The aim of this article is to describe a case of suppurative arthritis in a four-week-old lamb and provide a brief literature review of the causative agent, Helcococcus ovis (H. ovis). H. ovis is considered an emerging pathogen of humans and animals and to the author's knowledge has not previously been associated with a case of septic arthritis in any species.
The District Veterinarian was contacted by a producer in Waldegrave, near Orange, NSW in September 2019. The producer had a small flock of 300 composite ewes. The flock was closed with no introductions in the past two years. The ewes were lambing. They were in body condition score 2.5-3 and grazing a pasture of ryegrass, clover and phalaris. The pasture had been treated with chicken manure two years previously. The ewes had been vaccinated and drenched with Cydectin® Eweguard 6-in-1 vaccine four weeks prior to lambing. There had been no significant mortality in the ewes reported during lambing to date. The owner reported that at least half of the ewes were having multiple lambs. The ewes had not been scanned and therefore not fed according to the number of foetuses they were carrying. The pasture was considered sufficient quality and quantity for these ewes.
The producer had seen approximately five lambs that had developed lameness approximately 3-4 weeks after birth. They progressed to lateral recumbency and the owner could not straighten their legs. These lambs had appeared normal at birth and stood and suckled as expected. All of the affected lambs had died soon after he noticed the symptoms.
The producer found another lamb exhibiting the same signs and, after discussion with his private veterinarian, contacted the District Veterinarian to attend. The ewe lamb was approximately four weeks old and in good condition. There was no swelling of the umbilicus. She was pyrexic (temp 40.5°C). She was unable to stand and there was heat, pain and swelling of both carpi and hocks. The owner reported that she was taking a bottle well. A joint was prepared by clipping and cleaning with chlorhexidine scrub and alcohol. A sample was taken from the joint. It was thick and creamy in colour. The owner was told that the prognosis was poor due to the finding of suppurative arthritis and, even if the lamb survived the acute illness, there would be significant joint damage and persistent lameness. However, the owner wished to pursue treatment.
The producer treated the 8kg lamb with 1ml Depocillin (Procaine Penicillin 300mg/ml) intramuscularly once daily for 5 days. Metacam was prescribed in consultation with the private veterinarian (Meloxicam 20mg/ml) as an analgesic, however this medication was not used by the producer. The lamb died after three days. According to the producer, it continued to suckle well and appeared bright but could not stand and died suddenly one night after taking a bottle.
The sample obtained from the joint was placed in AMIES media and sent to EMAI for anaerobic culture and sensitivity.
A heavy pure growth of Helcococcus ovis was grown from the joint sample. A specific culture for Erysipelothrix rhusiopathiae was negative.
The pattern of profuse pure growth of H. ovis from the joint in association with the clinical signs increases the likelihood of this bacteria being the causative agent of the suppurative arthritis.
Sensitivity testing of this isolate proved difficult. The laboratory took a number of attempts to identify the appropriate test conditions for this bacterium. Penicillin was the only antibiotic suitable for testing against this organism. This isolate was found to be resistant to penicillin.
H. ovis is an uncommonly isolated bacterium. It is considered an emerging pathogen.
H. ovis is a catalase-negative, facultatively anaerobic, gram-positive cocci. The organism only grows close to the haemolysis zone of Staphylococcus aureus colonies on blood agar. After sub-culturing, it produces pinpoint, non-haemolytic, non-pigmented colonies without S. aureus (Mao et al., 2018). Biochemical methods are not reliable for H. ovis identification, however it is expected that the development of new genomic tools will assist in more expedient and accurate identification of H. ovis.
The genus Helcococcus was first characterised in 1993 (Collins et al., 1993) and identified as a new species by Collins and colleagues in 1999. Initially, two undescribed bacterial isolates were recovered from mixed cultures from geographically separate sheep. One culture was recovered from a post-mortem exam of a sheep in Scotland. A heavy growth of H. ovis and Arcanobacterium pyogenes (now named Trueperella pyogenes) was grown from the lung, liver and spleen. The other H. ovis culture was grown from the milk of a sheep in Spain with subclinical mastitis. This isolate was cultured with a Staphylococcus species. Initially it could not be cultured independently from the Staphylococcus species. In 1999, further phenotypic and molecular taxonomic methods were used to classify this unknown coccus as a new species, which was called Helcococcus ovis. The clinical significance of the organism at this time was unknown (Collins et al., 1999).
