Comparative pharmacokinetics of amikacin in Greyhound and Beagle dogs

The purpose of the study was to compare the pharmacokinetics of amikacin administered i.v., to Greyhound and Beagle dogs and determine amikacin pharmacokinetics administered subcutaneously to Greyhounds. Amikacin was administered i.v. at 10 mg/kg to six healthy Greyhounds and six healthy Beagles. The Greyhounds also received amikacin, 10 mg/kg s.c. Plasma was sampled at predetermined time points and amikacin concentrations determined by a fluorescence polarization immunoassay (FPIA).
The volume of distribution was significantly smaller in Greyhounds (mean = 176.5 mL/kg) compared to Beagles (234.0 mL/kg). The C ₀ and AUC were significantly larger in Greyhounds (86.03 μg/mL and 79.97 h·μg/mL) compared to Beagles (69.97 μg/mL and 50.04 h·μg/mL). The plasma clearance was significantly lower in Greyhounds (2.08 mL/min/kg) compared to Beagles (3.33 mL/min/kg). The fraction of the dose absorbed after s.c. administration to Greyhounds was 0.91, the mean absorption time was 0.87 h, and the mean maximum plasma concentration was 27.40 μg/mL at 0.64 h.
Significant differences in the pharmacokinetics of amikacin in Greyhounds indicate it should be administered at a lower dose compared to Beagles. The dose in Greyhounds to achieve a C _max: AUC  ≥ 8 for bacteria (with an MIC  ≤ 4 μg/mL) is 12 mg/kg q24 h compared to 22 mg/kg q24 in Beagles.     

The natural history of Anaplasma marginale

The intracellular pathogen Anaplasma marginale (Rickettsiales: Anaplasmataceae), described by Sir Arnold Theiler in 1910, is endemic worldwide in tropical and subtropical areas. Infection of cattle with A. marginale causes bovine anaplasmosis, a mild to severe hemolytic disease that results in considerable economic loss to both dairy and beef industries. Transmission of A. marginale to cattle occurs biologically by ticks and mechanically by biting flies and by blood-contaminated fomites. Both male ticks and cattle hosts become persistently infected with A. marginale and serve as reservoirs of infection. While erythrocytes are the major site of infection in cattle, A. marginale undergoes a complex developmental cycle in ticks that begins by infection of gut cells, and transmission to susceptible hosts occurs from salivary glands during feeding. Major surface proteins (MSPs) play a crucial role in the interaction of A. marginale with host cells, and include adhesion proteins and MSPs from multigene families that undergo antigenic change and selection in cattle, thus contributing to maintenance of persistent infections. Many geographic strains of A. marginale have been identified worldwide, which vary in genotype, antigenic composition, morphology and infectivity for ticks. Isolates of A. marginale may be maintained by independent transmission events and a mechanism of infection/exclusion in cattle and ticks. The increasing numbers of A. marginale genotypes identified in some geographic regions most likely resulted from intensive cattle movement. However, concurrent A. marginale strain infections in cattle was reported, but these strains were more distantly related. Phylogenetic studies of selected geographic isolates of A. marginale, using msp4 and msp1α, provided information about the biogeography and evolution of A. marginale, and msp1α genotypes appear to have evolved under positive selection pressure. Live and killed vaccines have been used for control of anaplasmosis and both types of vaccines have advantages and disadvantages. Vaccines have effectively prevented clinical anaplasmosis in cattle but have failed to block A. marginale infection. Vaccines are needed that can prevent clinical disease and, simultaneously, prevent infection in cattle and ticks, thus eliminating these hosts as reservoirs of infection. Advances in genomics, proteomics, immunology and biochemical and molecular technologies during the last decade have been applied to research on A. marginale and related organisms, and the recent development of a cell culture system for A. marginale has provided a format for studying the pathogen/tick interface. Recent advancements and new research methodologies should provide additional opportunities for development of new strategies for control and prevention of bovine anaplasmosis.     

Analysis of the gut contents of the needlefish,Hyporhamphus knysnaensis (Smith), from Rondevlei,southern cape

The gut contents of 313 specimens of Hyporhamphus knysnaensis from Rondevlei were analysed. The total lengths of the collected fish varied between 5,1 and 21,8 cm. It was found that the annual cycle in the occurrence of submerged macrophytes in Rondevlei appears to directly influence the feeding of H. knysnaensis of 9 to 17 cm long. This length- group fed mainly on animal material (mostly amphipods and isopods) in winter and the first half of spring while submerged macrophytes were scarce. After the submerged macrophytes became more abundant, however, the 9 to 17-cm length-group changed to a predominantly plant diet (consisting of Ruppia spiralis and Potamogeton pectinatus). H. knysnaensis between approximately 5 and 9 cm long appeared in summer and fed mainly on animal material (mostly amphipods and isopods). Of the 47 specimens collected in this length-group between December 1978 and March 1979, all had animal material in their gut contents. It was the dominant food in 94% of the specimens and formed 90% of the gut contents. In general, therefore, H. knysnaensis can be considered an omnivore.     

