Development, preparation, and evaluation of a novel dotted lateral flow immunochromatographic kit for rapid diagnosis of dermatophytosis

Dermatophytosis is a widely spread contagious zoonotic disease, affecting both man (tinea) and animals (ringworm). This disease is caused by a group of closely related keratinophilic fungi known collectively as the dermatophytes group. Although the wide distribution of dermatophytosis cases throughout the whole world and its adverse clinical effect on human health, economical effect on productive animals, and pet animal welfare, there is no rapid accurate diagnostic tool for such disease. The current conducted study tries to accomplish the difficult equation by achieving an accurate, sensitive, specific, user-friendly, rapid, robust, device-less, deliverable to end-users, and economic cost for the development and production of diagnostic kits. Through the development of a rapid diagnostic kit based on immunochromatographic assay with three major affordable reproducible production stages; preliminary stage, developmental and standardization stage, and evaluation stage. Obtaining dermatophytes-specific polyclonal antibodies against criteria-based selected dermatophytes strains associating proper gold nanoparticle preparation, characterization, and conjugation, with proper loading of the different bio-reactants on the efficiently laminated and fabricated lateral flow strips were the main challenge and control points through the whole process. Also, as a result of examining 100 animal samples using the new kit, the κ coefficients of the kit with the direct microscopy while the kit with the culture were 0.44 and 0.76, respectively. Therefore, the newly designated and developed kit showed a very promising competitive diagnostic result within 5-7 min through easy-to-be-performed three steps.

Tinea Gladiatorum Detection With a Dermatophyte Test Strip

OBJECTIVE

Determine sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and concordance of diafactory hs-TP (DTS) to detect tinea gladiatorum using direct potassium hydroxide (KOH) microscopy as the reference standard.

DESIGN

Prospective, comparative study.

SETTING

Seventeen Minnesota high schools during the winter wrestling season.

PATIENTS

Seventy-one consecutive high school wrestlers identified with a suspicious rash during skin inspection.

INTERVENTIONS

Samples were obtained from each rash for both DTS and direct KOH microscopy.

MAIN OUTCOME MEASURES

Readings were recorded as positive or negative.

RESULTS

Direct KOH microscopy identified tinea gladiatorum in 35 of the 71 samples (46%). DTS sensitivity was 80% (95% confidence interval 63%-92%), and specificity was 82% (66%-92%). PPV was 85% (68%-95%), and NPV was 86% (72 %-91%). The DTS result was 83% concordant (72%-91%) with direct KOH microscopy.

CONCLUSIONS

Similar to rapid Covid antigen tests, DTS required brief, basic training to perform and gave onsite results in 5 to 30 minutes. Although DTS is not approved for use in the United States by the FDA, concordance compared with direct KOH microscopy in diagnosing tinea gladiatorum was similar to results reported for DTS-TU in tinea unguium and tinea pedis. Further study comparing DTS to a reference standard using PCR plus direct microscopy is warranted.

Diagnosing Onychomycosis: What's New?

An overview of the long-established methods of diagnosing onychomycosis (potassium hydroxide testing, fungal culture, and histopathological examination) is provided followed by an outline of other diagnostic methods currently in use or under development. These methods generally use one of two diagnostic techniques: visual identification of infection (fungal elements or onychomycosis signs) or organism identification (typing of fungal genus/species). Visual diagnosis (dermoscopy, optical coherence tomography, confocal microscopy, UV fluorescence excitation) provides clinical evidence of infection, but may be limited by lack of organism information when treatment decisions are needed. The organism identification methods (lateral flow techniques, polymerase chain reaction, MALDI-TOF mass spectroscopy and Raman spectroscopy) seek to provide faster and more reliable identification than standard fungal culture methods. Additionally, artificial intelligence methods are being applied to assist with visual identification, with good success. Despite being considered the 'gold standard' for diagnosis, clinicians are generally well aware that the established methods have many limitations for diagnosis. The new techniques seek to augment established methods, but also have advantages and disadvantages relative to their diagnostic use. It remains to be seen which of the newer methods will become more widely used for diagnosis of onychomycosis. Clinicians need to be aware of the limitations of diagnostic utility calculations as well, and look beyond the numbers to assess which techniques will provide the best options for patient assessment and management.

