Mortality And Morbidity Caused By Salmonella Biology Essay


Globally, the mortality and morbidity caused by Salmonella will continue to be a problem for the health of the public. Salmonella typhi exclusively induce diseases in humans and it is the causative agent of typhoid fever (Prouty and Gunn 2003, 7154-7158). It is referred to as an obligate parasite.

About 17 million people are affected by typhoid fever yearly resulting in closely 600 000 deaths all over the world.

Historically, Salmonella typhi has led to the death of different renowned figures including Wilbur Wright who invented the airplane and Rudyard Kipling (a British author and poet). Salmonella typhi was isolated by Karl J. Erberth in 1880 and it is mostly found in developing countries with lack of antibiotics and poor sanitary systems (David 2003).

In Malaysia, typhoid is a known disease and for the years 1964 to 1976, the average number of cases reported is about one thousand yearly which is exceptional of one or two years that the average number increased. The number of cases reported yearly varies from 8 to 5 to 12 to 7 per the population of 100000 despite the activities conducted to eradicate the disease.

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Typing scheme of Vi phage has been the technique recognized for epidemiological finger printing of the strains of Salmonella typhi. Results gotten from typing of phage has aided tracing of the transmission route and discovery of the source of infection.

The Bacteriology Division of the Institute for Medical Research, Kuala Lumpur,

Malaysia, began Vi-phage typing of Salmonella typhi in 1971 with the positioning of the Salmonella typhi Vi-phage Typing National Centre to help in the control of the diseases. This was done with the assistance of Dr. E. S. Anderson (Director, International Reference Laboratory for Enteric Phage Typing, Colindale) and the World Health Organisation.

Certain degree of immunity can be conferred on people infected with Salmonella typhi or Salmonella paratyphi and there is milder occurrence of re-infection. The circulation of Vi and O antibodies are linked with resistance to disease and infection. In spite of antibodies, setback may occur after recuperation within two to three weeks. Exceeding susceptibility to salmonella may be observed in sickle cell disease especially in osteomyelitis and more susceptible in AS haemoglobin than those that have AA haemoglobin (Geo et al. 2004, 257-258).


Salmonellae is one of the members of the family Enterobacteriaceae which has over two thousand serotypes characterized based on the variation in the flagella (H) and cell wall (O) antigens (Kauffmann-White scheme).

Apart from Salmonella typhi and Salmonella paratyphi, all salmonellae are found in animals, poultry and dairy products. Infection can occur through transmission from person to person especially, when a member of the family eats contaminated food or through faecal oral route (Cedric et al. 2004, 282-283). Enteric fever or Typhoid fever syndrome is produced by Salmonella typhi. The Salmonellae swallowed migrates to the small intestine through which they penetrate the lymphatics to the bloodstream (Geo et al 2004, 257) known as primary bacteraemia which is followed by reticuloendothelial system infection. The bacteria attacks the bloodstream and gut from the gall bladder again which then increases in Peyer's patches resulting in ulceration leading to complicated haemorrhage or damage (Stephen and Katheleen 2000, 40) . They are transported by the blood to different organs which includes the intestine, increases the intestinal lymphoid tissue and are expelled in stools (Geo et al 2004, 258). Symptoms occur after 10-14 days incubation period and they include: malaise, fever, constipation, myalgia, bradycardia, Fever is raised to a high plateau, liver and spleen becomes enlarged and rose spots are seen in rare cases on the skin and the chest. The mortality rate was 10-15% in the pre-antibiotic days which has reduced to less than 1%.

Inflammation of the gallbladder, lungs, periosteum and other organs, focal necrosis of the liver, hepatitis, necrosis of lymphoid tissue and hyperplasia are the principal lesions that occur in enteric fever (Geo et al. 2004 257-258).


Typhoid fever is described as the second common infection diagnosed in the laboratory and it is transferred through faecal-oral route from infected people to healthy individuals. Ingestion of shellfish from contaminated water and unhygienic behaviour of patients harbouring the organism can result to secondary infection. The inoculums' size that will make infection to occur is 100,000 bacteria. The mode of entry of these bacteria is usually by ingestion which has the significance of unknown aerosol transmission.

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About 2-5% of individuals that have been infected before, become chronic carriers that do not exhibit signs of disease but releases sufficient organisms that can infect others. Carriers harbour the bacteria in their gall bladder, biliary tract, intestine and sometimes, urinary tract. For instance, a food handler called "Typhoid" Mary Mallon, who was responsible for the transfer of the bacteria to about 78 people and killing 5 people. These carriers are highly infectious and have posed a serious risk to the society and public health due to their lack of symptoms of the disease (David 2003).