Understanding Ebola virus and other zoonotic transmission risks through human–bat contacts: Exploratory study on knowledge,attitudes and practices in Southern Cameroon

The ecology of Ebola virus (EBV) remains largely unknown, but the previous detection of viral RNA and anti‐EBV antibodies in African bats suggests that they might play a role in the EBV reservoir. Moreover, African bats also carry other potentially zoonotic agents such as Henipah‐like viruses, coronaviruses and lyssaviruses. Today only little information is available on interactions between humans and bats. The objective of our exploratory study was to describe the extent and modes of contacts between humans and bats in southern Cameroon, considered as an area at risk for future EBV outbreaks. The survey was conducted in 11 villages of four distinct rural areas in southern Cameroon. A total of 135 respondents were interviewed using semi‐structured questionnaires, between February and May 2017. The study showed that direct contacts between bats and humans are relatively common. Bat bushmeat appeared to be an occasional meat resource; 40% of respondents consume bats with a median annual consumption of three, and 28% of respondents hunt them. About 22% of the respondents reported children catching bats. Indirect contact also appeared to be common; 55% of hunters use caves as shelters and 67% of interviewees eat fruits previously chewed by bats. Bat consumption varied significantly between regions (from 0% to 87%) and between pygmies and bantus in the extreme south‐east of Cameroon. The study revealed considerable diversity in practices among interviewees, most of them being subsistence cultivators and relying on self‐hunted bushmeat. Geographical diversity of contacts and perceptions regarding bats in Cameroon emphasizes the need to adjust zoonotic pathogen surveillance and education campaigns to the specificities of the communities and their context of interaction with wildlife.     

Flow cytometric evaluation of selected antimicrobial efficacy for clearance of Anaplasma marginale in short-term erythrocyte cultures

The tick-borne rickettsia, Anaplasma marginale, causes the economically important cattle disease anaplasmosis. Once infected, cattle remain lifelong carriers. Herein, we used flow cytometry to test the efficacy of three antimicrobials; oxytetracycline, imidocarb and enrofloxacin against Virginia (VGN) or Oklahoma (OK) A. marginale isolates in short-term erythrocyte cultures. Parasite viability was assessed using the vital dye hydroethidine (HE), which is detectable when living organisms convert HE to ethidium bromide. Viability of A. marginale in selected cultures was determined by subinoculation into susceptible calves. Data were analyzed by MANOVA, Tukey-Kramer honest significant difference and Wilcoxon rank sum tests. Receiver operating characteristic (ROC) analysis was used to correlate results with culture infectivity. Enrofloxacin inhibited A. marginale in a dose dependent manner. Surprisingly, higher concentrations of imidocarb were less effective than lower concentrations against A. marginale with significant differences (P < 0.05) observed between the two isolates. Oxytetracycline was the least active drug tested. Cultures infected with the OK isolate exposed to 4.0 microg/mL enrofloxacin and those of the VGN and OK isolates exposed to 1.0 microg/mL imidocarb were sterilized. This is the first in vitro study demonstrating the efficacy of enrofloxacin against A. marginale. Furthermore, these data indicate that flow cytometry is a useful assay for screening antimicrobials against A. marginale.     

Contribution of Fimbrial and Afimbrial Adhesins of Xylella fastidiosa to Attachment to Surfaces and Virulence to Grape

ABSTRACT The role of fimbrial and afimbrial adhesins of Xylella fastidiosa in biofilm formation was assessed by visualization of cell aggregates of mutant strains after incubation on glass surfaces. FimA- or FimF- fimbrial mutants adhered as solitary cells at a slightly lesser frequency to glass surfaces than the parental strain; however, cell aggregates were not formed, unlike the wild-type strain. Conversely, whereas the XadA- and HxfB- nonfimbrial mutants also exhibited a much lower frequency of adherence to glass surfaces than the wild-type strain, most of the cells retained on the surfaces were in cell aggregates of different sizes, much like that of the parental strain. Neither fimbrial or afimbrial mutants formed a mature biofilm on the sides of flasks of broth cultures, unlike the dense biofilm formed by the wild-type strain. Although FimA- and FimF- mutants did not form cell aggregates on glass surfaces when incubated as individual strains, aggregates of a FimA- or FimF- mutant were observed when co-incubated with either a XadA- mutant or HxfB- mutant, respectively. These results are consistent with a model in which the fimbrial adhesins FimA and FimF are involved preferentially in cell-to-cell aggregate formation whereas the afimbrial adhesions XadA and HxfB preferentially contribute to initial cell binding to surfaces, whereupon further cell aggregation can occur. In each of five separate experiments, FimA, FimF, XadA, and HxfB mutants of X. fastidiosa all were less virulent to grape than the corresponding wild-type strain. Fimbrial and afimbrial mutants might produce a reduced biofilm within vessels of grape and, hence, be deficient in various cell-density-dependent traits required for movement through the plant and, thus, virulence.     

