Successful surgical debridement of a cerebral Streptococcus equi equi abscess by parietal bone flap craniotomy in a 2-month-old Warmblood foal

Brain abscesses and intracranial masses have been regularly described in horses. Treatment often is difficult and unrewarding and mortality rate high. This case report describes the successful treatment of a cerebral abscess in a 2-month-old female Warmblood foal with severe neurological signs of acute onset. Computed tomography (CT) revealed a 3 × 4 × 4 cm cerebral mass in the left brain hemisphere with severe cerebral oedema. Craniotomy, using a parietal bone flap technique, allowed the abscess to be sampled, drained and lavaged. Immediately, post-surgery the foal showed significant clinical improvement. Sample culture confirmed Streptococcus equi equi infection. The foal was medically treated for 6 weeks, leading to complete clinical and radiographical recovery. Intracranial surgery in equine medicine is limited. Using a parietal bone flap instead of partial craniectomy to gain access to the cerebrum is a less invasive procedure leading to a better aesthetic result and should be considered for the treatment of cerebral masses in the horse.     

Surgical management of Rhodococcus equi metaphysitis in a foal

A chronic Rhodococcus equi metaphysitis involving the distal growth plate of the left third metatarsal bone had induced a longstanding lameness in a young foal. Abnormal hematologic values included mild anemia, hyperfibrinogemia, mild leukocytosis, and neutrophilia. Radiography of the distal portion of MT3 revealed a radiolucent zone on the medial aspect of the growth plate, and small pieces of bone suggestive of sequestra. Treatment with erythromycin estolate and rifampin, aggressive surgical debridement, and cancellous bone grafting helped resolve the bone infection.     

Intracranial abscess caused by Rhodococcus equi infection in a foal

CASE DESCRIPTION: A 4-month-old Missouri Fox Trotter colt was examined for a 5-week history of head tilt after treatment for suspected pulmonary Rhodococcus equi infection. CLINICAL FINDINGS: Computed tomography revealed osteolysis of the occipital, temporal, and caudal portion of the parietal bones of the left side of the cranium. A soft tissue mass compressing the occipital region of the cerebral cortex and cerebellum was associated with the osteolytic bone. TREATMENT AND OUTCOME: A rostrotentorial-suboccipital craniectomy approach was performed to remove fragmented occipital bone, debulk the intracranial mass, and obtain tissue samples for histologic examination and bacterial culture. All neurologic deficits improved substantially within 3 days after surgery. Bacterial culture of the resected soft tissue and bone fragments yielded R equi. CLINICAL RELEVANCE: Intracranial surgery in veterinary medicine has been limited to dogs and cats; however, in select cases, extrapolation of surgical techniques used in humans and small animals can assist with intracranial procedures in horses.     

Cellulitis and subcutaneous abscesses caused by Rhodococcus equi infection in a foal

Cellulitis and subcutaneous abscess formation was diagnosed in a 3-month-old Thoroughbred filly. Clinical signs consisted of a large ulcerated plaque, with satellite pustules on the medial aspect of the right hock and subcutaneous abscesses in the right inguinal and mammary gland areas. Laboratory analysis revealed mature neutrophilia. Rhodococcus equi was isolated from the cellulitis and the subcutaneous abscess. Oral administration of erythromycin and rifampin for 35 days resulted in a clinical cure.     

Detection of Streptococcus equi subspecies equi using a triplex qPCR assay

Genome sequencing data for Streptococcus equi subspecies equi and zooepidemicus were used to develop a novel diagnostic triplex quantitative PCR (qPCR) assay targeting two genes specific to S. equi (eqbE and SEQ2190) and a unique 100 base pair control DNA sequence (SZIC) inserted into the SZO07770 pseudogene of S. zooepidemicus strain H70. This triplex strangles qPCR assay can provide results within 2 h of sample receipt, has an overall sensitivity of 93.9% and specificity of 96.6% relative to the eqbE singlex assay and detects S. equi at levels below the threshold of the culture assay, even in the presence of contaminating bacteria.     

Long-term successful outcome of a Streptococcus equi subspecies equi brain abscess

We previously described successful treatment, including surgical drainage, of a Streptococcus equi subspecies equi brain abscess that caused severe neurological deficits in a 7-year-old Quarter Horse mare. This report details the long-term successful outcome of the case, findings of a magnetic resonance imaging (MRI) study performed 14 years after surgery and necropsy findings 18 years after initial treatment. Despite persistent cerebral and midbrain lesions detected by MRI and at necropsy, the mare returned to serviceable function within a year of initial treatment and had a successful performance career for over 10 years until carpal arthritis prompted retirement. This case demonstrates that brain abscess in horses can be successfully managed by combined medical and surgical treatment.     

