CASE IV: N-190/20 (JPC 4165839)
Signalment:
6 years old, female, Breed Rasa Aragonesa, Ovine (Ovis aries)
History:
Animal with history of chronic rhinitis, non-responsive to antibiotic treatment.
Physical findings revealed marked dyspnea, and weakness.
Gross Pathology:
The ventral conchae in the left nasal cavity was severely swollen, with a roughed, thickened mucosa compound of multiple, small, whitish or yellowish polypoid proliferations covered by abundant mucus. The proliferative mucosa was obliterating the meatus and protruding through the nostrils.
Laboratory Results:
Nasal swabs were obtained during the necropsy.
Pure cultures of Salmonella enterica subsp. diarizonae serovar 61:K:1, 5, 7 were obtained from the swabs.
Microscopic Description:
Nasal Mucosa: Up to 100% of the tissue is affected by a proliferative and inflammatory process. Diffusely the mucosa is thickened up to 5-20 times the normal, frequently forming multiple polypoid projections compound of abundant hyperplastic disorganized respiratory epithelium that contain abundant intracytoplasmic 1-2μm eosinophilic bacilli/cocobacilli. Between the epithelial cells are moderate amounts of neutrophils, lymphocytes, plasma cells, Mott cells, and macrophages, the same type of inflammatory cells are severely infiltrating and expanding the adjacent submucosa, admixing with moderate amount of edema, some areas of mild fibrosis and capillary congestion. Multifocally there is seromucous gland hyperplasia that contain abundant eosinophilic amorphous material, cellular debris and the same inflammatory cells, and intracytoplasmic bacteria previously described. Covering the mucosa is abundant eosinophilic amorphous material and few cell debris.
Contributor's Morphologic Diagnosis:
Nasal mucosa: Diffuse proliferative, lymphoplasmocytic and neutrophilic rhinitis with abundant intracytoplasmic bacilli, chronic, severe.
Condition: Chronic Proliferative Rhinitis.
Etiology: Salmonella enterica subsp. diarizonae serovar 61:K:1, 5, 7.
Contributor's Comment:
The bacteria Salmonella enterica subsp. diarizonae serovar 61: K:1,5,7 is host adapted in sheep, can colonize and persist in the nasal mucosa. Infected animals may occasionally develop chronic nasal inflammation, particularly after being stressed.4
Clinical signs started with unilateral or bilateral nasal discharge of thick mucus together with wheezing and snoring. These signs persist and progress for several weeks, with almost complete nasal obstruction caused by the presence of proliferating tissue, often visible at the nares.4
Gross findings include thickened mucosa with multifocal proliferations composed of multiple small white or yellow polypoid structures covered by mucus. The ventral turbinates appear to be more affected.4
Histological findings reveal a thickened nasal mucosa with multiple polypoid projections or layers of disorganized epithelial cells covered by hyperplasic respiratory epithelium. These cells have elongated eosinophilic cytoplasm or vacuoles filled with gram-negative bacilli. Nuclei are generally rounded with peripherally condensed chromatin and some nuclei showing degenerative changes. Groups of neutrophils invade basal or apical portions of the epithelium. The proliferative epithelium may be covered by eosinophilic amorphous material mixed with cell debris. The submucosa is expanded and densely infiltrated by plasma cells, macrophages, and neutrophils. Nasal glands are hyperplasic with variable degree by secretion.4
Investigation of affected flocks indicate direct animal to animal transmission and possible shedding of Salmonella by nasal discharge.6
There are many different diseases affecting the upper respiratory tract in sheep that could confuse the diagnosis, such as oestrosis, enzootic nasal adenocarcinoma, or fungal rhinitis.5
Salmonella enterica subsp. diarizonae has been implicated in infections of other organs as an opportunistic gastrointestinal pathogen in lambs and suppurative epididymitis and orchitis in rams.2,3
The presence of S. enterica subsp. diarizonae serovar 61:k:1,5,(7) in sheep could have public health significance, since human infections through the consumption of uncooked meat or contaminated animal products has been described.2 The prevalence of Salmonella was high in sheep and low in goats at slaughter. The tonsils allow a better estimation of the prevalence of Salmonella in asymptomatic sheep than fecal samples.1
Generally, human pathologies associated with these bacteria occur in individuals with underlying diseases. However, the kinetics of the infection are not completely understood. Further studies may clarify the prevalence of SED 61:k:1,5,(7) in different flocks and the persistence in the nasal mucosa of sheep.5
Contributing Institution:
Universidad de Zaragoza. Departamento de Patología Animal
Web: https://patologiaanimal.unizar.es
JPC Diagnosis:
Nasal mucosa: Rhinitis, proliferative and lymphoplasmacytic, diffuse, chronic, severe, with numerous intraepithelial and intrahistiocytic bacilli.
JPC Comment:
The contributor provides an excellent overview of ovine proliferative rhinitis, a unique condition first described in the United States by Meehen et al. in 1992 and has subsequently been described in Spain (2012) and Switzerland (2017).