In 2003, H. ovis was isolated from a pulmonary abscess in a Quarter horse gelding in Washington, USA (Rothschild et al., 2003). In North Carolina, USA in the same year H. ovis was isolated from a vegetative heart valve lesion in a 12-month-old steer (Post et al., 2003).
The latter finding prompted research in Brandenburg, Germany in 2008. Fifty-five cases of bovine valvular endocarditis were examined and H. ovis represented the second most common isolate recovered (18 cases or 33%) (Kutzer et al., 2008).
In 2009, an outbreak of acute respiratory disease in a flock of 70 lambs was investigated in Ohio, USA. There was a morbidity of seven percent and three animals died. Pleuritis and bronchopneumonia were found on post-mortem. H. ovis was isolated in a heavy and dominant growth from the lesions. This case was the first time clinical disease was ascribed to H.ovis in sheep (Zhang et al., 2009).
In 2012, García and colleagues reported H. ovis cultured from the lungs of a goat with pulmonary abscesses and purulent bronchopneumonia as the aetiological agent. In the same year, Schwaiger detected H. ovis in four cases of bovine mastitis and proposed that it may play a role in the development of bovine mastitis. H. ovis was cultured from dairy cows with uterine infections in 2013 and the next year it was isolated as a pure growth from the stomach contents of an aborted bovine foetus.
In 2014, a study of lameness and hoof abnormalities in wild Roosevelt Elk reported H. ovis was isolated from the hooves of two of four of animals in the study, although this infection was not deemed the cause of the lameness and pedal osteomyelitis (Han & Mansfield, 2014).
In 2018, the first known human case of H. ovis was reported in association with an infection of an artificial eye. There was no known animal contact, however the person worked with wool and cowhides three months prior to the onset of symptoms (Mao et al., 2018).
The prevalence of this organism in the livestock population is unknown. The organism is likely to be under-reported because it is slow growing and requires carbon dioxide and Staphylococcus species for initial isolation. In addition, it may be associated with mixed infections and can be easily missed because of the overgrowth of other fast-growing organisms (Mao et al., 2018).
Limited information is available on antimicrobial susceptibility and resistance of H. ovis. In Germany, Sabine et al. investigated resistance patterns in bovine isolates of H. ovis. Twenty-seven isolates were examined. Erythromycin MICs of >8 mg/ml were found in three (10%) isolates and tetracycline MICs were found to be increased (>8mg/ml) for 24 (83%) isolates, indicating H. ovis resistance to these antimicrobials is frequent. Penicillin, ampicillin, amoxicillin-clavulanic acid, and cephalothin MICs were not elevated indicating no resistance to these antimicrobials detected in this study (Bilk et al., 2011). Another paper reported antimicrobial sensitivities of five Helcococcus spp. isolates tested, one being H. ovis associated with a human case of urosepsis. All these isolates had high MICs for trimethoprim-sulfamethoxazole, erythromycin, azithromycin, and clindamycin. Intermediate to high MICs for moxifloxacin, levofloxacin and gentamicin were also observed among the Helcococcus spp. (Chow & Clarridge, 2016).
Antimicrobial sensitivity testing was requested for the H. ovis isolate from the lamb's joint. This isolate was resistant to penicillin, which was the only available antibiotic suitable for testing against this organism according to current testing guidelines at the laboratory. Fortunately, no further cases of suppurative arthritis were reported by this producer.
H. ovis isolates have been recovered from sheep, cattle, horses and goats causing infections such as valvular endocarditis, pulmonary abscess, pleuritis, bronchopneumonia, mastitis, abortion and now septic arthritis. The organism should be considered as a differential diagnosis in such cases of disease in these species.