Seroprevalence of antibodies against Coccidioides immitis in healthy horses

Development of a rapid lateral flow assay for detection of anti-coccidioidal antibodies

Coccidioides spp. are dimorphic fungi that are capable of infecting human and non-human mammals and can cause diverse manifestations of coccidioidomycosis or Valley fever (VF). In combination with clinical symptoms and radiographic findings, antibody-based diagnostic tests are often used to diagnose and monitor patients with VF. Chitinase 1 (CTS1) has previously been identified as the seroreactive antigen used in these diagnostic assays to detect anticoccidial IgG. Here, an indirect enzyme-linked immunosorbent assay to detect IgG to CTS1 demonstrated 165 of 178 (92.7%) patients with a positive result by immunodiffusion (ID) and/or complement fixation (CF) had antibodies to the single antigen CTS1. We then developed a rapid antibody lateral flow assay (LFA) to detect anti-CTS1 antibodies. Out of 143 samples tested, the LFA showed 92.9% positive percent agreement [95% confidence interval (CI), 84.3%-96.9%] and 97.7% negative percent agreement (95% CI, 87.9%-99.6%) with ID and CF assays. Serum or plasma from canines, macaques, and dolphins was also tested by the CTS1 LFA. Test line densities of the CTS1 LFA correlated in a linear manner with the reported CF and ID titers for human and non-human samples, respectively. This 10-min point-of-care test for the rapid detection of anti-coccidioidal antibodies could help to inform healthcare providers in real-time, potentially improving the efficiency of healthcare delivery.

Coccidioidomycosis in 26 horses in California, USA: case series and review of the literature

Coccidioidomycosis is a fungal disease caused by Coccidioides immitis or Coccidioides posadasii. We searched the records of the California Animal Health and Food Safety Laboratory from 1990 through 2020 for cases of coccidioidomycosis in horses. The selection criteria for these cases were: 1) live-born horses submitted for autopsy, and 2) a diagnosis of coccidioidomycosis was established, regardless of cause of death. During that time, 19,054 horses were received, and 26 cases (0.14%) of coccidioidomycosis were diagnosed in horses, of which 19 (73%) cases had pneumonia and/or pleuritis with or without lesions in other organs, and 7 (27%) cases had lesions only in organs other than the lungs (nasal mucosa, spleen, thoracic lymph nodes, heart, pericardial sac, liver, kidney, mediastinum, and/or mesentery). Pneumonia was diagnosed as the cause of death in 1,838 (9.64%) of the horses received; Coccidioides spp. was the cause of pneumonia in 19 (1.0%) of these animals. Horses have been reported to have low susceptibility to coccidioidomycosis, and the severity and chronicity of the disease can be variable. Lesions in our cases consisted of multifocal-to-coalescing pyogranulomas with intralesional fungal spherules. Coccidioidomycosis must be considered a differential diagnosis in cases of persistent cough, chronic weight loss, fever, and cases with a travel history to, or living in, a region considered endemic for coccidioidomycosis. Coccidioides spp. infection should also be considered when pyogranulomatous inflammation is found within lung, spleen, nasal mucosa, and lymph nodes of horses.

Coccidioidomycosis in llamas and alpacas diagnosed at the University of California, Davis (1990-2016)

Given the predisposition of South American camelids to coccidioidomycosis, we sought to describe the disease presentation in alpacas and llamas and identify potential risk factors for these species. The records of 224 llamas and alpacas that were tested for Coccidioides infection using immunodiffusion serology at the Coccidioidomycosis Serology Laboratory of the University of California, Davis, between 1990 and 2016 were examined; of those, 46 alpacas and 42 llamas had positive test results. The remaining 99 alpacas and 37 llamas were used as control groups. We found that male llamas were at increased risk for Coccidioides infection when compared with female llamas and when compared with male alpacas. South American camelids living within California were at higher risk for infection than camelids living in other states. Alpacas were more likely than llamas to have subclinical infections. We documented five cases of abortion or neonatal mortality attributable to coccidioidomycosis in alpacas. Our study demonstrates that South American camelids are susceptible to Coccidioides infection in areas where the disease is endemic, lending support to the importance of vigilance for this disease in alpacas and llamas and suggesting a possible role for these animals as sentinel species.

LAY SUMMARY

We examined cases of Valley Fever and described the disease and risk factors for llamas and alpacas. Male llamas were at increased risk for infection as were animals living within California. Five alpacas had miscarriages or neonatal deaths as a result of Valley Fever infections.

Development of an enzyme immunoassay for detection of antibodies against Coccidioides in dogs and other mammalian species

Coccidioides is a soil-dwelling fungus that causes coccidioidomycosis, a disease also known as Valley fever, which affects humans and a variety of animal species. Recent findings of Coccidioides in new, unexpected areas of the United States have demonstrated the need for a better understanding of its geographic distribution. Large serological studies on animals could provide important information on the geographic distribution of this pathogen. To facilitate such studies, we used protein A/G, a recombinant protein that binds IgG antibodies from a variety of mammalian species, to develop an enzyme immunoassay (EIA) that detects IgG antibodies against Coccidioides in a highly sensitive and high-throughput manner. We showed the potential of this assay to be adapted to multiple animal species by testing a collection of serum and/or plasma samples from dogs, mice, and humans with or without confirmed coccidioidomycosis. We then evaluated the performance of the assay in dogs, using sera from dogs residing in a highly endemic area, and found seropositivity rates significantly higher than those in dogs of non-endemic areas. We further evaluated the specificity of the assay in dogs infected with other fungal pathogens known to cross-react with Coccidioides. Finally, we used the assay to perform a cross-sectional serosurvey investigating dogs from Washington, a state in which infection with Coccidioides has recently been documented. In summary, we have developed a Coccidioides EIA for the detection of antibodies in canines that is more sensitive and has higher throughput than currently available methods, and by testing this assay in mice and humans, we have shown a proof of principle of its adaptability for other animal species.