Vertebral osteomyelitis caused by Rhodococcus equi in a three-and-half-month-old Dutch Warmblood foal

Rhodococcus equi infection occurs worldwide and is especially a problem in foals, where it often causes colitis or pneumonia. Other organs are seldom affected, and their involvement is regarded as a complication of pneumonia and/or colitis. Vertebral osteomyelitis is one such rare complication and is probably caused by haematogenous spread from inflammatory lesions in the lungs and/or intestine. In rare cases, osteomyelitis can be caused by contamination of a wound. This case study describes a foal with vertebral osteomyelitis due to R. equi in which there were only minor inflammatory changes in a mesenteric lymph node.     

A case of transplacental transmission of Theileria equi in a foal in Trinidad

Equine piroplasmosis due to Theileria equi and Babesia caballi is endemic in Trinidad. A case of equine piroplasmosis due to T. equi was diagnosed in a thoroughbred foal at 10h post-partum. A high parasitaemia (63%) of piroplasms was observed in a Wright-Giemsa(?) stained thin blood smear from the foal. In addition, the 18S rRNA gene for Babesia/Theileria was amplified from DNA extracted from the blood of the foal and the mare. Amplified products were subjected to a reverse line blot hybridization assay (RLB), which confirmed the presence of T. equi DNA in the foal. The mare was negative by RLB but was positive for T. equi using a nested PCR and sequence analysis. In areas where equine piroplasmosis is endemic, severe jaundice in a post-partum foal may be easily misdiagnosed as neonatal isoerythrolysis. Foals with post-partum jaundice should be screened for equine piroplasmosis, which may be confirmed using molecular methods if available.     

Characterization of a Streptococcus equi ssp. equi Isolate From a Strangles Outbreak in Thailand

Strangles, which is caused by Streptococcus equi ssp. equi, is one of the major infectious respiratory diseases in horses. Knowledge of isolates from different areas of the world is important for investigating the different strains of the disease. In contrast to many other countries, currently little is known about S. equi ssp. equi isolates in Thailand. In 2014, a farm in Thailand imported 20 horses from Europe. Approximately 1 month after arrival, 50% of the horses had developed pyrexia, mucopurulent nasal discharge, and abscesses of the mandibular lymph nodes. Nasal swabs of mucopurulent discharge were sent to a diagnostic laboratory, and two isolates of S. equi ssp. equi were identified. One of the isolates was further characterized using seM gene polymerase chain reaction and sequence analysis. The seM sequence was then compared to the database of PubMLST-seM. It was found to contain SeM allele 48, an allele isolated from horses in the United Kingdom in 2006 and 2010. This result demonstrates the usefulness of SeM allele identification as a tool for investigating the source of related strains and for the epidemiologic study of strangles. To the best of the authors' knowledge, this is the first report of the identification of an SeM allele of the S. equi ssp. equi isolate in Thailand.     

Medical management of a large intra-abdominal mass caused by Rhodococcus equi in a foal

A 4-month-old Thoroughbred filly presented with pyrexia, inappetence and diarrhoea. Abdominal ultrasonography revealed a multilobulated abdominal mass that was determined to be associated with the caecum using computed tomography. Computed tomography also identified mesenteric lymphadenopathy and a pulmonary mass in the left caudal lung lobe. Percutaneous aspiration of the abdominal mass yielded pure growth of Rhodococcus equi. The filly responded in a positive fashion to the administration of clarithromycin, rifampin and gallium maltolate. Follow-up computed tomography revealed complete resolution of the abdominal mass and lymphadenopathy. Extrapulmonary disorders associated with R. equi should be considered even when thoracic ultrasonography reveals no evidence of pulmonary pathology. Although intra-abdominal abscesses have a grave prognosis, successful treatment is possible. Gallium maltolate can be safely administered to foals and may improve patient outcomes.     

The interaction of Rhodococcus equi and foal neutrophils in vitro

Polymorphonuclear neutrophil leukocytes (PMNL) from 8 healthy foals (2-14 weeks of age) and 2 foals with bacterial pneumonia were separated from whole blood using a 2 step Percoll gradient. Purified PMNL were tested for bactericidal function against Rhodococcus equi and Staphylococcus aureus in the presence of normal horse serum. The percentage uptake after a 15-min pre-incubation of PMNL and bacteria was also calculated. Ultrastructural examination of the interaction of R. equi and normal foal PMNL was performed after 15 min incubation. Results indicated that foal PMNL effectively phagocytose and destroy R. equi and S. aureus in the presence of normal horse serum. The mean percent uptake for R. equi was 99.3 +/- 0.4% and for S. aureus 99.9 +/- 0.1%. Further, 97.8 +/- 0.1% ingested R. equi and 98.4 +/- 0.1% ingested S. aureus were destroyed in the 15-min incubation period. Over the 3-h incubation, 91.9% of remaining R. equi were killed, but only 49.2 +/- 31.9% of S. aureus (P less than 0.01). Total bactericidal effect of foal PMNL, however, was 99.3 +/- 0.4% against R. equi and 99.9 +/- 0.1% against S. aureus. The percentage uptake and total bactericidal efficacy of neutrophils from sick foals was greater than 95%. Ultrastructural examination of the PMNL-R. equi interaction after 15 min incubation revealed phagocytosis of the bacteria and morphologic changes consistent with neutrophil degranulation. This study suggests that a defect in PMNL bactericidal capability is not likely to be a contributing factor in the pathogenesis of R. equi pneumonia in foals.     

