Perspectives and Possibilities for New Antimicrobial Agents in the Treatment and Control of Mastitis Induced by Algae of the Genus Prototheca spp.: A Review

Innovative approaches in nanotechnology provide a potentially promising alternative to untreatable cases of mastitis caused by genus Prototheca spp. algae infections. Drying of the teats of the affected animals or culling are typically the outcomes of mastitis in dairy cattle caused by these pathogens. A major issue in both veterinary medicine and animal breeding is the Prototheca species' widespread resistance to the current methods of managing infections and the available drugs, including antibiotics. Commercial antifungal preparations are also ineffective. Nanotechnology, an emerging discipline, has the potential to create an effective alternative treatment for protothecal mastitis. The aim of the paper is to combine the literature data on the use of nanotechnology in the control of mastitis, taking into account data on combating mastitis caused by Prototheca spp. infections. The databases employed were PubMed, Google Scholar, and Scopus, focusing on literature from the last 20 years to ensure relevance and currency. Studies conducted in vitro have demonstrated that nanomaterials have significant biocidal activity against mastitis infections of different etiologies. Analyzed research papers show that (NPs), such as AgNPs, CuNPs, AuNPs, etc., may not negatively impact various cell lines and may be effective agents in reducing the pathogens' viability. However, it is also critical to assess the risks involved in using nanomaterials.

Updates on antifungal pharmacotherapy in elasmobranchs: pharmacokinetics of 4 mg/kg voriconazole after IM and IV administration in undulate skates (Raja undulata) maintained under human care

Introduction

Fungal diseases are frequently associated with elevated mortality rates in elasmobranchs. Currently, there is a notable absence of scientifically validated therapeutic medications that can ensure both effectiveness and safety when administered to this group of animals. The empirical prescription of azole antifungal agents, particularly voriconazole, has been posited as a potentially efficacious treatment approach for addressing most common mycoses in sharks and rays. However, there are still no published pharmacokinetic studies supporting its use in elasmobranchs and there is a lack of scientific base for its utilization in elasmobranchs.

Methods

For this study, voriconazole was administered intravenously (IV) and intramuscularly (IM), at a single dose of 4 mg/kg to six adult undulate skates (Raja undulata). A washout period of 8 weeks was left between each route of administration. Blood samples were collected both before and at ten predetermined intervals after each dosing (0.25, 0.5, 1, 1.5, 2, 4, 8, 12, 24, and 36 h after drug administration). Plasma concentrations were quantified using a validated high-performance liquid chromatography method, and pharmacokinetic (PK) data was analyzed through non-compartmental methods.

Results

The mean extrapolated concentration at 0 h (C0) after IV administration was 27.19 ± 7.15 μg/mL and the mean peak plasma concentrations (Cmax) ± SEM after IM administration resulted 2.98 ± 0.28 μg/mL at a mean time to maximum concentration (T max) of 1.33 ± 0.17 h. Terminal half-lives were calculated and resulted 11.18 ± 1.32 h for IV injections and 9.59 ± 1.38 h for IM injections. The area under the curve extrapolated to infinity was determined as 58.14 ± 2.79 h·μg/ml following IV injections and 37.60 ± 6.67 h·μg/ml following IM injections. The IM-administered voriconazole exhibited a mean absolute bioavailability of 64.67 ± 11.47%.

Discussion

These discoveries provide backing for the possible application of voriconazole through the intramuscular route in undulate skates and support using lower dosage regimens compared to those required for oral administration, emphasizing the importance of conducting further pharmacokinetic studies with antifungals in elasmobranchs.

Invasive fungal infections and oomycoses in cats 2. Antifungal therapy

CLINICAL RELEVANCE

Invasive fungal infections (IFIs) and oomycoses (hereafter termed invasive fungal-like infections [IFLIs]) are characterised by penetration of tissues by fungal elements. The environment is the most common reservoir of infection. IFIs and IFLIs can be frustrating to treat because long treatment times are usually required and, even after attaining clinical cure, there may be a risk of relapse. Owner compliance with medication administration and recheck examinations can also decline over time. In addition, some antifungal drugs are expensive, have variable interpatient pharmacokinetic properties, can only be administered parenterally and/or have common adverse effects (AEs). Despite these limitations, treatment can be very rewarding, especially when an otherwise progressive and fatal disease is cured.

AIM

In the second of a two-part article series, the spectrum of activity, mechanisms of action, pharmacokinetic and pharmacodynamic properties, and AEs of antifungal drugs are reviewed, and the treatment and prognosis of specific IFIs/IFLIs - dermatophytic pseudomycetoma, cryptococcosis, sino-orbital aspergillosis, coccidioidomycosis, histoplasmosis, sporotrichosis, phaeohyphomycosis, mucormycosis and oomycosis - are discussed. Part 1 reviewed the diagnostic approach to IFIs and IFLIs.

EVIDENCE BASE

Information on antifungal drugs is drawn from pharmacokinetic studies in cats. Where such studies have not been performed, data from 'preclinical' animals (non-human studies) and human studies are reviewed. The review also draws on the wider published evidence and the authors' combined expertise in feline medicine, mycology, dermatology, clinical pathology and anatomical pathology.

