Rachel R. Richardson and Craig A. Watkins Mycobacterium avium subspecies paratuberculosis (MAP) is the causative agent of Johne’s disease (JD). This acid-fast staining mycobacterium primarily infects ruminants although it is known to reside in wildlife reservoirs, e.g. in rabbits and mice (Greig et al. 1997; Carta et al. 2013). Few cases of JD were reported in deer pre-1980s. However, with the increase in deer farming since the 1990s, the disease has been more frequently reported across several deer species in wild, captive and farmed herds, across all continents except Antarctica (O’Brien et al. 2020; Table 18.1). As a result, JD in deer has become an important welfare and production issue. Table 18.1 Deer species and location where infection with Mycobacterium avium subspecies paratuberculosis (MAP) has been reported. Although published results suggest subtle differences between the dynamics of MAP infection and disease progression between sheep and cattle, disease progression in deer is distinctly different. As with other ruminants, young deer are generally more susceptible to MAP infection. Young calves/fawns and yearlings can develop clinical disease, becoming infected and losing condition rapidly over weeks rather than months, where the rate of decline correlates with infective dose (Mackintosh et al. 2007, 2010a, 2010b, 2012). Alternatively, deer can develop clinical-stage disease at an age between 8 and 27 months following a similar trajectory to that of cattle, where, after a period of latency, clinical signs develop over months (Mackintosh et al. 2004; Bannantine and Bermudez 2013). If a period of latency is observed, infection can remain dormant for several years and clinical signs develop much later in the animal’s life (Mackintosh et al. 2010a). As in other ruminants, this subclinical period may never progress to clinical stages in deer. In the subclinical phase of infection, young deer will exhibit reduced growth rates, older deer produce fewer fawns and velvet production is reduced in stags (Palmer et al. 2019). During clinical stages, JD presents as a loss of body condition and eventual death. Clinical signs include a rough or moth-eaten appearance to their coat, bottle jaw and sporadic or continuous diarrhoea (Figure 18.1). Diarrhoea can be an indicator of clinical JD although it may not be seen consistently in deer. This sign can also be confused with other infections or coinfections, such as roundworm (O’Brien et al. 2020; Mackintosh et al. 2012). Figure 18.1 The life cycle of infection and transmission of Johne’s disease in deer. Johne’s Disease develops into granulomatous lesions in the small intestine and tuberculosis (TB)-like lesions in the associated lymph nodes, leading to malabsorption of nutrients in the gut, resulting in weight loss (Hunnam et al. 2013; Mackintosh et al. 2008). Disease progression has been described as a two-stage process whereby a mild, paucibacillary stage leads to a more severe multibacillary stage. Defining these stages of disease can be challenging as not all characteristics of a stage can be identified consistently. In the paucibacillary stage, the histopathology may be less pronounced with fewer granulomatous lesions and Ziehl–Neelsen (ZN) positive mycobacteria, with a trend towards smaller macrophages and increased numbers of Langhan’s giant cells (Sheehan and Hrapchak 1980). In the multibacillary stage, the mucosa of the terminal ileum takes on a corrugated appearance (Figure 18.2). This reflects the erosion of the mucosa and villi in the terminal ileum and adjacent valve. These areas of infection, as well as lesions in the ileum and jejunum, may also show large numbers of infiltrating immune cells including eosinophils, macrophages and Langhan’s giant cells, where the latter two cell types contain large numbers of ZN acid-fast mycobacteria (Figure 18.3; Power et al. 1993; Clark et al. 2010; Wherry et al. 2023). Other gross pathological evidence can be oedema in the body cavity and adhesions of the omentum to affected lymph nodes. Mesenteric and occasionally retropharyngeal lymph nodes may also have bovine TB-like caseous lesions (Nyange et al. 1992; Gilmour and Nyange 1989; Mackintosh et al. 2004). Figure 18.2 Postmortem image showing the corrugated appearance of the mucosa of the terminal ileum in a sheep with Johne’s disease. Moredun Research Institute. Figure 18.3 Histological findings in the gut of sheep with Johne’s disease (infection with Mycobacterium avium subspecies paratuberculosis (MAP)). (a) The histopathology following haematoxylin and eosin (H&E) staining of the terminal ileum from (i) asymptomatic, (ii) paucibacillary and (iii) multibacillary sheep as representative images of the histopathological progression of Johne’s disease. (i) Inset shows normal tissue histology of an asymptomatic case, normal villous architecture and inflammatory component of lamina propria within normal limits. (ii) Inset shows mixed inflammatory infiltrate into lamina