Pyogranulomatous Pneumonia Research Articles

Protective immune response against Rhodococcus equi: An innate immunity-focused review.

Rhodococcus equi causes pyogranulomatous pneumonia in foals and immunocompromised people. Despite decades of research efforts, no vaccine is available against this common cause of disease and death in foals. The purpose of this narrative review is to summarise the current understanding of interactions between R. equi and the host innate immune system, to describe features of the immune response that are associated with resistance or susceptibility to R. equi infection, and help guide strategies for developing novel approaches for preventing R. equi infections. Virulence of R. equi in foals has been attributed to the virulence associated protein A which allows intracellular survival in macrophages by preventing acidification of R. equi-containing vacuole. Additionally, foal susceptibility to R. equi infection is associated with immaturity and naivety of innate and adaptive immune systems, while adult horses with fully functional immune system are resistant to pneumonia. Specific interaction between R. equi and innate immune cells can result in bacterial survival or death; learning how to manipulate these responses to control infection is critical to prevent pneumonia in foals. Administration of live vaccines and stimulation of innate immune responses appears to improve foals' immune response and has the potential to overcome the challenges of foal active vaccination and elicit protection against pneumonia.

First description of Rhodococcus equi infection in common bottlenose dolphin (Tursiops truncatus).

Rhodococcus equi is a terrestrial bacterium and a common pathogen in foals (Equus caballus), in which causes pneumonia. This report describes for the first time the infection caused by R. equi in a common bottlenose dolphin (Tursiops truncatus) stranded in the Calabrian coast, Italy. The post mortem examination of the animal revealed lesions in lung and colon. The animal was also positive to dolphin morbillivirus. The histological study showed lesions attributable to R. equi infection, such as pyogranulomatous bacterial pneumonia and chronic granulomatous colitis. Whole genome sequencing of the isolated strain confirmed its identification as R. equi.

Disseminated histoplasmosis in an imported Maine Coon cat in western continental Europe

AbstractA 4‐year‐old, male, neutered Maine Coon presented with a 9‐month history of weight loss, tachypnoea, dyspnoea and lethargy. The patient had been in the owner's possession since kittenhood in Texas, and 20 months before presentation had moved to Europe, living first in France and then the Netherlands. A bronchoalveolar lavage performed by the referring veterinarian cultured positive for Mycoplasma (unknown species), and treatment was initiated with minimal response. Sequential referring radiographs showed progressive diffuse pulmonary broncho‐interstitial changes. At presentation, focused echocardiogram suggested moderate likelihood of pulmonary hypertension. Repeat thoracic radiographs showed markedly progressed pulmonary changes, with a new miliary component. Bloodwork showed hypergammaglobulinaemia. Pending additional diagnostic results, the patient passed away within 4 days. Postmortem examination was compatible with severe chronic pyogranulomatous pneumonia with pleuritis, splenitis, hepatitis and adrenalitis, with histopathological identification of intracytoplasmic fungal elements. Sequencing of pulmonary granulomatous tissue confirmed the presence of Histoplasma capsulatum.

Nasal trichosporonosis in 2 mixed-breed ewes.

Two adult mixed-breed ewes were presented with a 2-wk history of upper respiratory disease. Both animals were depressed, with bilateral serosanguineous nasal discharge and harsh bronchovesicular sounds accompanied by crackles and wheezes on auscultation. One animal was recumbent and was euthanized at presentation. The other animal with similar signs, as well as exophthalmos, was euthanized because of a mass in the nasal passages. On autopsy, severe pyogranulomatous and necrotizing ethmoidal rhinitis with focal pyogranulomatous pneumonia was diagnosed in both animals. An intralesional fungal organism was identified in the nares and lungs of both animals. The organism could not be isolated via fungal culture but was identified as Trichosporon sp. by a PCR assay. Trichosporon spp. are rarely associated with disease in veterinary medicine. This ubiquitous fungus might cause disease following trauma to the nasal passages or secondary to immunocompromise.