Update on fungal respiratory disease in horses

Fungal respiratory disease is a rare occurrence in horses. Fungal organisms are ubiquitous in the equine environment; however, there is a geographic predisposition for disease development, with fungal respiratory infections seen more commonly by practitioners working in tropical or subtropical environments. Diagnosis and treatment of fungal respiratory infections pose a challenge for the equine practitioner, and the prognosis for complete resolution of infection is often guarded; however, new antifungal medications are likely to improve treatment success. This article summarizes the available literature regarding the cause, diagnosis, and treatment of equine fungal respiratory disease.

Fungal diseases of horses

Among diseases of horses caused by fungi (=mycoses), dermatophytosis, cryptococcosis and aspergillosis are of particular concern, due their worldwide diffusion and, for some of them, zoonotic potential. Conversely, other mycoses such as subcutaneous (i.e., pythiosis and mycetoma) or deep mycoses (i.e., blastomycosis and coccidioidomycosis) are rare, and/or limited to restricted geographical areas. Generally, subcutaneous and deep mycoses are chronic and progressive diseases; clinical signs include extensive, painful lesions (not pathognomonic), which resemble to other microbial infections. In all cases, early diagnosis is crucial in order to achieve a favorable prognosis. Knowledge of the epidemiology, clinical signs, and diagnosis of fungal diseases is essential for the establishment of effective therapeutic strategies. This article reviews the clinical manifestations, diagnosis and therapeutic protocols of equine fungal infections as a support to early diagnosis and application of targeted therapeutic and control strategies.

[Endemic fungal pathogens in a rural setting of Argentina: seroepidemiological study in dogs]

BACKGROUND

Three fungal species causing human disease, namely Paracoccidioides brasiliensis, Histoplasma capsulatum and Coccidioides sp., are endemic in different areas of Argentina. Rates of infection in domestic dogs have been used in other Latin American countries as indicators of the presence of these pathogens in a given area. We used such an approach to investigate the epidemiological relevance of paracoccidiodomycosis, histoplasmosis and coccidioidomycosis in our country.

AIM

To investigate the presence of P. brasiliensis, H. capsulatum and Coccidioides sp. in a rural area of Argentina called Interfluvio Teuco-Bermejito, located in Chaco province.

METHODS

We applied Western Blotting to determine the presence of specific antibodies in sera from 89 domestic dogs inhabiting the area. Antibodies against the following extra-cellular fungal antigens were investigated: gP43 of P. brasiliensis, H/M of H. capsulatum and 120, 82 and 48kDa antigen bands of Coccidioides sp.

RESULTS

Specific antibodies against H. capsulatum were found in 9/89 (10%) sera: 8 reacted against both H and M antigens and 1 only reacted against antigen M. Of these 9 sera, one showed additional anti-gp43 activity and another reacted against all the fungal antigens tested.

CONCLUSIONS

This is the first study using dog infection to assess the presence of endemic fungal pathogens in Argentina. Our results suggest that H. capsulatum is the main dimorphic fungal pathogen in the Interfluvio Teuco-Bermejito area. Therefore, the diagnosis of histoplasmosis should be taken into account in patients living in this geographic region who show pulmonary or mucocutaneous symptoms compatible with the disease.

Comparison of Coccidioides immitis serological antibody titres between forms of clinical coccidioidomycosis in horses

A retrospective study was performed to determine if there is an association between serological Coccidioides immitis antibody titres (IgG) and form/severity of coccidioidal disease in horses, and to identify trends in survival and treatment success based on the form of the disease. Data were obtained on horses with positive serological titres tested at the Coccidioidomycosis Serology Laboratory, School of Medicine, University of California, Davis from 1981 to 2004. Thirty-nine cases in which a diagnosis of coccidioidomycosis had been made were selected for inclusion. Six distinct categories were identified including abortion (n=6), miliary/interstitial pneumonia (n=6), pneumonia with thoracic effusion (pleural or pericardial) (n=11), disseminated (n=10), osteomyelitis (n=3) and external abscessation (n=3) both without pulmonary disease. Statistical differences in titre distribution were found between the abortion category and the pulmonary category (P=0.003), the abortion category and pneumonia with thoracic effusion (P=0.001), the abortion category and disseminated disease (P=0.001), and the pulmonary form and pneumonia with effusion (P=0.001). The other categories had overlapping titre results. Higher serological antibody titres seemed to be associated with a poorer prognosis for survival. Categories with the highest titres, disseminated (geometric mean titre=104) and pneumonia with thoracic effusion (geometric mean titre=226), were overwhelmingly fatal (19/21 known deaths) due to severe clinical disease. The categories with lower titres, abortion (geometric mean titre=4), bone involvement only (geometric mean titre=13) and cutaneous (geometric mean titre=5), had a better survival rate (10/12 known survivors) and less severe clinical disease. Measurement of serological titre may be a useful diagnostic aid in establishing form and severity of disease and thus inform prognosis.