When treatment is started early, the damage done is limited and reversible. This leads to a reduced mortality rate among individuals that has been treated that possesses an antibiotic susceptible strain of Salmonella typhi which makes prognosis and patient's result a positive one.

The incidence of salmonella in chicken prepared in public has been published widely and the natural infection of cattle, rodents have made the bacteria to reside in tissues and eggs. The problem was made worse by the use of antimicrobial drugs contained in animal feeds which has supported the propagation of drug resistant salmonella that can be transmitted to humans.

The main sources of infection are contaminated drink and food such as milk and other dairy products, water, shellfish, meats and meat products, household pets, animal dyes used in drugs, cosmetics and foods, dried or frozen eggs and recreational drugs like Marijuana (Geo et al. 2004 257-258).


Salmonella typhi is a facultative anaerobic motile organism that is vulnerable to different antibiotics. About 107 strains of this organism have been detected to exhibit levels of virulence, metabolic characteristics and multidrug resistance genes that obscure treatment in regions that resistance is dominant (David 2003).


This species of Salmonella has some characteristics that make it to be pathogenic. It contain end toxin that characterizes it as a Gram negative organism, and Vi antigen which increase its virulence. Its ability to generate and excrete a protein called "invasion" enables non phagocytic cells to adopt the bacterium, where intracellular habitation occurs. It renders innate immune response useless by slowing down the oxidative disintegration of leukocytes (David 2003).

The life of plasmid-borne virulence genes was proposed in 1982, but recent studies showed that the role of plasmid in the pathogenesis of Salmonella is not so important but are heterogeneous in size and they share 7.8kb area which is needed multiplication in the reticuloendothelial system. The plasmid has different loci which include the conjugal transfer gene traT, fimbrial operon pef, and enigmatic rck and rsk loci. They function in other phases of infection process. Salmonella typhi has a virulence plasmid LT2 and it is self transmissible (Rafael et al. 1999)


Currently, there is no rapid, reliable and sensitive technique for detecting Salmonella typhi clinically. The clinical diagnosis of typhoid fever has been found to be insufficient in areas where enteric fever is rampant due to the non specificity of the symptoms caused and its relationship with other febrile diseases like dengue fever, malaria, melioidosis and leptospirosis transmitted in the environment (Liqing and Andrew 2010).

Serological tests such as the Widal test are used but have a low specificity and sensitivity and have no value practically in endemic regions in spite of their continued use (Levine et al 1978). The most effective diagnostic technique is the isolation of the causative agent in prognosed typhoid fever and the gold standard for the culture of Salmonella typhi is blood and has been in use for years. (Wain et al 2001).

Although, the sensitivity of blood culture rises to the peak during the first week of the disease and decreases when the disease advances (Kundu et al. 2001), blood culture consumes time and takes about 2-5 days for the isolation and identification of the organism to be complete. The amount of bacteraemia level of Salmonella typhi, blood sampled nature of blood culture used and the extent of incubation period will determine the percentage of patient samples that can be identified by blood culture. The normal percentage is 45-70 (Wain et al 2008)

There are different factors causing the failure of organism isolation from blood and they include intrinsic bactericidal activity of blood, insufficient laboratory media, and existence of antibiotics, period of blood and the volume of blood taken and used for culture. Another factor that affects isolation is the intracellular makeup of Salmonella typhi which reduces the speed of growth in blood culture media. Ox bile blood was preferred for culture in typhoid fever as recommended by Coleman and recognized the qualities attributed to the inhibition of bactericidal effect of blood and its capability to discharge intracellular bacteria. (Kaye et al. 1966).