Causes and Lesions of Fatal Pneumonia in Domestic Cats

Pneumonia in cats may cause severe lung injury and consequent death. We describe the post-mortem findings and aetiologies of naturally fatal pneumonia in 78 domestic cats, using gross and histopathological examinations, immunohistochemistry and microbiological techniques. Morphological patterns found were bronchopneumonia (27/78), interstitial (15/78), bronchointerstitial (13/78), granulomatous (8/78), aspiration (8/78) and pyogranulomatous (5/78) pneumonia, and pleuropneumonia (2/78). Bacterial pneumonia was identified as the most common cause (32/78), followed by viral (15/28 feline calicivirus, 10/28 felid alphaherpesvirus 1 and 3/28 both viruses), aspiration (8/78), fungal (5/78) and parasitic pneumonia (5/78). Co-infection with feline immunodeficiency virus and feline leukaemia virus was found in 54 cats. Viral infections involved cats of all ages, indicating the importance of investigating viral causes in cats with respiratory diseases, including in adult and ageing cats.

Detection of asinine gammaherpesviruses in association with pulmonary fibrosis in free-ranging donkeys.

A mortality event among recently captured feral donkeys (Equus asinus) occurred in south-central Utah in 2016. The deaths were sporadic, and clinical signs were indicative of respiratory disease, likely associated with an infectious etiology. Ten of 13 donkeys autopsied had moderate-to-severe interstitial fibrosing pneumonia, and one had pyogranulomatous pneumonia. Consensus PCRs directed toward the DNA polymerase and DNA packaging terminase subunit 1 for herpesviruses were performed followed by sequencing of the PCR amplicons and phylogenetic analysis. Asinine herpesvirus 4 (AsHV4) and 5 (AsHV5) were consistently identified in lung tissues of affected donkeys. No other herpesviruses were identified, and herpesviral DNA was not detected in lung tissues of 2 donkeys without evidence of respiratory disease. The detection of asinine gammaherpesviruses may have been associated with the lesions described. AsHV4 and AsHV5 have been reported in previous studies as novel gammaherpesviruses based on sequences obtained from donkeys with interstitial pneumonia and marked syncytial cell formation. Our findings suggest that the association of asinine gammaherpesviruses with respiratory conditions in equids deserves further attention.

Pneumonia in Cats associated with Neisseria sp.

Abstract Neisseria sp. is a Gram-negative diplococcus bacterium usually present on the mucosal surfaces of animals without causing an obvious pathology. The objective of this study was to report the isolation of Neisseria sp. from severe cases of pyogranulomatous pneumonia with the formation of a Splendore-Hoeppli structure in two cats treated at a veterinary hospital. This paper suggests that the Neisseria genus members may be involved in lower respiratory tract infections in cats, with the molecular diagnosis being a necessary method for the correct identification of this bacteria in animals.

Pulmonary Actinomycosis in South Australian Koalas (Phascolarctos cinereus).

Pneumonia has been reported in both free-ranging and captive koalas and a number of causative agents have been described. Between 2016 and 2019, 16 free-ranging and 1 captive koala (Phascolarctos cinereus) from the Mount Lofty Ranges of South Australia were identified with pyogranulomatous lobar pneumonia, which involved the left caudal lobe in 14/17 (82%) cases. Within lesions, numerous gram-positive or gram-variable, non-acid-fast filamentous bacteria were observed in association with Splendore-Hoeppli phenomenon. Culture yielded growth of anaerobic bacteria, which were unidentifiable by MALDI-TOF-MS (matrix-assisted laser desorption ionization-time of flight mass spectrometry) analysis in 5/5 cases. Sequencing of the bacterial 16S rRNA gene identified a novel Actinomyces species in 4 samples, confirming a diagnosis of pulmonary actinomycosis. Concurrent examination of resin lung casts from healthy koalas suggested greater laminar flow of air to the left caudal lung lobe in koalas. Actinomyces spp. have been reported as commensals of the oral microbiome in other species, and an association with similar pulmonary lesions in other species. Considering the predilection for involvement of the left caudal lung lobe, aspiration is suggested as the likely cause in some cases of pulmonary actinomycosis in koalas. Pulmonary actinomycosis has not been previously described in koalas and further work needs to be undertaken in order to classify this organism within the Actinomyces genus.

Identification of genes required for the fitness of Rhodococcus equi during the infection of mice via signature-tagged transposon mutagenesis.