propria comprising lymphocytes, eosinophils, macrophages and multinucleate giant cells. (iii) Inset shows infiltration of the lamina propria by sheets of epithelioid macrophages distending the propria and flattening the surface mucosa resulting in malformation of villi. Images are acquired at ×250 and inset at ×400 magnification. (b) The MAP (purple) bacterial load following Ziehl–Nielsen staining of the terminal ileum from (i) paucibacillary, where mycobacteria are absent and (ii) multibacillary sheep where many intracellular mycobacteria associated with the infiltrating macrophages can be observed. Source: With permisssion from Smeed et al. (2007)/Springer Nature/CC BY 2.0. The immune responses to MAP vary with disease progression, with severely diseased deer showing raised proinflammatory cytokine responses when compared to earlier stages of infection. This immune response is believed to result in the pathology seen during clinical JD (Mackintosh et al. 2011). A number of laboratory diagnostic assays have been developed to test individual deer for MAP infection including ZN-stained faecal smears, faecal and tissue culture, serology, postmortem examination, immunological assays and histology. DNA polymerase chain reaction (PCR) and quantitative polymerase chain reaction (qPCR) can be done from blood, faeces or tissue samples. Unfortunately, no one test is able to detect all stages of MAP and the sensitivity and specificity varies between diagnostic approaches. As a result, the selection of a diagnostic test and its interpretation should be carefully considered. The use of gross and histopathology as a diagnostic tool can be a useful. The development of several scoring systems has helped to provide consistency between the diagnosis and severity of the disease (Mackintosh et al. 2007; Clark et al. 2010, 2011). However, even when using such scoring systems, Johne’s disease may be mistaken for the similar effects caused by Mycobacterium bovis and Mycobacterium avium subspecies avium, being present as an infection or coinfection instead of MAP (de Lisle et al. 1993). In such cases, the diagnosis should be complemented with an alternative diagnostic test such as qPCR, to confirm the presence of MAP. Culture from postmortem tissue or faecal samples from live deer is traditionally viewed as the ‘gold standard’ test for viable MAP. Several systems have been developed to improve the sensitivity and consistency of culture including the ESP para-JEM liquid culture system (TREK Diagnostic Systems, Cleveland, OH, USA; Forde et al. 2012) and the BACTEC system (Whittington et al. 1999). However, the use of culture is less popular due to the slow growth of MAP (12–16 weeks in culture; Whittington 2020) and has therefore largely been replaced by molecular methods. Faecal PCR or qPCR have become the diagnostic test of choice for antemortem detection and quantification of MAP bacterial load, with tests commercially available (Dzieciol et al. 2010; Prendergast et al. 2018; Leite et al. 2013; Russo et al. 2022). Although the most popular sequences used are from the insertion sequence (IS) 900, other regions of the MAP genome have also been successfully used and commercialised (for example ISMav2, f57 and ISMAP02 sequences; Stabel and Bannantine 2005; Strommenger et al. 2001; Vansnick et al. 2004). Detection of a single gene (for example the f57 gene) is more accurate in counting the number of MAP genomes than the IS regions. This is because a variable number of these IS genes can be found in different strains of MAP. For example, there are between 16 and 22 copies of IS900 within the MAP genome, making quantification of bacteria difficult (Conde et al. 2021). In addition to faecal PCR, these molecular tests have been optimised to detect MAP from different types of samples including blood, milk, tissue and environmental (for example from soil and water). However, the reliability of these tests is dependent on the extraction of high-quality DNA (Park et al. 2014). A caveat of PCR is that the detection of MAP DNA does not conclusively prove that the DNA was from a viable MAP organism. This would have to be validated by growing samples in culture. There has been progress in developing tests that would also include molecular markers for viability, although these are not yet commercially available (Ricchi et al. 2014; Cechova et al. 2021, 2022). Antibody levels are detectable in deer in response to MAP infection (Griffin et al. 2005). When present, this response has been utilized for the development of blood antibody tests such as the IDEXX and Paralisa™ diagnostics kits. The former depends on cross-reactivity of the specific antibodies between species of deer and therefore requires quality control checks for each deer species tested (Pruvot et al. 2013). The Paralisa™ kit is an IgG1 antibody enzyme-linked immunosorbent assay (ELISA) based on two antigens, a MAP protoplasmic antigen and a purified protein derivative Johnin. These two antigens are