Armillaria root rot spreading into a natural woody ecosystem in South Africa

Signs and symptoms of a disease similar to those of armillaria root rot have recently been observed on various native woody plants on the foothills of Table Mountain in South Africa, one of the most botanically diverse natural environments globally. This is of concern because the root rot fungus Armillaria mellea has previously been shown to be an alien pathogen of European origin in planted gardens in the City of Cape Town. An aim of this study was to identify the cause of the root rot disease on infected plants. Based on DNA‐sequence phylogeny, it was shown that isolates collected from at least 16 native tree and woody shrub species represented the non‐native A. mellea. Microsatellite markers were then used to determine the genetic diversity and population structure of the A. mellea isolates from Table Mountain and two planted gardens where the pathogen has previously been found. Population genetic analyses revealed low levels of gene diversity and no population differentiation amongst the three populations. The results provide the first firm evidence that A. mellea has escaped the planted environment and invaded a sensitive and ecologically important natural woody environment in South Africa. This is only the second definitive case of a non‐native tree pathogen invading a natural ecosystem in the country.     

Vaccination mitigates the impact of PRRSv infection on the pharmacokinetics of ceftiofur crystalline‐free acid in pigs

The pharmacokinetics of intramuscularly administered ceftiofur crystalline‐free acid (CCFA) were determined in pigs that were clinically healthy (n = 8), vaccinated with a Porcine reproductive and respiratory syndrome modified live virus (PRRS MLV) (n = 10), challenged with wild‐type porcine reproductive and respiratory syndrome virus (PRRSv) VR‐2385 (n = 10), or vaccinated with PRRS MLV and later challenged with wild‐type PRRSv VR‐2385 (n = 10). Animals were given a single dose of CCFA intramuscularly at 5 mg/kg body weight. Blood was collected at 0 (pretreatment), 0.25, 0.5, 1, 6, 12, 24, 48, 96, 144, 192, and 240 h postinjection. Plasma was analyzed using liquid chromatography‐mass spectrometry. Plasma concentration–time curves for each group were evaluated with noncompartmental modeling. When compared to control animals, those receiving the PRRSv wild‐type challenge only had a lower AUC_0‐last, higher Cl/F, and higher Vz/F. The PRRSv wild‐type challenge only group had the longest T_1/2λ. The C_max did not differ among all four treatments. Control animals had no statistically significant differences from animals vaccinated with PRRS MLV alone or animals vaccinated with PRRS MLV and later challenged with wild‐type PRRSv. Our results suggest that PRRSv wild‐type infection has the potential to alter CCFA pharmacokinetics and PRRS MLV vaccination may attenuate those changes.     

Pharmacokinetics and tissue disposition of meloxicam in beef calves after repeated oral administration

The objective of this study was to investigate the pharmacokinetics and tissue disposition of meloxicam after repeated oral administration in calves. Thirteen male British × Continental beef calves aged 4 to 6 months and weighing 297–392 kg received 0.5 mg/kg meloxicam per os once daily for 4 days. Plasma meloxicam concentrations were determined in 8 calves over 6 days after first treatment. Calves were randomly assigned to be euthanized at 5, 10, 15 (n = 3/timepoint), and 19 days (n = 4) after final administration. Meloxicam concentrations were determined in plasma (LOQ= 0.025 μg/mL) and muscle, liver, kidney, and fat samples (LOQ = 2 ng/g) after extraction using validated LC–MS–MS methods. The mean (± SD) C_max, C_min, and C_average plasma meloxicam concentrations were 4.52 ± 0.87 μg/mL, 2.95 ± 0.77 μg/mL, and 3.84 ± 0.81 μg/mL, respectively. Mean (± SD) tissue meloxicam concentrations were highest in liver (226.67 ± 118.16 ng/g) and kidney samples (52.73 ± 39.01 ng/g) at 5 days after final treatment. Meloxicam concentrations were below the LOQ in all tissues at 15 days after treatment. These findings suggest that tissue from meloxicam‐treated calves will have low residue concentrations by 21 days after repeated oral administration.