Rhodococcus equi is a Gram-positive facultative intracellular bacterium that causes pyogranulomatous pneumonia in foals and immunocompromised people. In the present study, signature-tagged transposon mutagenesis was applied for the negative selection of R. equi mutants that cannot survive in vivo. Twenty-five distinguishable plasmid-transposon (plasposon) vectors by polymerase chain reaction (PCR), each containing a unique oligonucleotide tag, were constructed and used to select the transposon mutants that have in vivo fitness defects using a mouse systemic infection model. Of the 4,560 transposon mutants, 102 mutants were isolated via a real-time PCR-based screening as the mutants were unable to survive in the mouse model. Finally, 50 single transposon insertion sites were determined via the self-cloning strategy. The insertion of the transposon was seen on the virulence plasmid in 15 of the 50 mutants, whereas the remaining 35 mutants had the insertion of transposon on the chromosome. The chromosomal mutants contained transposon insertions in genes involved in cellular metabolism, DNA repair and recombination, gene regulation, non-ribosomal peptide synthesis, and unknown functions. Additionally, seven of the chromosomal mutants showed a reduced ability to multiply in the macrophages in vitro. In this study, we have identified several biosynthetic pathways as fitness factors associated with the growth within macrophages and survival in mice.

Causes and Pathology of Equine Pneumonia and Pleuritis in Southern Brazil

We document the causes and pathological findings in 50 cases of equine pneumonia and pleuritis in Southern Brazil. Suppurative (17/50), pyogranulomatous (14/50), aspiration (5/50), mycotic (4/50), bronchointerstitial (3/50), embolic (3/50) and eosinophilic granulomatous pneumonia (1/50) and pleuritis (3/50) were the main conditions identified. Streptococcus spp. were identified in 11 cases of suppurative pneumonia. Suppurative pneumonia was further divided into acute (8/17), subacute (6/17) and chronic (3/17) based on the morphological pattern of lesions. Rhodococcus equi was identified in all cases of pyogranulomatous pneumonia and exclusively affected young foals.

Assessment of Antimicrobial Susceptibility of Virulent Strains of Rhodococcus equi Isolated From Foals and Soil of Horse Breeding Farms With and Without Endemic Infections

Rhodococcus equi is an opportunistic, intracellular saprophyte that causes severe pyogranulomatous pneumonia in foals. The bacterium displays in vitro susceptibility to many antibiotics. The highest efficacy against R. equi in vitro and in vivo is achieved by using a combination of rifampicin and macrolide antibiotics. Recent years have seen an upward trend in the minimum inhibitory concentration (MIC) of rifampicin and erythromycin, suggesting increasing resistance of R. equi to these antibiotics. The aim of the study was to determine the antimicrobial activity of 24 selected antibiotics against R. equi strains isolated from dead foals and from the environment of horse breeding farms with and without endemic R. equi infections. Minimum inhibitory concentration gradient strips were used to determine the lowest concentration of the antibiotic that inhibited the growth of R. equi. Based on normal MIC distribution, an epidemiologic cutoff values (ECOFF) were assessed for particular antibiotics and R. equi strains. The results were compared with ECOFFs for S. aureus, according to the European Committee on Antimicrobial Susceptibility Testing data. The data indicate that the lowest MIC values were obtained for clarithromycin, rifampicin, imipenem, and vancomycin. The majority of R. equi strains can be classified as wild type in relation to the majority of antibiotics. A small percentage of strains presented non-WT (NWT) with the exception of SXT, for which 35% of strains were classified as NWT. The lack of interpretative criteria for R. equi creates a real problem in the assessment of antibiotic sensitivity both for clinical and scientific purposes.

