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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
Other Scientific Names
International Common Names
- English: arizona infection in turkeys, chicks, and ducklings; enteric salmonellosis; salmonella enterica serovar gallinarum, fowl typhoid; salmonella in cattle, bovine salmonellosis; salmonella in chickens, avian salmonellosis; salmonella in goats, caprine salmonellosis; salmonella in pigs, swine salmonellosis; salmonella in sheep, ovine salmonellosis; Salmonella infections; salmonella typhimurium in birds, paratyphus
Pathogen/sTop of page Salmonella
Salmonella enterica subsp. diarizonae
OverviewTop of page
The genus Salmonella comprises a large group of bacteria that cause infectious diseases of mammals, birds, fish and reptiles, as well as humans. These organisms are responsible for significant morbidity and mortality in all domestic animals, particularly in young and pregnant animals. Salmonella organisms, therefore, pose a serious threat to animal and food industries. The disease is commonly referred to as salmonellosis, although the term paratyphoid may be used (for example, swine paratyphoid) or pullorum disease (S. pullorum) and fowl typhoid (S. gallinarum) in poultry. The disease has been recognized in all countries, but appears to be most prevalent in areas with intensive systems of animal production. Importation of animal feeds in large quantities to countries with intensive systems of animal production has resulted in widespread international outbreaks of salmonellosis (S. agona) in both animals and humans.
Recent gene-sequencing analyses have indicated that Salmonella and Escherichia coli might have diverged from a common ancestor 120-160 million years ago, coincident with the origin of mammals (Selander et al., 1996). In 1880, Eberth observed the typhoid bacillus in spleen sections and mesenteric lymph nodes of a patient that died from typhoid. In 1886, Salmon and Smith isolated S. choleraesuis from pigs. Since then, more than 2400 different Salmonella serovars have been identified. New serovars are being described each year.
The genus Salmonella is a member of the family Enterobacteriaceae. The scheme for classification of Salmonella organisms has been modified several times in recent years. The full nomenclature is still complicated and cumbersome, and as a consequence, the binominal nomenclature has been widely used, based on recommendations of the International Code of Nomenclature of Bacteria for recognition of a genomic species. According to these recommendations, the genus Salmonella is divided into two species, S. enterica and S. bongory. S. enterica is further divided into six subspecies (S. enterica subsp. enterica, S. enterica subsp. salamae, S. enterica subsp. arizonae, S. enterica subsp. diarizonae, S. enterica subsp. houtenae and S. enterica subsp. indica). Although this nomenclature is not yet validated, it is scientifically based and less confusing than other proposals. Serovar names are no longer considered as species names. For example, S. typhimurium is now called S. enterica subsp. enterica serovar Typhimurium, although some researchers still prefer to use the simpler form Salmonella serovar Typhimurium (or Salmonella Typhimurium). Only serovars of S. enterica subsp. enterica are given names (usually based on the name of geographic location of their first isolation). Other serovars are identified only by the subspecies, followed by their O: H antigenic formula.
Fowl typhoid (S. gallinarum), pullorum disease (S. pullorum) and salmonellosis (S. abortusovis) are on the list of diseases notifiable to the World Organisation for Animal Health (OIE). For further information on theses diseases from OIE, see the website: www.oie.int.
Host AnimalsTop of page
|Animal name||Context||Life stage||System|
|Alectoris rufa (red-legged partridge)||Domesticated host, Wild host|
|Anas (ducks)||Domesticated host, Wild host||Poultry: All Stages|
|Bos grunniens (yaks)|
|Bos indicus (zebu)||Domesticated host||Cattle & Buffaloes: All Stages|
|Bos taurus (cattle)||Domesticated host||Cattle & Buffaloes: All Stages|
|Camelus dromedarius (dromedary camel)||Domesticated host|
|Capra hircus (goats)||Domesticated host, Wild host||Sheep & Goats: All Stages|
|Cavia porcellus (domesticated guinea pig)|
|Equus||Domesticated host, Wild host||Other: All Stages|
|Gallus||Domesticated host, Wild host||Poultry: All Stages|
|Gallus gallus domesticus (chickens)|
|Meleagris||Domesticated host, Wild host||Poultry: All Stages|
|Meleagris gallopavo (turkey)|
|Ovis aries (sheep)||Domesticated host, Wild host||Sheep & Goats: All Stages|
|Perdix perdix (grey partridge)||Domesticated host, Wild host|
|Phasianus colchicus (common pheasant)|
|Sturnus vulgaris (common starling)|
|Sus scrofa (pigs)||Domesticated host, Wild host||Pigs: All Stages|
Hosts/Species AffectedTop of page
Salmonella strains can be classified according to their adaptation to animal and human hosts. Certain Salmonella serovars show remarkable host specificities. This group includes: S. dublin in cattle, S. choleraesuis and S. typhisuis in pigs, S. pullorum and S. gallisepticum in poultry, and S. abortusovis and S. arizonae in sheep, as well as S. typhi and S. paratyphi A, which cause enteric fever only in humans and higher primates. However, most Salmonella serovars are non-host specific, and cause disease in many animal species and humans, of which S. typhimurium and S. enteritidis are most common.
