases (1999 to 2007)

Objectives : To characterise dogs with meningomyelitis and to compare signalment, body temperature and vaccination status to a representative control group. Methods : Dogs with meningomyelitis were identified retrospectively. Signalment, history, vaccination status, body temperature, severity of neurological dysfunction (modified Frankel score), diagnostic procedures, aetiology, survival to discharge and long‐term survival were analysed. Results : Affected dogs were younger (P<0·05) and more frequently hound or toy breeds (P<0·05) when compared with controls. Hound and toy breed dogs less than or equal to three years of age had a 13 times higher odds of meningomyelitis compared with other breeds (P<0·001). General proprioceptive ataxia, limb paresis and paraspinal hyperaesthesia were the most common clinical signs. Meningomyelitis of unknown aetiology and granulomatous meningomyelitis were the most common diagnoses. The median time to death or continued follow‐up in dogs alive at discharge was 213 days. Meningomyelitis resulted in death or euthanasia in 14 of 28 dogs. Clinical signs improved or resolved in seven of 28 dogs. Clinical Significance : Meningomyelitis is a differential diagnosis for dogs with clinical signs of myelopathy. Young dogs and toy or hound breeds seem to be predisposed. Clinical signs of meningomyelitis improve or resolve in some dogs.     

Investigation into intraoral approach for nerve block injection at the mental foramen in the horse

Invasive dental procedures performed in the standing, sedated horse are facilitated by local and regional anaesthesia. The traditional transcutaneous approach to the mental foramen is used to desensitise the incisive region including the mandibular incisors, but is not well tolerated by many sedated patients. In this study, a new, intraoral needle insertion technique for nerve block at the mental foramen was investigated. In 15 equine cadaver heads and two live horses, computed tomography (CT) was used to verify Tuohy needle placement into each mental foramen using an intraoral technique. Varying volumes of contrast medium (3, 6, 10 mL) were injected into the mandibular canal with and without digital occlusion of the mental foramen. The distance of retrograde flow was measured. Additionally, measurements were taken to determine the position of the mental foramen within the interdental space. Correct placement of Tuohy needles and injection of contrast medium into the mandibular canal using an intraoral approach at the mental foramen was achieved in all injections. Retrograde flow of contrast medium was accomplished with all volumes, regardless of occlusion. Although not statistically significant, the 10 mL group appeared to have a greater distance of flow. The needle insertion technique described here appears to be a potential alternative to traditional transcutaneous approaches to mental nerve block for procedures involving the incisive region. In addition, it was found that 79% of the mandibular canals injected with 10 mL of contrast medium had retrograde flow to the position of PM4, suggesting this method may be a useful alternative technique for nerve block for the more rostrally located cheek teeth. The location of the mental foramen was consistently found in the distal third of the interdental space (approximately 60–80% of the distance between the distal aspect of the lateral corner incisor and the mesial aspect of the second premolar).