Clinical and pathological findings of Rhodococcus equi infection in foals

ABSTRACT: Infection by Rhodococcus equi is considered one of the major health concerns for foals worldwide. In order to better understand the disease’s clinical and pathological features, we studied twenty cases of natural infection by R. equi in foals. These cases are characterized according to their clinical and pathological findings and immunohistochemical aspects. Necropsy, histologic examination, bacterial culture, R. equi and Pneumocystis spp. immunohistochemistry were performed. The foals had a mean age of 60 days and presented respiratory signs (11/20), hyperthermia (10/20), articular swelling (6/20), prostration (4/20), locomotor impairment (3/20) and diarrhea (3/20), among others. The main lesions were of pyogranulomatous pneumonia, seen in 19 foals, accompanied or not by pyogranulomatous lymphadenitis (10/20) and pyogranulomatous and ulcerative enterocolitis (5/20). Pyogranulomatous osteomyelitis was seen in 3 foals, one of which did not have pulmonary involvement. There was lymphoplasmacytic (4/20), lymphoplasmacytic and neutrophilic (1/20) or pyogranulomatous arthritis (1/20), affecting multiple or singular joints. Immunohistochemistry revealed to be a valuable tool for the detection of R. equi, confirming the diagnosis in all cases. Furthermore, pulmonary immunostaining for Pneumocystis spp. demonstrates that a coinfection with R. equi and this fungal agent is a common event in foals, seen in 13 cases.

Hemorrhagic pneumonia in neonatal minks in Greece concomitant with Leismania infantum detection.

In the present study a severe outbreak of hemorrhagic pneumonia (HP) in neonatal minks concomitant with Leismania infantum (L. infantum) detection is reported. The outbreak took place on a Greek mink farm and affected 1,362 mink kits, with 524 dying. Macroscopic lesions of 14 necropsied affected kits were confined to the respiratory system with dark red, consolidated lung lobes and to the small intestine with severe, acute, hemorrhagic and necrotic enteritis. Microscopic examination of lung sections revealed severe hemorrhagic pyogranulomatous pneumonia. Bacteria were obtained in pure culture from the lungs of all necropsied animals and were confirmed as Pseudomonas aeruginosa (P. aeruginosa). Three out of 14 (21.4%) animals were positive for the presence of L. infantum DNA. The outbreak was attributed to the infection of minks with P. aeruginosa, possibly as a consequence of being immuno-suppressed by L. infantum. Further research is necessary, especially on the pathogenesis of P. aeruginosa/L. infantum co-infection and the implications of this interaction on HP disease outcome.

Development of septic polysynovitis and uveitis in foals experimentally infected with Rhodococcus equi.

Rhodococcus equi is one of the most important causes of disease in foals. Infection is typically characterized by pyogranulomatous pneumonia although extrapulmonary infections occur occasionally. Uveitis and polysynovitis have been reported in foals naturally infected with R. equi and are thought to be the result of an immune-mediated process. However, the pathogenesis of these conditions is poorly understood. The objectives of this study were to document the occurrence of uveitis and polysynovitis after experimental infection with R. equi and to determine if these disorders are the direct result of infection at these sites. Foals between 3 and 4 weeks of age were infected intratracheally with virulent R. equi using inocula of 1×108 CFU (high inoculum; n = 16) or 1×107 CFU (low inoculum; n = 12). Foals were monitored twice daily and necropsy was performed 14 days post-infection. Aqueous humor and synovial fluid were collected aseptically and the percentage of affected lung was calculated. The mean (± SD) percentage of affected lung was significantly higher with the high inoculum (31.8 ± 14.6%) than with the low inoculum (14.4 ± 11.4%). Fourteen of 25 foals developed uveitis and 20 of 28 foals developed polysynovitis. R. equi was cultured from the aqueous humor of 11 foals and from the synovial fluid of 14 foals. The risk of development of polysynovitis and protein concentration in the aqueous humor were significantly higher in foals that received the high inoculum. These results indicate that polysynovitis and uveitis are septic complications associated with the severity of lung disease.

Systemic Loss of C-terminal Src Kinase Expression Elicits Spontaneous Suppurative Inflammation in Conditional Knockout Mice.