The incidence of salmonellosis has increased with the intensification of livestock production. Factors such as transportation of animals, overcrowding, administration of corticosteroids, parturition, and concurrent viral and protozoan infections have all been shown to increase susceptibility of animals to disease. Infections such as Chlamydia psittaci in sheep, Fasciola hepatica in cattle or bovine diarrhoea virus in calves may aggravate Salmonella infections. Feeding changes that affect the intestinal flora, which is normally inhibitory to colonization by Salmonella, may modulate the susceptibility to the organism. Housing may also influence the numbers of infected birds within a flock. Kindle et al. (1996) investigated the prevalence of Salmonella during an outbreak in chickens and found a lower prevalence of S. enteritidis PT4 among caged hens than among free-range hens (1.7 vs. 50%).
Systems AffectedTop of page blood and circulatory system diseases of large ruminants
blood and circulatory system diseases of pigs
blood and circulatory system diseases of poultry
blood and circulatory system diseases of small ruminants
digestive diseases of large ruminants
digestive diseases of pigs
digestive diseases of poultry
digestive diseases of small ruminants
nervous system diseases of large ruminants
nervous system diseases of pigs
nervous system diseases of poultry
nervous system diseases of small ruminants
reproductive diseases of large ruminants
reproductive diseases of pigs
reproductive diseases of poultry
reproductive diseases of small ruminants
respiratory diseases of large ruminants
respiratory diseases of pigs
respiratory diseases of poultry
respiratory diseases of small ruminants
skin and ocular diseases of large ruminants
skin and ocular diseases of pigs
skin and ocular diseases of poultry
skin and ocular diseases of small ruminants
DistributionTop of page
Salmonellosis is caused by a large group of bacteria, which are widespread in nature, do not recognize international borders, and only few serotypes show host specificity. The disease has been identified in all countries, but it is most prevalent in countries with intensive animal production systems, particularly of poultry and pigs (e.g. North America and Western Europe). In 1995, the World Health Organization conducted a survey involving 69 member countries that used Salmonella serotyping as a part of public health surveillance, and found that S. enteritidis was the most common isolate in 35 countries, followed by S. typhi in 12 countries, and S. typhimurium in 8 countries.
Fowl typhoid (S. gallinarum), pullorum disease (S. pullorum) and salmonellosis (S. abortusovis) are on the list of diseases notifiable to the World Organisation for Animal Health (OIE). To find out the current distribution of these diseases, see OIE's WAHID database on disease occurrence.
PathologyTop of page
Postmortem findings in carcasses of animals that die of salmonellosis are variable. In poultry, postmortem lesions may include dehydration, emaciation, enteritis (often in the form of typhlitis), diarrhoea and purulent arthritis. Histopathological findings in birds often include necrotic foci in the liver, enlarged lymphoid tissue in the lamina propria and submucosa of the duodenum, ileum, caeca and colon. Salmonella are more frequently isolated from the caeca than from any other organ or tissue. The spleen, liver and kidneys are also frequently positive for Salmonella organisms. In pigs that die of the septicaemic form of salmonellosis, gross lesions include colitis, infarctions of gastric mucosa, swollen mesenteric lymph nodes, splenomegaly, hepatomegaly and lung congestion. Histopathological examination of pigs that die of salmonellosis often reveals a paratyphoid nodule in the liver. Postmortem lesions in cattle often include an acute enteritis, particularly of the ileum and large intestine, and sometimes the mesenteric lymph nodes are enlarged. However, these lesions are insufficient to make a conclusive diagnosis. Extensive submucosal and subserosal petechial haemorrhages are often found in calves dying of acute septicaemia. The liver commonly shows jaundice, the mesenteric lymph nodes are oedematous and enlarged, and the small intestine shows a diffuse mucoid enteritis. In sheep that die of septicaemic salmonellosis, usual findings include acute enteritis, splenic enlargement, congested organs and severe abomasitis. Inflammatory changes in the caecum and colon may also be detected. Histological examination of aborted fetuses reveals hyperaemia, oedema and haemorrhages in many organs.