Multiple extra-pulmonary disorders associated with Rhodococcus equi infection in a 2-month-old foal

A 2-month-old Thoroughbred filly was referred to Hagyard Equine Medical Institute for further evaluation of acute pyrexia and a suspected intra-abdominal abscess based on abdominal ultrasonography performed in the field. Initial examination revealed bilateral uveitis, polysynovitis, a large internal abdominal abscess and pneumonia. A transtracheal wash confirmed the presence of a multi-sensitive strain of Rhodococcus equi. Anaemia and thrombocytopenia were noted during hospitalisation. Results of a Coombs test were consistent with an immune-mediated haemolytic process. Recurrent pyrexia, abdominal discomfort and severe respiratory distress unresponsive to intensive medical support motivated euthanasia followed by necropsy after 30 days of treatment. Overall, six extra-pulmonary disorders were simultaneously diagnosed despite the lack of pulmonary pyogranulomas.     

Septic pleuritis and abdominal abscess formation caused by Rhodococcus equi in a foal

A 3-month-old female Arabian horse was evaluated because of fever, respiratory distress, lethargy, and decreased appetite of 5 days' duration. Pleural effusion was diagnosed on the basis of ultrasonographic and radiographic examinations. Cytologic examination of pleural fluid collected via thoracocentesis revealed septic inflammation; bacteriologic culture of a sample of that fluid yielded Rhodococcus equi. A large intra-abdominal mass adjacent to the body wall was identified ultrasonographically. A specimen of the mass was collected via aspiration; the specimen was identified cytologically as purulent exudate that contained large numbers of rod-shaped bacteria, which confirmed abdominal abscess formation. Bacteriologic culture of a sample of the exudate also yielded R. equi. The foal was treated with azithromycin (10 mg/kg [4.5 mg/lb], PO, q 24 h for 5 days then q 48 h) and rifampin (5 mg/kg [2.3 mg/lb], PO, q 12 h) for 8 weeks and metronidazole (15 mg/kg [6.8 mg/lb], PO, q 8 h) for 3 weeks. Clinically, the foal responded to antimicrobial treatment within 2 weeks. At 8 weeks after the initial evaluation, ultrasonographic examination of the foal revealed resolution of the pleural effusion and abdominal abscess. In foals, R. equi infection typically results in pyogranulomatous pneumonia, and pleural effusion is an uncommon clinical sign. The combination of azithromycin and rifampin appears to be an effective treatment for R. equi infection in foals.     

Real-time PCR for detection and differentiation of Streptococcus equi subsp. equi and Streptococcus equi subsp. zooepidemicus

Strangles is a contagious equine disease caused by Streptococcus equi subsp. equi. In this study, clinical strains of S. equi (n=24) and Streptococcus equi subsp. zooepidemicus (n=24) were genetically characterized by sequencing of the 16S rRNA and sodA genes in order to devise a real-time PCR system that can detect S. equi and S. zooepidemicus and distinguish between them. Sequencing demonstrated that all S. equi strains had the same 16S rRNA sequence, whereas S. zooepidemicus strains could be divided into subgroups. One of these (n=12 strains) had 16S rRNA sequences almost identical with the S. equi strains. Interestingly, four of the strains biochemically identified as S. zooepidemicus were found by sequencing of the 16S rRNA gene to have a sequence homologous with Streptococcus equi subsp. ruminatorum. However, they did not have the colony appearance or the biochemical characteristics of the type strain of S. ruminatorum. Classification of S. ruminatorum may thus not be determined solely by 16S rRNA sequencing. Sequencing of the sodA gene demonstrated that all S. equi strains had an identical sequence. For the S. zooepidemicus strains minor differences were found between the sodA sequences. The developed real-time PCR, based on the sodA and seeI genes was compared with conventional culturing on 103 cultured samples from horses with suspected strangles or other upper respiratory disease. The real-time PCR system was found to be more sensitive than conventional cultivation as two additional field isolates of S. equi and four of S. zooepidemicus were detected.     

Studies in atypical Streptococcus equi.

An atypical variety of Streptococcus equi is described. It was shown to be deficient in capsular material, to be very virulent for mice and to possess a cell-wall protein similar to the M-like protein of classical Str equi. Antiserum prepared against classical Str equi effectively opsonised the atypical strains, and induced the formation of long chains by these atypical strains. It is possible that this variant of Str equi can be used to overcome many of the current problems associated with the manufacture and use of strangles vaccines.