C-terminal Src kinase (Csk) is one of the critical negative regulators of the Src family of kinases. The Src family of kinases are nonreceptor tyrosine kinases that regulate inflammation, cell proliferation, motility, and adhesion. To investigate potential histologic lesions associated with systemic loss of Csk gene activity in adult mice, conditional Csk-knockout mice were examined. Cre-mediated systemic excision of Csk induced by tamoxifen treatment resulted in multiorgan inflammation. Specifically, induction of Csk gene excision with three days of tamoxifen treatment resulted in greater than 90% gene excision. Strikingly, these mice developed enteritis that ranged from minimal and suppurative to severe, fibrinonecrosuppurative and hemorrhagic. Other inflammatory lesions included suppurative pneumonia, gastritis, and myocarditis, and increased numbers of inflammatory cells within the hepatic parenchyma. When tamoxifen treatment was reduced from three days to one day in an effort to lower the level of Csk gene excision and limit lesion development, the mice developed severe suppurative to pyogranulomatous pneumonia and minimal to mild suppurative enteritis. Lesions observed secondary to Csk gene excision suggest important roles for Csk in downregulating the proinflammatory activity of the Src family of kinases and limiting neutrophil-mediated inflammation.

The pathogenesis of paraesophageal empyema in dogs and constancy of radiographic and computed tomography signs are linked to involvement of the mediastinal serous cavity.

The mediastinal serous cavity is a normal anatomic space in the caudal mediastinum. Aims of this anatomic and case series study were to describe the signs of pathologic expansion of the mediastinal serous cavity observed during computed tomography (CT), review the underlying anatomy, perform a literature review, and evaluate the medical records of several dogs with mediastinal serous cavity empyema (paraesophageal empyema). The mesothelial lined mediastinal serous cavity is a cranial extension of the omental bursa, separated from the peritoneal cavity by the diaphragm, in the dorsal part of the caudal mediastinum, to the right of the esophagus, between the heart base and diaphragm. In five adult, large-breed dogs with surgically and histologically confirmed paraesophageal empyema, macroscopic plant material was found at surgery in two dogs, adherence to adjacent lung was present in three different dogs, accessory lobectomy was performed in two dogs with subacute-chronic pyogranulomatous pneumonia, and one dog had concurrent pyothorax and mediastinitis, but none had esophageal abnormalities. This study expands our understanding of the pathogenesis and basis for the imaging appearance of paraesophageal empyema in dogs by clarifying the underlying anatomic structures that direct development of this condition. The term empyema accurately describes this condition because the purulent material accumulates within an existing body cavity. The study also provides initial evidence that the development of paraesophageal empyema might be due to local extension of lung disease, such as foreign body migration or pneumonia. Computed tomography was helpful for diagnosis, assessing size, and determining the spread of disease.

Guinea pig infection with the intracellular pathogen Rhodococcus equi

Rhodococcus equi is an opportunistic, intracellular pathogen that causes pyogranulomatous pneumonia in foals and immunocompromised people. Currently, there is no experimental model of R. equi pneumonia other than intra-bronchial experimental infection of foals with R. equi, which is labor-intensive and costly. This study’s objective was to develop a guinea pig (GP) model of R. equi pneumonia that would facilitate development of novel approaches for controlling and preventing this disease. Guinea pigs were infected with either 101, 102, 103, or 104 colony forming units (CFUs) of a virulent strain of R. equi using a Madison aerosol chamber, or 106 or 107 CFUs of this strain intratracheally. Animals were monitored daily for clinical signs of pneumonia, and were euthanized and necropsied on days 1, 3, 7, or 35 post-infection (PI). Lung homogenates were plated onto selective agar to determine bacterial load. No clinical signs of disease were observed regardless of the inoculum dose or infection method. No bacteria were recovered from GPs euthanized at 35 days PI. Histology and immunostaining of T-cells, B-cells, and macrophages in lungs showed that inflammatory responses in infected GPs were similarly unremarkable irrespective of dose or route of infection. Guinea pigs appear to be resistant to pulmonary infection with virulent R. equi even at doses that reliably produce clinical pneumonia in foals.

Vaccination of Mice with Virulence-Associated Protein G (VapG) Antigen Confers Partial Protection against Rhodococcus equi Infection through Induced Humoral Immunity.