DiagnosisTop of page
The clinical signs and lesions are not pathognomonic, and in many cases, particularly in poultry and pigs, Salmonella infection may be inapparent. The course of infection, clinical signs and postmortem findings depend on different factors, such as the Salmonella serovar, the species and age of affected animals. The most common clinical manifestation of salmonellosis is enteritis, although septicaemia, genital infections with abortion, and arthritis often occur.
Salmonella infection is a major cause of cattle morbidity and mortality and S. typhimurium and S. dublin are the serotypes most frequently isolated from diseased cattle.
Bovine salmonellosis is most common in calves, but can occur at any age, particularly after stress. Diagnosis is by isolation of the organism from faeces or rectal mucosa. Abortion may follow infection and organism can be isolated from the faeces. Salmonellosis in cattle can cause septicaemia, especially in calves, with sloughing of the skin of extremities in rare cases. Disease in calves occurs after 1 week of age, and meningitis may occur. This is a zoonosis.
Salmonella also cause clinical diseases in sheep, which are most commonly associated with subspecies S. diarizonae and S. typhimurium. Abortion may be the only sign of infection with S. abortusovis or S. montevideo in ewes, but other types cause clinical signs in other body systems. The diarrhoeic form of salmonellosis is transmitted to lambs from infected mothers or other sources. In addition to acute disease, a chronic recurring form of salmonellosis has also been known to occur.
Salmonellosis in pigs (swine salmonellosis) is usually characterized by enterocolitis or septicaemia, although pneumonia associated with S. choleraesuis may be seen without enterocolitis or septicaemia. Enterocolitis can be acute or chronic, and most frequently is seen in pigs from weaning to about 4 months of age. S. choleraesuis is the most common isolate in USA, followed by S. typhimurium, S. derby and S. agona. Cervical lymphadenitis can be seen in affected pigs. Septicaemic salmonellosis mainly affects weaned piglets less than 4 months of age, but is also seen occasionally in adult pigs. Diarrhoea can be seen at later stages of infection. Outbreaks of salmonellosis in which meningitis was the main or only sign have also been described. This is a zoonotic disease.
Salmonella in goats has been reported as a cause of abortion, but also can cause the diarrhoeic and septicaemic conditions seen in other domestic animals. Kids, young animals or adult goats are affected. Diagnosis is by culture. Haemorrhagic faeces are less common in goats with salmonellosis than in other animals. Signs may become chronic with recurrences.
S. typhimurium and several other serotypes of Salmonella are common causes of disease in poultry and other birds, usually in chicks. Avian salmonellosis caused by S. enteritidis affects chickens and pheasants, but does not seem to affect fertility, hatchability or egg production. It can cause clinical disease in chicks less than 1 week of age. S. enteritidis infection in older broilers causes unevenness and stunting. Pullorum disease is caused by S. pullorum in all birds, but chickens, turkeys and pheasants are most commonly affected. The disease is seen primarily in chicks less than 3 weeks of age or in-shell chicks. It is rare in adult birds, but can cause decreased productivity and is often transmitted through the hatching egg. Fowl typhoid is an infectious disease caused by S. gallinarum, which primarily affects chickens and turkeys, but occasionally other poultry, game and wild birds become infected. Fowl typhoid has many of the clinical and epizootiological features and lesions that are seen in birds with pullorum disease. The disease is most common in chickens and turkeys and often persists for months. Fowl typhoid may also occur in growing birds with no previous history of infection. Transmission is through eggshell contamination and through contaminated feed. Adult carriers also shed the organism in their faeces. Nodules in the lung, liver, gizzard, heart, intestinal wall, spleen and peritoneum characterize lesions in chicks. Petechial haemorrhages or foci of necrosis and swollen joints are occasionally seen. If lesions are present in adult birds, they include nodular myocarditis, pericarditis, haemorrhagic ovaries and ascites. Diagnosis is by history, agglutination test and isolation of the organism.