Dermatophytic onychia: Effectiveness of rapid immunochromatographic diagnostic testing directly on samples compared to culture

BACKGROUND

Until now, definite diagnosis of dermatophytic onychia has been made by taking a nail sample and placing it in culture. The result is usually obtained only after 2 to 3weeks. More recently, diagnosis within a few minutes after sampling has become possible thanks to an immunochromatography technique developed in Japan and now available in France: the Diafactory Tinea Unguium® test strip (Biosynex, France).

METHODS

Over a 12-month period, 80nail samples from 80patients giving rise to a positive fungal culture were included in the study. For each patient, part of the removed nail was stored at room temperature and an immunochromatographic test was retrospectively performed according to the supplier's instructions. A small fragment of nail (≥ 1mg) was mixed with a few drops of reagent in a tube for 1min and the test strip was then placed in the tube with the result being visible to the naked eye (control strip, positivity strip) after incubation for a few minutes.

RESULTS

Compared with the culture method used for 51 isolated dermatophytes (42 Trichophyton rubrum, 9 Trichophyton interdigitale), the sensitivity of the rapid test was 96.07% (49/51). For the 29other fungal cultures (10Fusarium sp., 3Scytalidium sp., 3Scopulariopsis brevicaulis,3Aspergillus sp., 1Alternaria sp., 3Candida albicans, 1Candida parapsilosis, 1Trichosporons sp., 1Rhodotorula sp., and 3Corynebacterium sp.), the specificity was 75.86% (22/29). False positives were mainly due to the genera Fusarium and Scopulariopsis (6 of 7false positives), which were the likely cause of onychomycosis.

DISCUSSION

This rapid test could be useful in limiting excessive clinical diagnosis of dermatophyte onychomycosis. The rapid test has several advantages: ease of application, speed of results, and good performance, which, together, could improve diagnostic certainty during the actual consultation, thus limiting prolonged unnecessary prescriptions of antifungal treatments, while waiting for the laboratory culture results (3weeks for a negative result).

Validation of a lateral flow immunochromatographic assay for tinea unguium diagnosis

Tinea unguium is a common nail disease caused by dermatophytes. Although direct potassium hydroxide (KOH) microscopy and fungal culture are considered the gold standard for diagnosing this disease, their accuracy is insufficient. A lateral flow immunochromatographic assay (LFIA) kit, using a monoclonal antibody against Trichophyton rubrum, was developed and its sensitivity was recently improved 50% in vitro relative to its earlier version. The present study aimed to validate the clinical utility of this improved LFIA kit for diagnosing tinea unguium in comparison with direct KOH microscopy. A similar trial was simultaneously performed using scale samples from patients with tinea pedis to determine the assay's diagnostic potential. Nail samples, approximately 2 mg in weight, were collected from 112 non-treated tinea unguium patients and 56 non-tinea unguium patients. Samples from 25 tinea pedis patients and 20 non-tinea pedis patients were also collected. The sensitivity and specificity of the LFIA kit for tinea unguium was 84.8% (95/112) (95% confidence interval [CI], 76.8-90.9) and 83.9% (47/56) (95% CI, 71.7-92.4), respectively. The inconsistency rate was 15.5% (26/168) (95% CI, 10.4-21.9). The sensitivity and specificity of the LFIA kit for tinea pedis was 84.0% (21/25) and 100.0% (20/20), respectively. These results suggest that for diagnosing tinea unguium, the LFIA kit is a useful supplement to, but not a replacement for, direct KOH microscopy. For definitive diagnosis of suspected cases, appropriate sampling, repeated examinations, and a combination of diagnostic techniques are essential.

