An update on joint ill in sheep

AT this time of year, sheep farmers and vets are turning their attention to the 2021 lambing season. In addition to routine annual preparations, a review of any flock problems encountered during the 2020 season is advisable. This can be used to guide a more farm-specific approach to preparing for lambing and helps formulate disease prevention protocols. For example, the links between suboptimal colostrum intake and watery mouth disease have been well documented by the Responsible Use of Medicines in Agriculture (RUMA) Alliance.¹

Infectious arthritis (or joint ill) in lambs has generally been considered to be associated with poor lambing hygiene. However, cases investigated in recent years by postmortem examination providers and universities suggest multiple risk factors for this disease. This article describes some of the suggested risk factors for joint ill to consider when preparing for the upcoming lambing season.

VIDA diagnoses

Since 2002, there have been 1085 diagnoses of arthritis in sheep recorded in the Veterinary Investigation Diagnosis Analysis (VIDA) database. The most common presenting sign recorded is lameness and musculoskeletal, but there were other clinical signs recorded in 44 per cent of the submissions (Fig A).

Details are in the caption following the image — **Fig A**
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Presenting signs recorded in sheep with a VIDA diagnosis for arthritis 2002–2020

Arthritis in sheep is classified into three VIDA diagnosis categories:

arthritis due to Streptococcus dysgalactiae;
arthritis due to erysipelas;
arthritis due to other causes.

Arthritis due to S dysgalactiae is by far the most common type of joint ill, accounting for 63 per cent of arthritis diagnoses between 2002 and 2020 (Table 1).

Table 1. Diagnoses of arthritis by cause recorded in the VIDA database, 2002–2020

Cause	Number of diagnoses
Arthritis – Streptococcus dysgalactiae	673
Arthritis – other cause	284
Arthritis – erysipelas	128

Arthritis due to S dysgalactiae

Lambs in the neonatal and preweaned age categories constituted 90 per cent of S dysgalactiae arthritis cases, where the age was recorded. In keeping with this finding, 91 per cent of the cases were recorded between February and May (Fig B).

In a study run by Scotland's Rural College (SRUC) in 2017, 59 lambs with joint ill were examined from 32 flocks.² Of those examined, 64 per cent were male, 66 per cent were between one and two weeks old and the remainder were less than four weeks old. S dysgalactiae was isolated from 18 flocks, making it the most common pathogen isolated. Indoor and outdoor lambing flocks were affected and in most cases the problem began in the first week of lambing.

Three outbreaks of S dysgalactiae joint ill investigated in England and Wales during 2020 are described below. These demonstrate the multifactorial nature of this disease with different histories and risk factors, and the possible concurrent gross pathologies encountered.

Case 1

Four two- to four-week-old lambs were submitted to investigate lameness, hindlimb gait deficits and malaise. Gross findings included polyarthritis, with excess turbid joint fluid and fibrinous material in the affected joints (Fig C). Two lambs had fibrinous material adjacent to the atlanto-occipital joint (Fig D) and one had a myocardial abscess.

S dysgalactiae was isolated from the joints of all four lambs and liver biochemistry testing revealed hypocuprosis in two lambs.

The affected lambs were single male lambs from one group. The history and investigation findings suggested that using tail and castration rings, and hypocuprosis, were all risk factors in this case.

Case 2

One 11-week-old lamb was submitted to investigate lameness, swelling of the neck, malaise and death. In a group of 160 lambs vaccinated nine days before submission, 15 lambs were affected.

PREVENTION

The cases discussed is this article illustrate that risk factors for joint ill are farm-specific and therefore prevention measures must also be targeted to the needs of individual farms. This highlights the importance of diagnostic laboratory and on-farm investigations to support appropriate flock health control plans.

Postmortem examination revealed a large injection-site neck abscess, polyarthritis and catastrophic haemorrhage within the pericardium.

S dysgalactiae was isolated from the neck abscess and joints. Histopathology identified the source of the haemorrhage as a perforation in the ventricular free wall from a necrotising and suppurative myocarditis (Fig E), with histopathology revealing intralesional bacteria suggestive of S dysgalactiae.

Case 3

A large flock with a high incidence of S dysgalactiae arthritis had been investigated by the farm's private vet and the APHA since 2017. The findings of the investigation from 2017-2019 were presented at the Sheep Veterinary Society meeting in autumn 2019.³

The flock had a high standard of general management and hygiene in the lambing shed. However, specific interventions were identified and adopted, which were followed by an improvement in the clinical situation. These included:

reduced ear-tagging;
increased lambing outdoors;
use of an autogenous vaccine for the last three lambing seasons;
culling of suspected carrier ewes;
introduction of composite breed ewes and rams into the flock.