Clinical signs and lesions are of little diagnostic value. Diagnosis is based on the isolation of the organism from tissue samples, faeces, rectal swabs or environmental samples using cultural methods. Numerous cultural methods for the isolation of Salmonella have recently been reviewed (Barrow, 1995; Tietjen and Fung, 1995). Suspected colonies should be sub-cultured on to selective and non-selective agars to exclude possible contaminants. Accurate diagnosis must be supported with biochemical identification of the isolate or detection of antibodies using serological techniques. Various biochemical and serological tests can be used to confirm diagnosis. The methylumbelliferyl caprylate fluorescence test (MUCAP) is an easy and rapid method for screening suspected Salmonella colonies. Direct slide agglutination test and specific antisera are used for the determination of the O and H antigens and, sometimes, the Vi antigen. Additional biochemical tests, such as maltose and dulcitol tests, may be needed to identify some serotypes. Antimicrobial sensitivity to a range of agents should also be tested. Common serotypes can be identified in most laboratories, whereas for information on the genetic profile and phage type, reference laboratories may need to be consulted. Several alternative systems and test kits have been derived from conventional diagnostic techniques to save time and consumables requirements and improve overall performance of the Salmonella screening procedures. These methods include polymerase chain reaction, nucleic-acid-based assays, immunological techniques and electrical conductance and impedance (Blackburn, 1993; Giese, 1995; Feng, 1996; Patel, 1997), and they generally can be completed within 24-52 hours. Immunological techniques for detecting Salmonella include immunoagglutination, immunoprecipitation, immunocapture, enzyme-linked immunosorbent assays (ELISA), enzyme-linked immunofluorescent assays (ELFA) and immunodiffusion. Most of the immunological and other alternative tests have detection limits of 102-105 cells/ml and therefore require pre-enrichment and/or selective enrichment for at least 16-24 h. These assays are generally more difficult to perform than conventional cultural methods. Fully automated methods are also available, but they require additional investments in instruments and consumables, and as such are costly.
List of Symptoms/SignsTop of page
|Cardiovascular Signs / Tachycardia, rapid pulse, high heart rate||Cattle & Buffaloes:All Stages,Sheep & Goats:All Stages||Sign|
|Digestive Signs / Abnormal colour of stool in birds, white, green, yellow faeces||Poultry:All Stages||Sign|
|Digestive Signs / Anal, rectal stricture||Sign|
|Digestive Signs / Anorexia, loss or decreased appetite, not nursing, off feed||Cattle & Buffaloes:All Stages,Poultry:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|Digestive Signs / Bloody stools, faeces, haematochezia||Cattle & Buffaloes:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|Digestive Signs / Congestion oral mucous membranes, erythema, redness oral mucosa||Cattle & Buffaloes:All Stages||Sign|
|Digestive Signs / Dark colour stools, faeces||Sheep & Goats:All Stages||Sign|
|Digestive Signs / Diarrhoea||Cattle & Buffaloes:All Stages,Poultry:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|Digestive Signs / Mucous, mucoid stools, faeces||Cattle & Buffaloes:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|Digestive Signs / Rumen hypomotility or atony, decreased rate, motility, strength||Sheep & Goats:All Stages||Sign|
|Digestive Signs / Unusual or foul odor, stools, faeces||Cattle & Buffaloes:All Stages,Sheep & Goats:All Stages||Sign|
|Digestive Signs / Vomiting or regurgitation, emesis||Pigs:All Stages||Sign|
|General Signs / Ataxia, incoordination, staggering, falling||Pigs:All Stages||Sign|
|General Signs / Cyanosis, blue skin or membranes||Cattle & Buffaloes:All Stages,Pigs:All Stages||Sign|
|General Signs / Dehydration||Cattle & Buffaloes:All Stages,Poultry:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|General Signs / Dysmetria, hypermetria, hypometria||Pigs:All Stages||Sign|
|General Signs / Exercise intolerance, tires easily||Poultry:All Stages||Sign|
|General Signs / Fever, pyrexia, hyperthermia||Cattle & Buffaloes:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|General Signs / Forefoot swelling, mass front foot, feet||Cattle & Buffaloes:All Stages||Sign|
