Salmonella PDF

Cattle Medicine (VMED455) Gobena Ameni Veterinary Infectious Diseases and Zoonoses UAEU and AAU, Fall 2024  Salmonellosis Definition Salmonellosis is a disease caused by invasion of salmonella organisms in the intestines, and characterized primarily by septicaem...

Cattle Medicine (VMED455) Gobena Ameni Veterinary Infectious Diseases and Zoonoses UAEU and AAU, Fall 2024  Salmonellosis Definition Salmonellosis is a disease caused by invasion of salmonella organisms in the intestines, and characterized primarily by septicaemia and enteritis. – Extensions from the primary sites Abomasitis Polyarthritis Endarteritis and gangrene of the limbs  Salmonellosis Etiology –Genus Salmonella: Motile Gram-negative Rod-shaped, Fagellated facultative anaerobes, family Enterobacteriaceae  Salmonellosis Etiology – According CDC (USA) the Genus Salmonella contains two species, each of which contains multiple serotypes: 1. Salmonella enterica 2. Salmonella bongori The majority (59%) of the 2463 Salmonella serotypes belong to S. enterica subsp. enteric while the remaining 41% belong to Salmonella bongari – The classification of Salmonella serotypes is based: »flagellar and lipopolysaccharide (LPS) antigens  Salmonellosis Etiology Host specificity – Salmonella enterica serovars: Responsible for most salmonella infections in humans and domesticated animals Serovar-host specificity – The serotypes causing salmonellosis in farm animal species: Cattle: S. typhimurium, S. dublin, Salmonella newport Sheep and goats: S. abortusovis, S. typhimurium, S. dublin, Salmonella anatum Pigs: S. typhimurium, S. choleraesuis Horses: S. typhimurium, S. abortusequi, S. anatum, S. newport, S. enteritidis, Salmonella heidelberg, Salmonella arizona, Salmonella angona.  Salmonellosis Etiology 1) Serovars infecting wide host ranges Example Salmonella typhimurium and Salmonella enteritidis Are ubiquitous in the environment Are usually associated with a relatively mild enteric disease 2) Serovars very restricted to specific host Severe systemic disease in only one host. – Example: Salmonella typhi is restricted to infection in humans, Salmonella abortusovis to infections in sheep, Salmonella abortusequi in horses, Salmonella choleraesuis in pigs.  Salmonellosis Etiology –3) Serovars is associated predominantly with disease in one species but may also infect a limited number of other hosts. Example: S. dublin usually infects cattle but it can also infect other animals, including humans and sheep  Salmonellosis Epidemiology Occurrence – Salmonellosis occurs universally in all species. – Increased incidence of outbreaks of salmonellosis in dairy cattle and humans associated with S. typhimurium definitive type (DT104) in the USA and the UK.  Salmonellosis Epidemiology Occurrence –S. typhimurium definitive type (DT104) This strain is classified as R-type ACSSuT by being resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline. –Extensive drug resistance –Multidrug resistance –Mono-drug resistance  Salmonellosis Epidemiology Morbidity and case fatality – The morbidity rate in outbreaks often can reach 50% or more, – Morbidity and mortality are usually highest in calves under 12 weeks of age, – In all species, the case fatality rate often reaches 100% if treatment is not provided.  Salmonellosis Epidemiology Methods of transmission – Infected animals are the source of the organisms – Infection occurs: Animal-to-animal transmission Contaminated animal feed; and Contaminated environment (soil, birds, rodents, insects, water supplies).  Salmonellosis Epidemiology Carrier state – Salmonellas are facultative intracellular organisms that survive in the phagolysosome of macrophages – Infection can cause a clinical case or lead to a carrier state of infected animals that sheds the organisms constantly or intermittently in feces  Salmonellosis Epidemiology Host risk factors – Newborns are highly susceptible – Adult animals are less susceptible – Susceptibility varies with: Size of the challenge dose Immunological status of the animal (depending on colostrum intake in neonates), Previous exposure to infection, Exposure to stressors, particularly in older animals. Transport, Intercurrent disease  Salmonellosis Epidemiology Environmental and management risk factors Intensification of husbandry in all species Change in management of the herd Intensive pasture utilization ingestion of feed: Housed animals: in large-scale calf rearing units, epidemics can easily occur and cause high morbidity and mortality Contaminated feedstuffs, carrier animals and infected clothing of visitors and casual workers are the most common methods of introducing infection.  Salmonellosis Epidemiology Pathogen risk factors – Salmonellas are relatively resistant to various environmental factors, – They multiply in a pH range of 4 and 8, – Can multiply in an environment with a low level of or no oxygen, – Several serovars are multidrug resistant Example: S. typhimurium DT104 – It is sensitive to pasteurization, – Sensitive to beta-and gamma-irradiation.  Salmonellosis Epidemiology Pathogen risk factors The O-antigen of lipopolysaccharide of salmonellas is toxic and an important virulence factor, The fimbriae mediate a variety of virulence factors important for the maintenance of Salmonella in host immunological cells  Salmonellosis Economic importance Economic losses include: 1. the costs of clinical disease, Reduced weight gains, Poor growth, Reduced milk production 2. Deaths, 3. Diagnosis and treatment of clinical cases, 4. Costs of cleaning and disinfection, and 5. Costs of control and prevention  Salmonellosis Pathogenesis Pathogenicity-host specificity The evolution of host-specific Salmonella serovars is associated with an increase in pathogenicity for the specific host, –Broad host-range serovars (typhimurium and enteritidis) are associated with less severe disease except in young animals, –whereas host-restricted serovars cause high mortality in both young and adult hosts.  