ABBREVIATIONS FOR ANTIFUNGAL DRUGS

AMB (amphotericin B); FC (flucytosine); FCZ (fluconazole); ISA (isavuconazole); ITZ (itraconazole); KCZ (ketoconazole); PCZ (posaconazole); TRB (terbinafine); VCZ (voriconazole).

Fungal Diseases in Elasmobranchs and Their Possible Treatment with a Special Mention to Azole Antifungal Agents

INTRODUCTION

Elasmobranchs currently constitute an important part of the animal collection of many aquariums worldwide. Their maintenance under human care has allowed us to describe and identify new pathogens and diseases affecting them, as well as to determine different treatments for these diseases. Great advances in elasmobranch husbandry have been developed.

METHODS

A search was performed on scientific databases as PubMed and other specialized sources (IAAAM archive).

RESULTS

Little information on pharmacotherapeutics is available in this taxonomic group, and treatments lack a scientific base and instead are frequently dependent on empirical knowledge. Pharmacokinetic studies are the first step to determining therapeutic protocols that are safe and effective. The available bibliography shows that a majority of the mycoses recorded in cartilaginous fish are severe, aggravated by the fact that the antifungal treatments administered, following the guidelines used for teleost species, are ineffective in elasmobranchs. Azoles appear to be a promising group of antifungals for use in treating systemic mycoses in sharks and rays.

CONCLUSIONS

Based on the findings of this review, it is essential to investigate the pharmacokinetics of the different antifungals in these species in order to provide therapeutic options for fungal infections in cartilaginous fish.

Antifungal susceptibility profile of yeasts isolated from the oral cavity of cats

BACKGROUND

Microorganisms living in the oral cavity play an important role in health and disease of the host. Cats are susceptible to oral infections, and it is documented that fungi in the oral cavity could impact these infections. Antifungal resistance has been increasing in recent years.

OBJECTIVES

This study was designed to identify yeast isolates from the oral cavity of healthy cats and to evaluate their antifungal susceptibility pattern.

METHODS

Oral specimens were collected from 60 cats and cultured at 37°C for 10 days. Yeasts were isolated and identified. Their antifungal susceptibility pattern was determined according to CLSI M44-A.

RESULTS

Three yeast genera were isolated, including Candida spp (55.5%), Rhodotorula spp (33.3%) and Hanseniaspora spp (11.1%). Antifungal susceptibility profiling showed that, apart from a dose-dependent effect of itraconazole, Hanseniaspora spp was susceptible to all seven drugs studied. The Candida species were susceptible to all drugs except ketoconazole (sensitivity 80%) and caspofungin (sensitivity 40%). In R. glutinis and R. minuta, 100% sensitivity was observed for amphotericin B, posaconazole, ketoconazole and voriconazole.

CONCLUSIONS

The results suggest that, in comparison with humans and other animals, cats have a different oral mycoflora in terms of species, number and diversity. However, these isolates have similar susceptibility patterns to those seen in isolates from other animals and humans. More studies should be done to further characterize the oral mycobiota of cats and its role in oral infections.

Clinical utility of fungal culture and antifungal susceptibility in cats and dogs with histoplasmosis

BACKGROUND

Culture can be used for diagnosis and antifungal susceptibility testing in animals with fungal infections. Limited information is available regarding the diagnostic performance of culture and the susceptibility patterns of Histoplasma spp. isolates.

HYPOTHESIS/OBJECTIVES

Describe the clinical utility of culture and the susceptibility patterns of Histoplasma spp. isolates causing histoplasmosis in cats and dogs.

ANIMALS

Seventy-one client-owned animals, including 33 cats and 19 dogs with proven or probable histoplasmosis.

METHODS

Culture was attempted from tissue or fluid samples. Diagnostic performance of culture, cytopathology, and antigen detection were compared with final diagnosis. Susceptibility to antifungal agents was determined for a subset (11 from dogs, 9 from cats) of culture isolates.

RESULTS

Culture had a diagnostic sensitivity of 17/33 (52%; 95% confidence interval [CI], 34%-69%) and 15/19 (79%; 95% CI, 61%-97%) and specificity of 6/6 (100%; 95% CI, 54%-100%) and 10/10 (100%; 95% CI, 69%-100%) in cats and dogs, respectively. Culture was not positive in any animal in which cytopathology and antigen testing were negative. Target drug exposure (area under the concentration curve [AUC]/minimum inhibitory concentration [MIC] >25) should be easily achieved for all isolates for itraconazole, voriconazole, or posaconazole. Five of 20 (25%) isolates had fluconazole MIC ≥32 μg/mL and achieving target drug exposure is unlikely.

CONCLUSIONS AND CLINICAL IMPORTANCE

Fungal culture did not improve diagnostic sensitivity when used with cytopathology and antigen detection. Susceptibility testing might help identify isolates for which fluconazole is less likely to be effective.