|General Signs / Forelimb lameness, stiffness, limping fore leg||Cattle & Buffaloes:All Stages||Sign|
|General Signs / Forelimb swelling, mass in fore leg joint and / or non-joint area||Sign|
|General Signs / Generalized lameness or stiffness, limping||Cattle & Buffaloes:All Stages||Sign|
|General Signs / Generalized weakness, paresis, paralysis||Cattle & Buffaloes:All Stages,Poultry:All Stages,Sheep & Goats:All Stages||Sign|
|General Signs / Hindlimb lameness, stiffness, limping hind leg||Cattle & Buffaloes:All Stages||Sign|
|General Signs / Hindlimb swelling, mass in hind leg joint and / or non-joint area||Cattle & Buffaloes:All Stages||Sign|
|General Signs / Icterus, jaundice||Cattle & Buffaloes:All Stages,Pigs:All Stages||Sign|
|General Signs / Inability to stand, downer, prostration||Pigs:All Stages||Sign|
|General Signs / Increased mortality in flocks of birds||Poultry:All Stages||Sign|
|General Signs / Lack of growth or weight gain, retarded, stunted growth||Cattle & Buffaloes:All Stages,Poultry:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|General Signs / Lameness, stiffness, stilted gait in birds||Sign|
|General Signs / Lymphadenopathy, swelling, mass or enlarged lymph nodes||Pigs:All Stages||Sign|
|General Signs / Neck swelling, mass cervical region||Pigs:All Stages||Sign|
|General Signs / Opisthotonus||Cattle & Buffaloes:All Stages||Sign|
|General Signs / Pale comb and or wattles in birds||Poultry:All Stages||Sign|
|General Signs / Pale mucous membranes or skin, anemia||Sign|
|General Signs / Pale mucous membranes or skin, anemia||Sign|
|General Signs / Pale mucous membranes or skin, anemia||Sign|
|General Signs / Polydipsia, excessive fluid consumption, excessive thirst||Poultry:All Stages||Sign|
|General Signs / Regression of the comb, wattles in birds||Poultry:All Stages||Sign|
|General Signs / Reluctant to move, refusal to move||Cattle & Buffaloes:All Stages,Poultry:All Stages,Pigs:All Stages||Sign|
|General Signs / Sudden death, found dead||Cattle & Buffaloes:All Stages,Poultry:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|General Signs / Swelling of the limbs, legs, foot, feet, in birds||Poultry:All Stages||Sign|
|General Signs / Swelling, mass, wing||Poultry:All Stages||Sign|
|General Signs / Torticollis, twisted neck||Poultry:All Stages||Sign|
|General Signs / Trembling, shivering, fasciculations, chilling||Poultry:All Stages,Pigs:All Stages||Sign|
|General Signs / Underweight, poor condition, thin, emaciated, unthriftiness, ill thrift||Cattle & Buffaloes:All Stages,Poultry:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|General Signs / Weakness, paresis, paralysis of the legs, limbs in birds||Sign|
|General Signs / Weakness, paresis, paralysis of the legs, limbs in birds||Sign|
|General Signs / Weakness, paresis, paralysis, drooping, of the wings||Poultry:All Stages||Sign|
|General Signs / Weight loss||Cattle & Buffaloes:All Stages,Poultry:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|Nervous Signs / Abnormal behavior, aggression, changing habits||Pigs:All Stages||Sign|
|Nervous Signs / Circling||Pigs:All Stages||Sign|
|Nervous Signs / Coma, stupor||Cattle & Buffaloes:All Stages||Sign|
|Nervous Signs / Dullness, depression, lethargy, depressed, lethargic, listless||Cattle & Buffaloes:All Stages,Poultry:All Stages,Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|Nervous Signs / Propulsion, aimless wandering||Pigs:All Stages||Sign|
|Nervous Signs / Seizures or syncope, convulsions, fits, collapse||Cattle & Buffaloes:All Stages||Sign|
|Nervous Signs / Tremor||Pigs:All Stages||Sign|
|Ophthalmology Signs / Blindness||Poultry:All Stages||Sign|
|Ophthalmology Signs / Chemosis, conjunctival, scleral edema, swelling||Poultry:All Stages||Sign|
|Ophthalmology Signs / Conjunctival, scleral, injection, abnormal vasculature||Cattle & Buffaloes:All Stages||Sign|
|Ophthalmology Signs / Conjunctival, scleral, redness||Cattle & Buffaloes:All Stages||Sign|
|Ophthalmology Signs / Corneal edema, opacity||Poultry:All Stages||Sign|
|Ophthalmology Signs / Corneal swelling, mass, nodule||Poultry:All Stages||Sign|
|Ophthalmology Signs / Hypopyon, lipid, or fibrin, flare, of anterior chamber||Poultry:All Stages||Sign|
|Ophthalmology Signs / Nystagmus||Pigs:All Stages||Sign|
|Pain / Discomfort Signs / Colic, abdominal pain||Sign|
