BOVINE SALMONELLOSIS: A CHALLENGE TO ONE HEALTH

BOVINE SALMONELLOSIS: A CHALLENGE TO ONE HEALTH

^Rabyia Javed ¹, Rakhi Gangil^2* and Deepak Gangil³

^{1    Dr Rabyia Javed ,Assistant professor Department of veterinary microbiology and immunology} , Sher-e-Kashmir University of Agricultural Sciences and Technology of Jammu (SKUAST)

²Assistant Professor, Department of Veterinary Microbiology, College of Veterinary Sciences and AH MHOW

³Assistant Professor, Department of Veterinary and Animal Husbandry Extension education, College of Veterinary Sciences and AH MHOW

^*Corresponding author: rgangil@gmail.com

Salmonellosis continues to be health problems in man and animals, throughout the world. It is an economic concern of agriculture including dairy industry as well as of modern society. Farmers particularly marginal ones and poor persons keeping one or two dairy animals, suffers a heavy economic loss attributed to treatments, loss of productivity and deaths due to salmonella infection. Society also suffers an economic loss in lost productive days, and in some cases cost incurred because of hospitalization. Salmonellosis in cattle and buffaloes is an economically important disease and is prevalent in many parts of the world. No current discussion of bovine salmonellosis could be complete without acknowledging the increasing public health concern regarding its relevance as an important zoonosis (risk to human health by contaminated dairy and dairy beef products) and increasing antimicrobial resistance among zoonotic enteric pathogens such as Salmonella due to injudicious use of antimicrobials by veterinarians and producers. [1]

Etiology

Salmonella is a genus of gram-negative, facultative anaerobic bacteria that belong to the family of Enterobacteriaceae. There are 2 recognized species within the genus: Salmonella enterica and Salmonella bongori. S. enterica can be further divided into 6 subspecies, S. enterica subspecies enterica being the most relevant in dairy cattle [1]. More than 2500 serovars, differentiated by their antigenic composition, have been identified. Serovars are based on the somatic (O), flagellar (H), and capsular (Vi) antigens. [2]

Seven most frequently Salmonella serotypes isolated from cattle/buffalo in India are: S. typimurium, S. analum, S. dublin, S. weltevreden, S. newport, S. enteritidis and S. richmond. The genus salmonella classified in the family Enterobacteriaceae with the characteristics of straight short rods, gram-negative, usually motile flagella, and aerobic in nature. Salmonella subgroup I includes obligates parasites and pathogens of warm-blooded animal including human beings. Among 2500 salmonella serotypes reported in man and animal about 5-10 serotypes predominate in a country/subcontinent.  Most salmonellae are aerogenic and never produce gas. S. dublin particularly common humans, warm and cold-blooded animals, food and environment. The emergence of S. dublin as one of the most commonly isolated serotypes is of major concern for the dairy industry. As the host-adapted strain of Salmonella in cattle, animals infected with Salmonella dublin can become chronic, subclinical carriers that have the potential to shed large numbers of organisms into the environment. These carriers also play an important role in maintaining infection within a herd by shedding not only in feces, but also in milk and colostrum.

Pathogenesis

Salmonella infections are well-known for their association with clinical signs of enterocolitis, septicemia, and abortion in dairy cattle [3]. Pneumonia is an increasingly common manifestation of Salmonella dublin infection in calves [4,5] and worth bearing in mind when dealing with mild, moderate, or severe respiratory disease on heifer rearing facilities. The most detailed studies of the pathogenesis of bovine salmonellosis infection come from the literature describing enteric infection via the oral route, mainly in calves. [6, 7] Once ingested, Salmonella attaches to mucosal cells and is capable of destroying enterocytes. Attachment is increased if gastrointestinal stasis is present or the normal flora has been disturbed or is not yet established, as is the case in neonates. The organism penetrates through the enterocytes to the lamina propria of the distal small intestine and colon, where they stimulate an inflammatory response or are engulfed by macrophages and neutrophils [1]. Once salmonellae have gained entry to mononuclear phagocytes, they can be rapidly disseminated throughout the body. Salmonellae have a predilection for lymphoid tissues, invading through M-cells, and are found in the highest numbers in the Peyer patches and mesenteric lymph nodes. From here, the organism often enters the lymphatics and may eventually lead to bacteremia [8].

The plasmid bearing strains of S. dublin are highly virulent causing severe enteritis and systemic disease. Probably the virulence plasmid mediates the presence of S.dublin at systemic sites. The virulence of plasmid affected the survival of macrophages in vitro following infection in vivo as assessed by microscopy.