Rhodococcus equi is a facultative intracellular bacterium causing severe pyogranulomatous pneumonia, ulcerative enterocolitis, and mesenteric lymphadenopathy in foals aged less than 6 months. Less frequently, this pathogen affects various other species, such as pigs, cattle, cats, and even humans. Although rhodococcosis is treated with a combination of antimicrobial agents, resistance is developed in some cases, and thus, antimicrobial susceptibility must be monitored and managed. Considering these limitations of the current therapy and unavailability of a vaccine to prevent the disease, research is particularly focused on the development of an effective vaccine against rhodococcosis. Most vaccines undergoing development utilize the virulence-associated protein (Vap) A antigen, which was identified previously as a key virulence factor of R. equi. Nevertheless, other proteins, such as VapG, present in most virulent R. equi strains, are also encoded by vap genes located on the R. equi bacterial virulence plasmid. In the present study, we evaluated the effect of VapG immunization on the survival of R. equi-challenged mice. We used attenuated Salmonella as a carrier for VapG (Salmonella-vapG+), a procedure previously adopted to develop a VapA-based vaccine. We observed that vaccination with Salmonella-vapG+ induced both an increased IFN-γ, IL-12, and TNF-α production, and a decreased bacterial burden in organs of the R. equi-challenged mice. Nevertheless, Salmonella-vapG+ vaccination protected only 50% of the mice challenged with a lethal dose of R. equi. Interestingly, we observed an increased frequency of B cells in the spleen of Salmonella-vapG+-vaccinated mice and showed that Salmonella-vapG+-vaccinated R. equi-challenged B-cell-knockout mice did not reduce the bacterial burden. Given these results, we discussed the potential role of the humoral immune response induced by Salmonella-vapG+ vaccination in conferring protection against R. equi infection, as well as the employment of VapG antigen for obtaining hyperimmune plasma to prevent rhodoccocosis in young foals.

Induction of Reactive Intermediates and Autophagy-Related Proteins upon Infection of Macrophages with Rhodococcus equi.

Rhodococcus equi (R. equi) is an intracellular macrophage-tropic pathogen with potential for causing fatal pyogranulomatous pneumonia in foals between 1 and 6 months of age. In this study, we sought to determine whether infection of macrophages with R. equi could lead to the induction of autophagy. Murine bone marrow derived macrophages (BMDM) were infected with R. equi for various time intervals and analyzed for upregulation of autophagy proteins and accumulation of autophagosomes relative to uninfected controls. Western blot analysis showed a progressive increase in LC3-II and Beclin1 levels in a time-dependent manner. The functional accumulation of autophagosomes detected with monodansylcadaverine further supported the enhanced induction of autophagy in BMDM infected with R. equi. In addition, infection of BMDM with R. equi induced generation of reactive oxygen species (ROS) in a time-dependent manner. These data are consistent with reports documenting the role of ROS in induction of autophagy and indicate that the infection of macrophages by R. equi elicits innate host defense mechanisms.

Spontaneous Lung Lesions in Aging Laboratory Rabbits ( Oryctolagus cuniculus).

Spontaneous age-related lesions of laboratory rabbits are not well documented in the contemporary scientific literature. A retrospective study of diagnostic necropsies of 36 rabbits >2 years of age found a number of common lung lesions. Fibromuscular intimal hyperplasia affected medium and to a lesser extent large pulmonary arteries and was present to a variable extent in all 36 rabbits >2 years of age. The lesions were characterized by fragmentation and/or reduplication of the internal elastic lamina (IEL), proliferation of smoothelin+/alpha-smooth muscle actin (α-SMA)+/vimentin- smooth muscle cells and fewer smoothelin-/α-SMA+/vimentin+ myofibroblasts, and intimal deposition of collagen without thrombosis, embolism, or evidence of pulmonary hypertension. Pulmonary emphysema, present in 30/36 rabbits, was characterized by the loss of alveolar septa; most affected rabbits did not have clinical signs of respiratory disease. In 8/13 rabbits of the inbred EIII/JC audiogenic strain, we identified a unique syndrome of granulomatous pneumonia containing hyaline brown to gray, globular to ring-like acellular material that was Alcian blue and periodic acid-Schiff positive. The material was immunoreactive for surfactant protein-A and had the ultrastructural appearance of multilamellar vesicles, suggesting a genetic defect in surfactant metabolism. Additionally, we found small benign primary lung tumors (fibropapillomas, 5 rabbits) not previously described. Other findings included heterotopic bone (5 rabbits), subacute to chronic suppurative bronchopneumonia, pyogranulomatous pneumonia with plant material, and pulmonary artifacts from barbiturate euthanasia solution.