|Reproductive Signs / Abortion or weak newborns, stillbirth||Cattle & Buffaloes:Heifer,Cattle & Buffaloes:Cow,Pigs:Gilt,Pigs:Sow,Sheep & Goats:Gimmer,Sheep & Goats:Mature female||Sign|
|Reproductive Signs / Agalactia, decreased, absent milk production||Cattle & Buffaloes:Cow,Sheep & Goats:Mature female||Sign|
|Reproductive Signs / Decreased hatchability of eggs||Poultry:Mature female||Sign|
|Reproductive Signs / Decreased, dropping, egg production||Poultry:Mature female||Sign|
|Reproductive Signs / Female infertility, repeat breeder||Sheep & Goats:Mature female||Sign|
|Reproductive Signs / Mastitis, abnormal milk||Cattle & Buffaloes:Cow||Sign|
|Respiratory Signs / Coughing, coughs||Pigs:All Stages||Sign|
|Respiratory Signs / Dyspnea, difficult, open mouth breathing, grunt, gasping||Cattle & Buffaloes:All Stages,Poultry:All Stages,Pigs:All Stages||Sign|
|Respiratory Signs / Increased respiratory rate, polypnea, tachypnea, hyperpnea||Cattle & Buffaloes:All Stages,Poultry:All Stages||Sign|
|Respiratory Signs / Mucoid nasal discharge, serous, watery||Cattle & Buffaloes:All Stages||Sign|
|Respiratory Signs / Purulent nasal discharge||Cattle & Buffaloes:All Stages||Sign|
|Skin / Integumentary Signs / Alopecia, thinning, shedding, easily epilated, loss of, hair||Cattle & Buffaloes:All Stages||Sign|
|Skin / Integumentary Signs / Cold skin, cool ears, extremities||Sign|
|Skin / Integumentary Signs / Moist skin, hair or feathers||Cattle & Buffaloes:All Stages||Sign|
|Skin / Integumentary Signs / Rough hair coat, dull, standing on end||Pigs:All Stages,Sheep & Goats:All Stages||Sign|
|Skin / Integumentary Signs / Ruffled, ruffling of the feathers||Poultry:All Stages||Sign|
|Skin / Integumentary Signs / Skin necrosis, sloughing, gangrene||Cattle & Buffaloes:All Stages,Pigs:All Stages||Sign|
|Skin / Integumentary Signs / Soiling of the feathers, vent feathers||Poultry:All Stages||Sign|
|Skin / Integumentary Signs / Soiling of the vent in birds||Poultry:All Stages||Sign|
|Urinary Signs / Polyuria, increased urine output||Sign|
Disease CourseTop of page
There are three major forms of salmonellosis in animals: enteritis, septicaemia and abortion, but all combinations of the three forms have been observed in susceptible animals. Enteritis can have acute, subacute or chronic forms. Acute enteritis is the common form in adult animals, but can also occur in calves under 1 week of age. In affected animals, there is fever (40.5-41.5°C) initially, followed by severe diarrhoea, sometimes dysentery and often tenesmus. Subacute enteritis can occur in adult sheep and cattle. The main clinical signs include fever (39-40°C), soft faeces and dehydration. A high incidence of abortion is common in cows and ewes with subacute enteritis. Chronic enteritis is common in adult cattle and pigs. Affected animals have persistent diarrhoea, intermittent fever and are emaciated.
Septicaemia is the most severe form of salmonellosis and is the usual syndrome in newborn animals, but can occur in pigs up to 6 months of age. The septicaemic form may be severe with an acute course, which is highly fatal if untreated, or milder with a subacute course and a slow resolution.
Abortion often occurs in pregnant animals with the septicaemic form of salmonellosis. Outbreaks of abortion in cattle have been associated with S. dublin infections, but several other host-specific serovars are also associated.
Poultry are often infected with Salmonella, but disease usually does not develop, so poultry are one of the primary reservoirs of the organism. Clinical disease is frequent in cattle, sheep and pigs. However, pigs are also frequently healthy carriers.
EpidemiologyTop of page
Members of the genus Salmonella are often referred to as universal pathogens because of their ubiquitous presence in nature. Salmonella are recovered from almost all vertebrates and some insects (Taylor and McCoy, 1969; Falkow and Mekalanos, 1990). Salmonella inhabits the intestinal tract of a wide range of animals, such as mammals, birds, fish and reptiles. Their excretions contaminate water, food and the environment. Salmonella are commonly found in farm effluents, human sewage and in any materials exposed to faecal contamination. Because of their widespread presence in the environment, some scientists consider Salmonella to be primarily an environmental organism that is pathogenic for animals.