Dermatophyte Antigen Kit

The dermatophyte antigen kit uses monoclonal antibodies that react with polysaccharides present in the dermatophyte cell wall to detect dermatophyte antigens in specimens based on the principle of immunochromatography. Clinical studies showed that the kit was very useful in the diagnosis of tinea unguium but not tinea pedis. The kit was therefore further developed as an in vitro diagnostic tool for tinea unguium and was approved by the Pharmaceuticals and Medical Devices Agency of Japan. The kit's extraction solution can extract antigens from nail specimens quickly and efficiently. When direct microscopy fails to detect fungal elements in a specimen of suspected tinea unguium, the kit can be used so that positive samples are re-examined by direct microscopy, in order to reduce the likelihood of false-negative detection. In addition, in settings where direct microscopy is unavailable, the kit can be used so that treatment for dermatophytes is withheld when results are negative. Such an approach can reduce both wasteful treatment and medical costs. It is important to note that the kit is used to complement conventional fungus testing methods and that direct microscopy must be used to confirm the final morphological diagnosis of the pathogenic fungal infection. Use of a combination of direct microscopy and this kit should improve the accuracy of diagnosis of tinea unguium.

Acral manifestations of fungal infections

Fungal infections, which are named according to the body site involved, can affect any skin area, the fingernails, or the toenails. Numerous fungal agents are responsible for both superficial and deep fungal diseases. Dermatophytes and Candida spp are the most common causative organisms on the surface of the hands, feet, and nails of patients with superficial fungal diseases; however, although deep fungal infections of the skin are less common compared with superficial fungal diseases, their incidence is increasing worldwide due to cross-border travel. Most superficial fungal diseases are diagnosed clinically, but sometimes direct microscopic examination with potassium hydroxide and fungal culture may be necessary for diagnosis, especially in patients suspected of having tinea incognito. In cases of superficial fungal infections except for onychomycosis and tinea incognito, topical treatments are usually sufficient and effective, but systemic treatments may be required in recalcitrant cases. Deep fungal diseases may resemble each other clinically; therefore, the organism must be identified with laboratory methods and should be treated for a long period. We review the most important clinical, diagnostic, and therapeutic aspects of fungal diseases. This paper covers fungal problems encountered both in hospitals and in general practice.

Production of an anti-dermatophyte monoclonal antibody and its application: immunochromatographic detection of dermatophytes

Tinea refers to superficial infection with one of three fungal genera-Microsporum, Epidermophyton, or Trichophyton-that are collectively known as dermatophytes. These infections are among the most common diseases worldwide and cause chronic morbidity. They are usually diagnosed by direct microscopy and fungal culture, which are burdensome to perform in the clinical setting. To supplement conventional methods, we developed a new method that employs an immunochromatography test for detection of dermatophyte infections. First, anti-Trichophyton monoclonal antibodies (mAb) were produced in mice using a Trichophyton allergen solution as an immunogen. The mAb specificity was assessed by immunostaining alcohol fixed slide cultures and formalin fixed paraffin-embedded microbial samples. Both alcohol- and formalin-fixed samples of all seven species of Trichophyton tested displayed positive immunostaining. Immunochromatography test strips were created using the anti-Trichophyton mAb. The efficiency of the test strip was assessed in patients diagnosed with tinea unguium and in healthy volunteers. Of the 20 patient nails tested, 19 tested positive and one tested negative, whereas of the 17 volunteer nails, only one tested positive. However, KOH microscopic examination of the volunteer nail that tested positive revealed the existence of Trichophyton hyphae. Although the number of nails assayed was small, since the assay had a sensitivity of 95.0% (19/20) and a specificity of 94.1% (16/17), the obtained results were considered to be promising. Thus, while further investigation with a greater number of samples is necessary, this method could potentially be employed as a new diagnostic tool for Trichophyton in the future.