Pharmacokinetics of isavuconazole in healthy cats after oral and intravenous administration

Background

Isavuconazole is a triazole antifungal drug that has shown good efficacy in human patients. Absorption and pharmacokinetics have not been evaluated in cats.

Objectives

To determine the pharmacokinetics of isavuconazole in cats given a single IV or PO dose.

Animals

Eight healthy, adult research cats.

Methods

Four cats received 100 mg capsules of isavuconazole PO. Four cats received 5 mg/kg isavuconazole solution IV. Serum was collected at predetermined intervals for analysis using ultra‐high performance liquid chromatography‐tandem mass spectrometry. Data were analyzed using a 2‐compartment uniform weighting pharmacokinetic analysis with lag time for PO administration and a 2 compartment, 1/y² weighting for IV administration. Predicted 24 and 48‐hour dosing intervals of 100 mg isavuconazole administered PO were modeled and in vitro plasma protein binding was assessed.

Results

Both PO and IV drug administration resulted in high serum concentrations. Intravenous and PO formulations of isavuconazole appear to be able to be used interchangeably. Peak serum isavuconazole concentrations occurred 5 ± 3.8 hours after PO administration with an elimination rate half‐life of 66.2 ± 55.3 hours. Intersubject variability was apparent in both the PO and IV groups. Two cats vomited 6 to 8 hours after PO administration. No adverse effects were observed in the IV group. Oral bioavailability was estimated to be approximately 88%. Serum protein binding was calculated to be approximately 99.0% ± 0.03%.

Conclusions and Clinical Importance

Isavuconazole might prove to be useful in cats with fungal disease given its favorable pharmacokinetics. Additional studies on safety, efficacy, and tolerability of long‐term isavuconazole use are needed.

Utility of systemic voriconazole in equine keratomycosis based on pharmacokinetic-pharmacodynamic analysis of tear fluid following oral administration

Objective

To clarify the detailed pharmacokinetics (PK) of orally administered voriconazole in tear fluid (TF) of horses for evaluating the efficacy of voriconazole secreted into TF against equine keratomycosis.

Animals studied

Five healthy Thoroughbred horses.

Procedures

Voriconazole was administrated through a nasogastric tube to each horse at a single dose of 4.0 mg/kg. TF and blood samples were collected before and periodically throughout the 24 hours after administration. Voriconazole concentrations in plasma and TF samples were analyzed using liquid chromatography‐electrospray tandem‐mass spectrometry. The predicted voriconazole concentration in both samples following multiple dosing every 24 hours was simulated by the superposition principle.

Results

The mean maximum voriconazole concentrations in plasma and TF were 3.3 μg/mL at 1.5 h and 1.9 μg/mL at 1.6 h, respectively. Mean half‐life in both samples were 16.4 and 25.2 h, respectively. The ratio of predicted AUC_0–24 at steady state in TF (51.3 μg∙h/mL) to previously published minimum inhibitory concentration (MIC) of Aspergillus and Fusarium species was >100 and 25.7, respectively.

Conclusions

This study demonstrated the detailed single‐dose PK of voriconazole in TF after oral administration and simulated the predicted concentration curves in a multiple oral dosing. Based on the analyses of PK‐PD, the simulation results indicated that repeated oral administration of voriconazole at 4.0 mg/kg/d achieves the ratio of AUC to MIC associated with treatment efficacy against Aspergillus species. The detailed PK‐PD analyses against pathogenic fungi in TF can be used to provide evidence‐based medicine for equine keratomycosis.

Fungal Rhinosinusitis and Disseminated Invasive Aspergillosis in Cats

Fungal rhinosinusitis, including sinonasal aspergillosis (SNA) and sino-orbital aspergillosis (SOA), is the most common type of aspergillosis encountered in cats. Other focal forms of aspergillosis including disseminated invasive aspergillosis occur less frequently. SOA is an invasive mycosis that is increasingly recognized and is most commonly caused by Aspergillus felis, a close relative of Aspergillus fumigatus. SNA can be invasive or noninvasive and is most commonly caused by A fumigatus and Aspergillus niger. Molecular methods are required to correctly identify the fungi that cause SNA and SOA. SNA has a favorable prognosis with treatment, whereas the prognosis for SOA remains poor.

Opportunistic Fungal Infections in Small Animals

Opportunistic fungal infections have long been recognized as rare causes of disease in immunocompetent dogs and cats. Recently, the escalating use of multiagent immunosuppression protocols (especially those that include cyclosporine) has resulted in an increased number of patients with opportunistic fungal infection encountered by small animal practitioners and has altered the typical case phenotype. Based on histologic and cytologic features such as pigmentation, hyphal diameter, and distribution in tissue, these opportunistic mycoses can be placed into categories such as phaeohyphomycosis, hyalohyphomycosis, and eumycotic mycetoma. This review aims to summarize the clinical presentations, methods for diagnosis, treatment recommendations, and prognosis for both immunocompetent and immunosuppressed patients with opportunistic fungal infections. An example case description is included to illustrate the most common current clinical presentation.