Transmission and spread of Salmonella occurs by vertical and horizontal routes, or both. Vertical transmission occurs in poultry when Salmonella infects follicles in the ovary, or the developing eggs become infected in the oviduct. Other forms of shell contamination can also be a problem. Horizontal transmission occurs on farms by direct contact between infected and uninfected animals, or by indirect contact via contaminated environments. One of the commonest sources for horizontal transmission of infection is feed that contains Salmonella. Fertilizers and feeds containing animal products are sometimes contaminated. The organism occurs most frequently in fish meal, bone meal and meat meal. Contaminated milk and milk products are also important sources of Salmonella infection, particularly in calves. Hatcheries are one of the major sources of horizontal transmission in poultry because Salmonella can survive for long periods in eggshells, dust and litter.
Poultry and many other animals that are often latently infected without showing clinical diseases are important in spreading infection to other animals. Such animals excrete Salmonella intermittently in their faeces and form a large reservoir and source of contamination for healthy animals, humans and the environment. Significant reservoirs for Salmonella are humans, farm animals, pigeons, waterfowl and wild birds. Rodents, pets and insects are also potential reservoirs and they can transmit the infection. Salmonella are readily transferred from animal to animal, animal to humans, humans to animals, and human to human by direct and indirect pathways.
Impact: EconomicTop of page
Salmonella is recognized as an important zoonotic pathogen of worldwide economic significance. In 1987, the annual cost of various measures to control mortality and morbidity from Salmonella infections in the US turkey industry was estimated at approximately $US 10 million (Pomeroy et al., 1989). Wray and Linklater (2000) considered the number of incidents of Salmonella infections in sheep (100 to 200 cases annually) and the size of the UK sheep population and concluded that ovine salmonellosis is of much less economic importance than salmonellosis in other species of farm animals. The economic costs of salmonellosis in humans are even higher. $US 1 billion was lost in the USA in 1987 because of absence from work and medical treatment of salmonellosis (Roberts, 1988). Salmonellosis is also a major cause of economic losses in pig production, resulting in millions of $US in lost income (Schwartz, 1990). Estimated costs per reported case of human salmonellosis in North America and Europe range from $US 1000 to $US 3000 (World Health Organization, Fact Sheet No 139, 1997), and the total annual cost of salmonellosis in the USA is estimated to be $US 4000 million. The annual cost of foodborne diseases, primarily salmonellosis, in the UK, as announced in the UK Food and Drink Federation’s 1994 report, amounted to approximately $1500 million.
Zoonoses and Food SafetyTop of page
The prevalence of Salmonella infection in both humans and domestic animals has increased markedly in recent years. This increase may be explained by rapid intensification of animal production in developed countries, which has resulted in marked changes in food distribution and eating habits of the human population. Chicken meat has become the cheapest source of animal protein in Western Europe and North America.
A number of foods of animal origin can harbour Salmonella (e.g. pork, beef and poultry meat, eggs and milk). Humans mainly contract salmonellosis through the consumption of improperly cooked meat or raw foods of animal origin contaminated with faeces or by handling infected animals. Salmonella infections of cattle and sheep, as well as those of pets, such as dogs and cats, have the potential to cause disease in humans by direct contact with the infected animal. S. typhimurium and S. enteritidis are most common causes of zoonotic salmonellosis in many countries. Although S. enteritidis is mainly associated with poultry and eggs, S. typhimurium can be found in a wide range of foods, such as meat from poultry and other animals, meat products and unpasteurized milk. Human-to-human transmission is uncommon in developed countries, but can occur in institutions such as baby care units, hospitals and residential homes for the elderly.
Salmonella frequently causes mild food poisoning in humans, which resolves without treatment in most cases, but occasionally Salmonella can cause severe septicaemic diseases, which require prompt and vigorous treatment with antimicrobial drugs.
Disease TreatmentTop of page
Treatment with antimicrobial drugs is effective in reducing mortality and the environmental contamination during outbreaks of salmonellosis. Intravenous and oral fluid and electrolyte therapy increases the survival rate in cattle. Intravenous hypertonic saline (4 mg/kg of 7% NaCl) combined with oral rehydration with water or hypotonic sodium-containing fluid via a stomach tube has proved particularly useful in cattle. Injections of tetracyclines, streptomycin, apramycin, neomycin, ampicillin, amoxycillin, spectinomycin, trimethoprim-sulfonamide, enrofloxacin, danofloxacin and chloramphenicol (except in the UK due to resistance) are all effective in treatment. However, infected animals may remain carriers after treatment. Medication may also be administered to animals with unaffected appetite in feed. If animals fail to respond to antimicrobial treatment, the choice of drugs to be used depends on antimicrobial sensitivity testing of isolates, because some Salmonella isolates may be resistant to different drugs.