Salmonellosis Pathogenesis Septicemic and enteric forms are not mutually exclusive Septicemic form (septicemia and enteritis) 1. Oral infection, 2. Invasion of the mucosa of distal ileum and the cecum 3. Replication in the submucosa ileum and cecum, and in Peyer's patches, 4. Spread to the reticuloendothelial cells of the liver and invasion of the bloodstream, (bacteremia) 5. After invasion of the bloodstream occurs a febrile reaction follows in 24-48 hours, 6. Septicemia (exudative panenteritis), 7. Early septicemia may be rapidly fatal, 8. Survived animals develop carrier state.  Salmonellosis Pathogenesis (other organs) –Abomasitis S. typhimurium DT104 has been associate d with outbreaks of abomasitis in veal calves. –Abortion Second and third trimesters –Terminal dry gangrene, osteitis, and polyarthritis Osteitis is inflammation of bone  Salmonellosis Clinical findings Septicemia – Common in young animals – Profound depression, dullness, collapse, high fever (40.5-42°C) and death within 24-48 hours. – If survived septicemic state, develop severe enteritis, with diarrhea – If survived the enteritis, develop residual polyarthritis or pneumonia  Salmonellosis Clinical findings Acute enteritis – Common in adult animals of all species, – High fever (40 -41°C) – Severe, fluid diarrhea, sometimes, dysentery, – Occasionally tenesmus, – Fever often subsides after onset of diarrhea, – The feces have a putrid smell and contain mucus, sometimes blood, fibrinous casts,  Salmonellosis Clinical Pathology Bacteriological culture: – A definitive etiological diagnosis of salmonellosis depends on culture of the organism from feces, blood, milk, and other body fluids or tissues. Serological tests: – Serological tests are available but lack sensitivity and specificity. Polymerase chain reaction – A PCR assay is a highly specific and sensitive test for the detection of salmonellas in fecal samples from horses. A real-time PCR assay – has relative sensitivity was 100% and specificity 98.2% compared with bacterial culture.  Salmonellosis Necropsy findings Septicemia – But extensive submucosal and subserosal petechial hemorrhages are usually evident. Acute enteritis – Mucoenteritis with submucosal petechiation to diffuse hemorrhagic enteritis, – Severe necrotic enteritis in the ileum and large intestine  Salmonellosis Treatment Primary treatment – antimicrobial therapy Early treatment with broad-spectrum antimicrobials is highly effective in reducing mortality and returning animals to normal function. Fluid and electrolyte therapy A solution of 5% sodium bicarbonate at the rate of 5-8 L per 400 kg BW given intravenously over a period of 2 hours as the initial electrolyte replacement therapy And glucose or fructose administration if the animal is weak  Salmonellosis Control 1. Prevention of introduction of infection (biosecurity), 2. Limitation of spread within a herd, Identify carrier animals and either cull them or isolate and treat them vigorously. 3. Restrict the movement of animals around the farm, 4. The water supply should be provided in troughs that are not susceptible to fecal contamination, 5. Rigorous disinfection of buildings is important. An all-in/all-out policy should be adopted and steam cleaning and chemical sterilization performed after each batch of animals. 6. The control of salmonellosis in veterinary clinics and veterinary teaching hospitals requires special attention to the possible sources of infection and containing and preventing the spread of infection. Farm hygiene and biosecurity  Salmonellosis Control Vaccination – Killed bacterins and live attenuated vaccines are available, – Either can be used as a prenatal vaccine to provide passive immunization of the newborn, – Live Salmonella vaccines are more effective immunogens in calves than killed vaccines.  Salmonellosis Zoonotic importance –Salmonella-contaminated meats and poultry The CDC reports approximately 40,000 confirmed cases of salmonellosis annually in USA, Estimated cost to Americans is about US$1 billion or more annually, the estimate cost of salmonellosis in humans is US$100 million per year in Canada; – this includes hospital and medical costs, lost production, lost leisure, investigating costs and loss of life.  Salmonellosis Zoonotic importance Salmonellae in humans are divided into 1. Typhoidal serotypes: human-restricted invasive typhoidal serotypes Salmonella enterica var typhi [S typhi] Salmonella enterica var paratyphi A [S Paratyphi A]) 2. Non-typhoidal salmonella serotypes Thousands of non-typhoidal salmonella serotypes have a broad vertebrate host range  Salmonellosis Zoonotic importance Salmonella species: 1. Host adapted 2. Host restricted 3. Generalists  Salmonellosis Zoonotic importance Typhoidal serovars: – Human restricted pathogens – Domestic animals are not involved – cause the systemic disease enteric (typhoid) fever – characterized by fever and abdominal pain Serovars Typhi and Paratyphi Typhoid fever Paratyphoid fever  Salmonellosis Zoonotic importance Non-typhoidal Salmonella (NTS): – Enteritidis and typhimurium – Infect a wide range of hosts – Cause acute self-limiting gastroenteritis in humans, cattle, swine and poultry – But can also cause bacteraemia and systemic infections in: Immunosuppressed Hosts, Very young Older individuals Occasionally In healthy adult Humans and animals  Salmonellosis Zoonotic importance Clinical manifestations of NTS infections: Acute gastroenteritis: Bloody stools, Systemic symptoms including fever, chills, myalgias and headache, Vomiting is a less common symptom, Diagnosis is confirmed on stool culture or faecal polymerase chain reaction testing. Septicaemia: Bacteraemia is the most common systemic Salmonella carriage: Chronic carriage is more common in children