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The diagnosis of enteric fever through serological techniques and blood culture has posed series of problem, therefore the use of polymerase chain reaction (PCR) methods were developed. Several studies were conducted in 1993 and it has been reported that PCR is a diagnostic tool for detecting the causative agent of typhoid fever when the flagellin of Salmonella typhi was magnified by Song et al in cases of confirmed typhoid fever and not from healthy controls (Ali et al. 2009). Great specificity and sensitivity were detected and reported in the studies when contrasted with blood culture proven positive samples and healthy controls. The amount of Salmonella bacteria moving in the blood of an individual with Salmonella bacteraemia is small. A study showed 0.5 to 22 bacteria per millilitre of blood in about 15 individuals with typhoid fever (Watson 1955) whereas another study showed a median of 0.3 bacteria per millilitre of blood from 81 individuals with typhoid fever (Wain 2001). Low ratio of bacteria to human deoxyribonucleic acid signifies that the PCR model in preparations is governed by DNA of mammals which can present a false positive indicator owing to the non specific connection of primers and the occurrence of false negative results because of decreased sensitivity. Excess of DNA lead to some problems for PCR in the detection of pathogen on blood especially in samples having low bacterial number (Handschur 2009). Small volumes of blood are adopted for the extraction of DNA or as a pattern in PCR which majorly lowers the sensitivity of the tests.


The development of chronic typhoid carrier state may be as a continuation of typhoid fever or after infection with the bacterium has occurred sub clinically. About 10% of the healthy population have been noticed to be chronic typhoid carriers according to Vi serology in endemic areas and subclinical typhoid infection has been forecasted to be very high than that of acute cases (Boyle et al. 2007, 1489-1495).

It has been reported that one third of gallbladder cancer occurrence shows significant titres of antibody against the Vi antigen of Salmonella typhi, but the level of the culture isolation of Salmonella typhi from gallbladder stone, bladder tissue and bile specimens from patients with gallbladder cancer has been detected to be very low with a percentage of about 10 (Butler et al. 1978, 407-410).

This low level of isolation has a link with either of the following:

Residence of the bacterium somewhere different from the gall bladder.

Presence of the bacterium in the biliary system in a feasible state but non culturable.

The bacteria may be present but few.

It could also be as a result of isolation technique inefficiency.

In other to conquer the above mentioned problems in the isolation of Salmonella typhi and to determine the likely niche of the bacterium, specific and sensitive nested PCR technique can be used on liver and gallbladder specimens.

In humans, Salmonella typhi can institute a severe infection after it has reached the gallbladder which persists after symptoms have subsided indicating the mechanisms that the bacterium uses for colonization in a bile rich surrounding (Vaishnavi et al. 2005 363-365).

Bile is a secretion produced in the liver functioning as a strong antimicrobial and emulsifying agent in the gastrointestinal tract. Despite its potency, salmonella has developed mechanisms for resisting the amphipatic properties acting like detergent on its surface (Van velkinburgh and Gunn 1999, 1614-1622). Bile also acts as a signal to the environment influencing virulence factor of intestinal pathogens such as salmonella species. (Gunn 2000, 907-913)

Chronic typhoid carriage is usually linked with gallbladder abnormalities, particularly gallstones but the sequence from infection to the carrier state cannot be defined (Lai et al. 1992, 1198-1199). The formation of gallstones can be linked to genetic and environmental causes associated with the supersaturation of cholesterol from bile which can be seen in patients for years without any form of symptom. (Maurer et al. 2009 425-440). Cholesterol is the major composition of gallbladder stones while bile duct stones are dominated by calcium bilirubinate (Hofmann 2005, 1126-1129)). Antibiotics administered clinically are not effective for disbanding the bacterial infection in carrier state of Salmonella typhi and cholesterol gallstones in gallbladder therefore, the rate at which the hepatobiliary carcinomas is developed is high (Kumar et al. 2006, 633-639). The most effective treatment for carriers of chronic typhoid with gallstones is the removal of the gallbladder (Robert et al. 2010)

Over the past two decades, industrial and medical settings associated bacteria biofilms have been known to be the cause of antibiotic resistant infections in man (Costerton et al. 1999, 1318-1322). The formation of biofilms occur in highly monitored sequential, stages which includes the development of self initiated, protective extracellular matrix, attachment of free swimming bacteria to a surface and liberation of plank tonic cells from sessile society into the surrounding (Costerton et al. 1995,711-745).

The observation suggested that the liver in chronic carriers is the major organ for the persistence of Salmonella typhi where excretion into the gallbladder occurs. Liver's involvement in acute typhoid fever can be envisaged when jaundice, hepatomegaly, raised bilirubin land serum enzyme levels occurs. Inability of cholecystectomy to eradicate the carrier state reveals that gallbladder is not the main niche of the bacterium in chronic typhoid carriers (Vogelsang 1964, 252). The mutagens released by the metabolic activity of the bacteria and the bacteria itself are concentrated as the gallbladder concentrates bile produced, thus, the main chemicals are generated by the gallbladder, leading to benign and malignant diseases of the gallbladder

Precautions must be taken to treat the chronic carrier state and to prevent the individual against cancer of the gallbladder and to aid in the eradication of typhoid fever globally. Investigations must also be carried out on immunohistochemistry and derangement of liver function test so as to determine the existence of Salmonella typhi in the liver (Gopal et al. 2010, 259-261).