Multiple drug resistance is common in Salmonella, but there are variations in the predominant patterns among isolates from different countries, and from different animal species. The majority of Salmonella strains isolated from pigs show resistance to at least one antimicrobial agent. S. typhimurium is commonly resistant to several drugs and the resistance is often plasmid-encoded (Clarke and Gyles, 1993). Since the 1990s, the incidence of multiple resistance in strains of S. typhimurium increased worldwide, but particularly in those isolated in England and Wales. The reason for worldwide dissemination of multi-resistant S. typhimurium DT104 are unclear; however, resistance to ciprofloxacin (fluoroquinolone) in S. virchow and S. hadar and the occurrence of multi-drug resistance in S. typhimurium DT104 increased significantly following the licensing of enrofloxacin and danofloxacin (fluoroquinolones) for veterinary use in the UK in 1993 and 1996, respectively. The most resistant strains come from developed countries due to indiscriminate use of antimicrobial agents, usually as growth promoters, in animals destined for human consumption.
Resistance of various Salmonella strains to streptomycin, tetracycline and sulfonamides is very common, resistance to ampicillin, kanamycin, neomycin and chloramphenicol is common, and resistance to fluoroqinolones, third-generation cephalosporins, gentamicin and ampicillin- or ticarcillin combination with beta-lactamase inhibitors is rare.
Prevention and ControlTop of page
A number of live inactivated vaccines, which may protect against clinical disease, if given at least 2 weeks before exposure to Salmonella organisms, have been described. See the 'Drugs Database' in the AHPC for more information about some Salmonella vaccines. These vaccines are effective against host-specific Salmonella serovars, but they are less effective against intestinal colonization in pigs, chickens and calves with host non-specific serovars. Salmonella organisms for use in vaccine production are usually inactivated using heating or formalin. More recently, molecular biology techniques have been used to manufacture mutant vaccines, which are now available in Germany, the USA and other countries for use in poultry, pigs and other species of domestic animals. Recent advances in the development of adjuvants, such as microspheres, which are potent immunostimulants (Morein et al., 1996), may lead to production of the next generation of Salmonella subunit vaccines. Meanwhile, the use of autogenous vaccines may be a cheaper alternative for countries with limited resources than purchase of commercially available vaccines of dubious efficacy.
The major strategy for the control of Salmonella should include the following measures: cleaning the production chain from the top, feed hygiene, feed additives, competitive exclusion, vaccination, education programmes, hygienic measures and eradication. Although difficult, eradication of Salmonella may be possible by complete depopulation, or by treatment of whole herd or flock combined with disinfection.
Salmonellosis is a notifiable disease in many countries, which have national schemes to control the disease in animals, and is subject to compulsory control measures. In the European Union, monitoring of breeding flocks of more than 250 birds and hatcheries for S. enteritidis and S. typhimurium is regulated by the Zoonoses Directive 92/117/EEC (European Union, 1992).
Fowl typhoid (S. gallinarum), pullorum disease (S. pullorum) and salmonellosis due to S. abortusovis are on the list of diseases notifiable to the World Organisation for Animal Health (OIE). Suspected cases should be reported to veterinary services and then to state animal health services.
Salmonella control in pig production is difficult and costly, but progress can be made by introducing effective monitoring programmes, all in/all out production where possible, effective cleaning and disinfection and rodent control in post-weaning accommodation to ensure that the breeding pyramid remains free of important zoonotic infections such as S. typhimurium DT104. Investigation of feeding methods that may reduce colonization of the intestine by Salmonella is required, as well as investigations of the presence of Salmonella in clinically healthy animals which is at present unknown. S. typhimurium and S. derby are the predominant serotypes in pig herds with clinical disease, but the majority of herd infections are subclinical and little is known about the level of Salmonella carriage in healthy pigs.
Biosecurity measures such as rodent and fly control and housing livestock on wild-bird-proof farms may help prevent the introduction of salmonellosis to healthy herds or flocks. The importance of protecting feed stores from contamination by wildlife droppings, in particular, has been recognized. Isolation of infected animals, the use of salmonella-free stock, clean feed and water, are also important in prevention and control of salmonellosis.
ReferencesTop of page
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