Laboratory diagnosis

Veterinarians working in the field are advised to contact their local diagnostic laboratory for assistance with sample handling, processing, and submission before investigating either individual or group problems with enteric disease suspicious for Salmonella infection. It is frequently worthwhile to place samples directly into enrichment media before submission to improve the chances of positive culture and to keep samples chilled until they arrive at the diagnostic laboratory.

Bacteriological examination

Confirmation of clinical salmonellosis is performed by cultural examination of faeces. Freshly voided faeces are a more reliable material than rectal swab. The technique of isolations make use of selective media like brilliant green agar  modified MacConkey lactose agar of and enrichment media .

Serological Diagnosis

• Serum agglutination test (SAT): A Flagellar titre of 1:320 or higher and somatic titre of 1:40 or higher should be regarded as positive and diagnostic of the carrier state in adult cattle.
• The indirect haemagglutination test: The IHA procedures are generally more sensitive and give higher titre than the somatic SAT.
• Newer techniques for diagnosing Salmonella are based on detection of genetic material from the bacteria i.e. polymerase chain reaction (PCR) techniques. These techniques are generally thought to be more sensitive than culture, but have the disadvantage that subsequent serotyping is not always possible.
• Although fecal culture remains the gold standard at most laboratories, blood culture, a culture of transtracheal wash or bronchoalveolar lavage fluid, and joint fluid may all be useful choices for individuals experiencing bacteremic salmonellosis. The propensity for bacteremia in neonatal calves with salmonellosis makes aseptically obtained aerobic blood cultures a particularly useful diagnostic sample to consider in valuable animals. [1, 8].

Treatment

1. Use of antibiotics: The choice of antibiotics should be based on antibiotic and when sensitivity results are not available the choice should be one of the drugs usually effective against salmonellae. Medication with the water source is most practical.
2. Fluid therapy is the mainstay of treatment for cattle with enteric salmonellosis. In calves with acute, severe diarrhea showing signs of hypovolemic shock, intravenous fluid therapy using a balanced electrolyte solution, such as lactated Ringers, are necessary. In severely depressed or comatose animals, resuscitative fluids, such as hypertonic saline, are indicated.

Prevention and Control

Prevention is not always easy because Salmonellae are widespread in environment and clinically normal carriers occur. The following measures may help to control the infection:

1. Close- herd operations are best when possible.

2.Purchase of replacement stock from herds with no history of   salmonellosis.

3. Quarantine of replacement stock for 2 to 4 weeks.
4. Prevent discharging of effluent from human sewage directly into lots or fields/ calving areas.
5. Hygienic practices eg: cleaning and disinfection of utensils between feeds and of buildings etc.

References:

1. Smith BP. Salmonellosis in ruminants. In: Smith BP, editor. Large animal internal medicine. 4th edition. St. Louis(MO): Mosby; 2009. p. 877–81.
2. Bopp CA, Brenner FW, Fields PI, et al. Escherichia, shigella, and salmonella. In: Murray PR, Baron EJ, Jorgensen JH, et al, editors. Manual of clinical microbiology, vol. 1, 8th edition. Washington, DC: ASM Press; 2003. p. 654–71.
3. Watthiau P, Boland C, Bertrand S. Methodologies for Salmonella enterica subsp. Enterica subtyping, gold standards and new methodologies. Appl Environ Microbiol 2011;77:7877–85.
4. Pecoraro HL, Thompson B, Duhamel GE. Histopathology case definition of naturally acquired Salmonella enterica serovar Dublin infection in young Holstein cattle in the northeastern United States. J Vet Diagn Invest 2017. https://doi.org/10. 1177/1040638717712757.
5. Nielsen LR. Review of pathogenesis and diagnostic methods of immediate relevance for epidemiology and control of Salmonella Dublin in cattle. Vet Microbiol 2013;162(1):1–9.
6. Mohler VL, Heithof DM, Maham MJ, et al. Cross protective immunity conferred by a DNA adenine methylase deficient Salmonella eneterica serovar Typhimurium vaccine in calves challenged with Salmonella serovar Newport. Vaccine 2008; 26(14):1751–8.
7. Tsolis RM, Adams LG, Ficht TA, et al. Contribution of Salmonella typhimurium virulence factors to diarrheal disease in calves. Infect Immun 1999;67(9):4879–85.
8. Wray C, Davies R. Salmonella infections in cattle. In: Wray C, Wray W, editors. Salmonella in domestic animals. New York: CABI Publishing; 2000. p. 169–90.

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