Outer membrane protein (OMP) is a very important protein that extracts the immune response of the host because of their location (Ismail and Kader 1991, 301-305). It is only 50kDa protein that has experienced a multinational full scale clinical trial despite studies that have been done on series of antigenic candidates on OMP so as for easy evaluation of its diagnostic value (Karamat et al. 1997, 4). The 50kD OMP is specific and antigenic for Salmonella typhi because its reaction with typhoid sera is immunologic (Ismail et al.1991, 563-566). Further evaluation using the dot enzyme immunosorbent assay showed the ability of 50kD antigen to detect specific IgM and IgG presence in the sera of patients with acute typhoid (Choo et al. 1997, 96-99). Detection of specific IgG increases in endemic areas where the transmission of typhoid is high. The detection of specific IgG cannot be distinguished between recovery and acute cases hence, cases of false positive result can occur due to prior infection. When there if re-infection, secondary immune response followed by a major boosting effect of IgG above IgM occurs so that the latter will be hidden therefore, masking the consequence of IgM. One of the ways by which this problem can be solved is by unmasking the presence of IgM (Choo et al.1999, 175-183). The method that serves as the gold standard in the laboratory diagnosis of typhoid fever should be almost 100% in terms of specificity, sensitivity, positive and negative predictive values (Asma 2000, 3-8)

It is vital to know the antibody that would serve as an indicator for diagnosis of carriers during the development of serodiagnosis. Studies done with Vi antigen showed that the principal indicator for carriers is IgG while IgM plays no role. IgA can be seen in carrier and acute state. The sera of typhoid and dysentery carriers were found to contain secretory IgA and IgA when further test was conducted.

When the content of immunoglobulin in different kinds of typhoid fever is quantified, the carrier state reveals raised IgG and IgA which starts in the acute period. It has also been studied that there seems to be an elevation of about 2.4 times of IgA among carriers compared with non carriers that has a history of typhoid(Lashin et al. 1976, 75-78) whereas IgM is only raised in acute cases if typhoid and IgG is high amidst typhoid and typhoid carriers. Extended immunological stimulation is reflected in carriers with high content of IgA because IgA does not stay long in the body when it is formed. Detection of IgA amidst healthy individuals may also be an indication of typhoid carrier state. Vi antigen is widely spread and accepted as an indicator of the carrier state of typhoid. Different methods have been used in the advancement of diagnostic test that makes use of Vi antigen. One of the methods is passive heamaglutination assay which has been found to demonstrate high sensitivity and specificity particularly when is used in endemic regions. Before the method is used, the sera needs to be pre-absorbed with the red blood cell of sheep and this may not be easy for large population screening.

Another method is counterimmunoelectrophoresis which has been found to have high specificity and sensitivity when contrasted to heamaglutination test (Chau et al.1982, 261-267). ELISA format has also been tested but not successful due to poor binding of Vi antigen to microtiter plates unless it is tyraminated (Barett et al. 1983, 625-627). The use of tyramminated Vi antigen for ELISA test was highly recommended for the diagnosis of carriers with IgG serving as the indicator which is greater than or equal to 1:200 which is the cut-off titre (Asma 2000, 3-8).


Salmonella infections most of times needs no treatment and it resolves itself within five to seven days except if the patient is dehydrated or there is spread of infection from the intestines. Intravenous fluid is given to people with chronic diarrhoea. Antibiotic treatment is not always necessary but if infection persists or spreads to the intestine, antibiotics such as gentamicin, ampicillin, cefriaxone, amoxicillin, trimethoprim and ciprofloxacin can be given (Marlar, 2010)

Susceptibility testing is a vital option for the selection of appropriate antibiotic for multiple drug resistance occurrence transmitted by plasmids genetically amidst enteric fever.

Resistance of several drugs spread by plasmids genetically amidst enteric bacteria is a serious problem in infections with salmonella. Detection of Susceptible pathogen is an important adjunct in the selection of a good antibiotic. Since there is persistence of the organism in the gallbladder and biliary tract of carriers, it has been detected that ampicillin alone can cure the disease but in most cases, drug treatment is combined with cholecystectomy (Geo et al. 2004).