read in parallel, with a positive result from either being conclusive for MAP infection. The specificity and sensitivity of the Paralisa™ test is high in late-stage clinical disease, but sensitivity reduces significantly at early stages of infection (Griffin et al. 2005; Stringer et al. 2013a). New antibody-based ELISAs are continuing to be designed and evaluated (Hermida et al. 2020). Currently, there are no cytokine-based diagnostic assays commercially available with the withdrawal of Cervigam®. This test was developed specifically to detect interferon-gamma (IFN-γ), which is considered an immuno-biomarker for early detection of MAP infection (Robinson et al. 2008; Palmer et al. 2007). The commercially available Actiphage® Rapid assay (PBD Biotech Ltd., UK) detects viable MAP in the blood of deer (Kubala et al. 2021). The test uses mycobacteriophage D29 as a lysing agent to burst low numbers of viable mycobacteria cells, releasing the genomic DNA that is then detected by qPCR assays. However, due to the difficulties associated with working with phage and its specificity, the use of this assay format is not used widely (Grant 2021; Swift et al. 2013, 2020). Routes of infection are determined by several factors and have implications for the control of disease. Vertical transmission, where MAP is passed from hind to calf/doe to fawn during the period immediately before or after birth, can occur. Intra-uterine transmission appears to be significantly more prevalent in deer than in other ruminants, with an observed transmission rate of 78–90% in foetuses during pregnancy in infected does (Thompson et al. 2007; van Kooten et al. 2006). This compares with lower rates in infected cows (39%) and sheep (<10%) (Whittington and Windsor 2009; Mackintosh and Griffin 2010b). Milk and colostrum may also act as vectors for vertical transmission, similar to that seen in sheep and cattle (Thompson et al. 2007). Horizontal transmission, where MAP is transmitted among individuals of the same generation, occurs via two main routes, either due to farm management methods or faecal–oral contamination, due to faecal shedding of MAP. This increases as the disease progresses from paucibacillary to multibacillary (O’Brien et al. 2013). Farming methods using mixed species and all-year grazing can be a major factor in horizontal MAP transmission due to environmental MAP within contaminated soil and slurry on pasture, and in water. Ruminants, as well as wildlife, all potentially contribute to this contamination, resulting in cross-species infection (Fritsch et al. 2012). Faecal–oral transmission is thought to be the main route of MAP infection from contaminated teats, soil, bedding and water (Rhodes et al. 2013; Fawcett et al. 1995).
Chapter 18
Gastrointestinal Diseases in Deer – Mycobacterium avium subspecies paratuberculosis and Johne’s Disease
Background
Deer species
Location
Reference
Herd type
Fallow deer (Dama dama)
Spain, Scotland and Tasmania
Riemann et al. (1979); Temple et al. (1979); Marco et al. (2002); Reyes-García et al. (2008); de Lisle et al. (1993); Simpson et al. (2012); Jackson et al. (2021)
Free living: wild, zoo or game park
Sika deer (Cervus nippon)
Scotland
Temple et al. (1979); de Lisle et al. (1993); Simpson et al. (2012)
Free living: wild, zoo or game park
White-tailed deer (Odocoileus virginianus)
Connecticut, USA; Saskatchewan, Canada
Chiodini and Van Kruiningen (1983); Woodbury et al. (2008); Palmer et al. (2019)
Free living: wild, zoo or game park
Axis deer (Axis axis)
California, USA
Riemann et al. (1979)
Free living: wild, zoo or game park
Red deer (Cervus elaphus)
Scotland, Spain, Czech Republic, Italy, Austria and Norway
Vance (1961); Marco et al. (2002); Reyes-Garcia et al. (2008); Pavlik et al. (2000); Machackova et al. (2004); Kopecna et al. (2008); Robino et al. (2008); Galiero et al. (2018); Nebbia et al. (2000); Glawischnig et al. (2006); de Lisle et al. (1993); Simpson et al. (2012); Tryland et al. (2004)
Farmed
Tule elk (Cervus canadensis nannodes)
California, USA
Jessup et al. (1981)
Free living: wild, zoo or game park
Reindeer/caribou (Rangifer tarandus)
Canada, Greenland and Norway
Forde et al. (2012); Tryland et al. (2004)
Semi-domesticated or wild
Roe deer (Capreolus capreolus)
Czech Republic, Italy, Scotland and Norway
Hillermark (1966); Pavlik et al. (2000); Machackova et al. (2004); Kopecna et al. (2008); Robino et al. (2008); Galiero et al. (2018); de Lisle et al. (1993); Simpson et al. (2012); Tryland et al. (2004)
Wild, free living, farmed
Moose (Alces alces)
Norway
Tryland et al. (2004)
Free living
Reeves’ muntjac (Muntiacus reevesi)
UK
Pearce et al. (2023)
Wild
Disease Progression and Clinical Signs
Gross Pathology, Histopathology and Immunology
Diagnosis
Gross and Histopathology
Culture
Polymerase Chain Reaction
Enzyme-linked Immunosorbent Assay
Phage-based Assays
Transmission
Vertical
Horizontal
Prevalence, Surveillance and Epidemiology
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