A peak of joint ill cases occurred at four to seven days of age and was followed by a second peak when the lambs were over three weeks old. The second peak was concurrent with suboptimal vitamin E levels, and positive Anaplasma phagocytophilum PCR results (indicating tickborne fever) were identified in affected lambs.

A study in 2014 investigated the on-farm sources and likely transmission routes of S dysgalactiae.⁴ This study suggested that the most probable reservoir of S dysgalactiae was the vagina of the ewe, with possible contamination of the environment via birth fluids. The maximum recorded organism survival time on straw or hay was 35 days. No isolate survival in water was detected. Poor hygiene practices, such as lack of hand-washing, increased the risk.

Diagnosis and treatment

As with bacterial arthritis in other species, treatment in the early stages of disease is vital for a successful outcome. It is advisable to undertake bacteriology testing of untreated cases using either aseptically collected joint tap samples or postmortem examination charcoal joint swabs. (It is also advisable to collect a plain swab in case Mycoplasma testing is indicated.) This can be used to guide treatment of subsequent cases.

Resistance to tetracyclines is common in S dysgalactiae isolates⁵ and a small number of isolates from 2018 to 2020 have been resistant to cephalexin.

Chronic joint ill can be a welfare concern. Both the use of NSAIDs in the early stages of disease and euthanasia of poorly responsive cases should be considered.

Arthritis due to Erysipelothrix rhusiopathiae

Based on VIDA data, where the age group was recorded, arthritis due to E rhusiopathiae occurs more frequently in postweaned and older sheep (71 per cent), rather than preweaned (29 per cent) animals.

Infection with E rhusiopathiae, which is a soil organism, can follow any minor skin wound, such as those that occur at tagging or are acquired from rough grazing. It is also associated with ‘postdipping lameness’, which is caused by bacterial contamination and multiplication in dipping facilities, and with handling sheep through muddy or contaminated handling pens. Handling pens should be cleaned regularly and gross contamination of dips should be avoided.

In one submission affecting fattening lambs,⁶ the carpal joints and a stifle joint were markedly swollen and could not be fully flexed and the joint capsules were thickened and fibrotic. The articular surfaces showed evidence of cartilage erosion and pitting (Fig F). Bacterial cultures identified E rhusiopathiae from multiple joints and erysipelas serum agglutination tests gave high positive results.

As discussed above, bacteriology is advisable to guide treatment. Porcine erysipelas vaccines have been used as part of a control programme in flocks with recurrent issues. However, the use of these vaccines is not without risk, as suspected anaphylactoid reactions have been reported.⁷

Arthritis due to other causes

During the SRUC 2017 study, Escherichia coli, Trueperella pyogenes, Mannheimia haemolytica, Staphylococcus aureus and Fusobacterium necrophorum were also isolated from joint ill cases.

Joint ill due to T pyogenes is often associated with navel infection⁸ and visceral abscesses may also be present (Fig G). This type of joint ill can suggest suboptimal navel treatment, suboptimal colostrum intake and poor lambing pen hygiene.

Joint fluid or plain joint swabs from arthritis cases diagnosed in sheep over six weeks old at postmortem examination are used for Mycoplasma agalactiae testing. This forms part of the survey for contagious agalactia.

Summary

Joint ill in lambs has a multifactorial aetiology. S dysgalactiae is the commonest pathogen involved, but other pathogens, such as E rhusiopathiae, can be the causal agent. The following measures help to reduce the incidence and severity of joint ill:

maintaining strict hygiene of lambing pens, lambing equipment and hands;
dipping navels in a strong iodine solution at birth and again four hours later;
ensuring all lambs receive adequate colostrum;
maintaining strict hygiene of dipping facilities and handling pens;
taking appropriate hygiene measures when using injections;
monitoring vitamin and trace element levels;
monitoring tick burdens;
monitoring all lambs for early signs of illness and investigating the cause;
initiating prompt and appropriate treatment in the early stage of disease.

Liverpool university, the Moredun Research Institute and the Agriculture and Horticulture Development Board Beef and Lamb are undertaking a project and PhD entitled ‘Preventing lamb joint ill’. A survey for this project was recently completed by over 200 sheep farmers.

In conjunction with this, a working group to increase awareness of this disease has been established (JIGSAW: Joint Ill Group – Septic Arthritis Awareness). Liverpool university and the APHA have also stored isolates from cases with a view to undertaking whole genome sequencing on them, to further investigate their pathogenicity and antimicrobial resistance traits.

Abstract

VIDA diagnoses