There is variation in the period of treatment depending on the duration of illness and the range is 6 weeks for bacteraemia and 4 days for enteric fever (Malar, 2010).

Measures should be taken in other to check the contamination of water and food by animals that shed salmonella. Meats, eggs and poultry that are infected must be cooked properly. Hygienic precautions must be observed by food handlers that are carriers or they should not be allowed to handle food.

Partial resistance to small typhoid bacilli and not large ones is given when two injections of acetone killed suspension of bacteria containing Salmonella typhi along with booster injection is administered. In regions of elevated endemicity, live avirulent mutant strain of Salmonella typhi administered orally has offered protection. Vaccines that are not for other salmonella are not recommended and do not give good result (Geo et al. 2004)


One Sample T-Test for the age

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Chi-Square Test analysis for the Vi antibody titres


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One Sample T-Test analysis of the Vi antibody titre

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The genus Salmonella consists of organisms that are gram negative rods, anaerobic, facultative and motile. They are among the family of the Enterobacteriaceae responsible for causing enteric fever, septicaemia etc in individuals of different places and locations. Man, animals and birds serve as hosts to Salmonellae and are classified into 1800 serotypes and biotypes based on the Kauffmann white classification. The classification of this species is based on the somatic (O), flagella (H) and Vi antigen using the slide agglutination technique with known antisera. Salmonella typhi possesses the Vi antigen which covers the outer layer of the cell wall. It masks the O antigen when fully developed and it is agglutinable with the specific antisera. These species of Salmonella are catalase positive, oxidase negative, usually H2S positive and citrate positive.

Over the years, Salmonella typhi and paratyphi, both members of the same family have been known to cause enteric fever or typhoid fever as a result of infection mainly through oral route and known to infect the gall bladder, kidneys and the reticuloendothelial system. The rate of infection of the organism is dependent upon the susceptibility and reoccurrence of that causative agent

It has been reported that one third of gallbladder cancer occurrence shows significant titres of antibody against the Vi antigen of Salmonella typhi, but the level of the culture isolation of Salmonella typhi from gallbladder stone, bladder tissue and bile specimens from patients with gallbladder cancer has been detected to be very low with a percentage of about10 (4).

Results gotten form the widal test can only be termed significant when the Vi antibody titer is above 1:100 and in this case 1:160 since it is a doubling dilution test. A given population at a given time determines the baseline titer values as two locations can hardly have the same baseline owing to the differences in infection control.

Based on the result gotten for the test, the mean and standard deviation of the ages where computed according to sex with that of the males as 48.47 ± 13.7 and that of the females as 48.20 ± 12.6 and was found to be significant at P = 0.00 using the One Sample T-Test with a confidence interval of 95%. This is because more males than females were enrolled. Out of the 102 subjects that were enrolled for the research, three (3) had Salmonella typhi as growth in culture with a titer of <1:40 which is not significant compared to the population size enrolled. This goes to tell us that salmonella is not the only organism harvested from bile as E. Coli, Klebsiella and pseudomonas were also harvested and the prevalence of Salmonella typhi or paratyphi is not significant. It is more accurate and reliable to run the test in the first week of infection and in the third week as this gives room for a twofold rise in titre.

Also, the Vi antigen titres gotten from the test does not depict significance for those who had the vaccination before and even those that had typhoid fever before are supposed to have a high titre but still had a titre that is not up to 1:100. This therefore indicates that Malaysia is not an endemic region.

It is suggested that more research should be carried out to know the prevalence of Salmonella typhi and paratyphi in the population.


The anti-Vi test is still used for the lack of a better test for carrier diagnosis. The ideal carrier detection test should be easily used and interpreted in the field rather than in the laboratory to allow for immediate diagnosis. The development of a test using the immunochromatography or dipstick method may be more useful for convenient carrier detection in the field. Development of multi-test for simultaneous typhoid and typhoid carrier diagnosis will be able to have a greater impact on the control and management of typhoid fever. Multi-tests developed for the detection of the organism in environmental samples would also enhance typhoid control since it would allow for tracing of the source of contamination. While carrier detection is important for public health, reports have also shown a close relationship between biliary disease and chronic carriers (51). Recent developments have shown that the risk of gallbladder carcinoma has increased among typhoid carriers (52, 53, and 54). Hence a test to detect for typhoid carriers that is cheap, sensitive, specific and user friendly for field work would promote not only effective management but also reduce gallbladder carcinoma and dysfunction- ASMA ISMAIL.