Salmonella enterica is a facultative anaerobic, gram-negative, rod-shaped, flagellated bacterium divided into six subspecies composed of enterica, salamae, arizonae, diarizonae, indica, and houtenae. The most common subtype isolated from infected warm blooded animals and humans is S. enterica subsp. enterica whereas S. enterica subsp. diarizonae is most commonly isolated from reptiles. A notable exception to the latter is S. enterica subsp. diarizonae serovar 61:k:1,5,(7), which has been identified as being host-adapted for sheep (also known as "sheep associated S. diarizonae" or "SASd"). Two distinct lineages of this subtype are ST432 and ST439. The ST432 linage is most prevalent, with the majority of isolates historically being of ovine origin whereas all ST439 isolates have been obtained from human clinical samples. Thus, it has been proposed that the ST432 lineage of SASd is host adapted for sheep whereas STS439 is not. Despite these differences, both subtypes are highly similar, which is in turn facilitates scientific discovery as to which genetic variances favor ST432's host adaptation to sheep.7
Pseudogenetization is a phenomenon thought to facilitate the process of host-adaptation. This process occurs when previously functional and full-length genes are inactivated, disrupted, eroded, and eventually removed from the genome and is thought to occur when those genes no longer necessary for survival. Therefore, the number of pseudogenes possessed by an entity may correlate to its level of host adaption. Although STS432 and STS439 both possess an increased numbers of pseudogenes, ST432 has a significantly higher share. Examples of ST432 pseudogenes include acrD, a gene encoding a multidrug efflux transporter involved in aminoglycoside efflux, narX and phoX, two genes involved in substrate sensing and signaling, and cas3, a gene that when knocked-out has been found to result in decreased virulence and increased cellular survival, features that would in turn favor the survival of an intracellular organism.7
ST432 also possess additional unique virulence factors absent in ST432, such as five genes considered to encode fimbria with a high similarity to the P/Pap pilus gene cluster of uropathogenic E. coli, which mediate attachment to uroepithelial cells. These fimbriae are thought to facilitate intestinal colonization in sheep. An additional unique virulence factor of ST432 compared to ST439 is asr, which encodes an acid shock protein, which may facilitate intrahistiocytic survival.7
Chronic proliferative rhinitis due to SASd is rarely reported. However, SASd infection is quite common in sheep, though with variable geographical prevalence. For example, the pathogen is considered endemic in Sweden where 72% of tested farms in a 2015 report had at least one positive fecal sample, of which 94% were positive for SASd whereas only 1.1% of slaughtered sheep within the United Kingdom were positive for Salmonella, with SASd being the most common isolate.6
A 2017 Swiss report provides additional insight in regard to host factors associated with SASd infection. Three ewes from a herd of 34 ewes and 28 lambs less than 6 months of age developed chronic proliferative rhinitis and eventually died or were euthanized due to respiratory distress. Bacteriological analysis using nasal swabs collected from the remaining members of the flock found 87% of adult sheep were positive for SASd, while all lambs were negative. Possible explanations for this striking difference include: 1) maternal antibody protection; 2) a prerequisite for immunosuppression (e.g. pregnancy); and/or 3) prior or concurrent infection with a yet undetermined organism. This discovery indicates it may be possible to suppress or eliminate SASd from flocks by separating lambs from their dams and other remaining adults prior colonization and infection during their first year of life. However, the feasibility of eradication utilizing this method is purely theoretical and additional investigation is needed.6
References:
1. Bonke R, Wacheck S, Bumann C, et al. High prevalence of Salmonella enterica subsp. diarizonae in tonsils of sheep at slaughter. Food Res Int. 2012 Mar 1;45:880?884.
2. del Carmen Ferreras M, Muñoz M, Pérez V, et al. Unilateral Orchitis and Epididymitis Caused by Salmonella Enterica Subspecies Diarizonae Infection in a Ram. J Vet Diagnostic Investig. 2007;19:194?197.
3. Chatzopoulos DC, Vasileiou NGC, Ioannidi KS, et al. Experimental Study of the Potential Role of Salmonella enterica subsp. diarizonae in the Diarrhoeic Syndrome of Lambs. Pathog (Basel, Switzerland). 2021 Jan 23;10:1?16.
4. Lacasta D, Ferrer LM, Ramos JJ, et al. Chronic Proliferative Rhinitis associated with Salmonella enterica subspecies diarizonae serovar 61:k:1, 5, (7) in Sheep in Spain. J Comp Pathol. 2012 Nov;147:406?409.
5. Rubira I, Figueras L, De las Heras M, et al. Chronic proliferative rhinitis in sheep: An update. Small Rumin Res. 2019 Oct 1;179:21?25.
6. Stokar-Regenscheit N, Overesch G, Giezendanner R, Roos S, Gurtner C. Salmonella enterica subsp. diarizonae serotype 61:k:1,5,(7) associated with chronic proliferative rhinitis and high nasal colonization rates in a flock of Texel sheep in Switzerland. Prev Vet Med. 2017 Sep 15;145:78?82.
7. Uelze L, Borowiak M, Deneke C, et al. Comparative genomics of Salmonella enterica subsp. diarizonae serovar 61:k:1,5,(7) reveals lineage-specific host adaptation of ST432. Microb Genom. 2021;7(8):000604.
