Sources of Meningococcal Infection - Essay Example

 Sources of meningococcal infection This coursework is based broadly on the case study below, and then includes further questions based on microbial causes of meningitis. Throughout, your answers must be based on cited evidence/literature. Where required, answers will need to contain microbiological details of infectious disease, including microbiological, cellular and molecular details of interactions between bacteria and host. Where appropriate, answer lengths are based on single line spaced Times New Roman 12pt font, e.g. [½ page]. Please use this fontsize. Answers should be concise and precise, containing sufficient detail to ensure clarity. Remember that this item is the coursework for this module (50% of the module mark. See Module Guide for information. As a guide this assessment should required 24h-48h of student effort). Where required answers must be presented in the format given (e.g. tabular, with all workings etc as stipulated). Literature in addition to the module textbook will need to be consulted. Referencing: details of all reference sources must be correctly presented throughout the answer texts and at the end – and remember that you must not plagiarise. Do not copy word-for-word or quote from sources, but write using your own words. Case study A 19-year old student was well, until the evening before admission to the A&E department, when he went to bed with a headache. He told one of his flat mates that he felt feverish, and the following morning he was found in bed, moaning and lethargic. He was taken to hospital where he appeared drowsy but orientated,with a temperature of 40°C and a heart rate of 126/min. His neck was supple and he had an impressive, non-blanching purpuric rash prominently on his trunk, wrists and legs. Meningococcal septicaemia due to Neisseria meningitidis was suspected, confirmed by blood cultures showing Gram-negative diplococci. A lumbar puncture was considered. Antibiotic therapy was started before the results from the lab were available and he recovered well. Questions: 1. What are the likely sources of meningococcal infection? 2 marks [Few sentences] Neisseria meningitidis colonizes the nasopharyngeal mucosa of as much as 10 percent of the population, mostly young adults. These individuals act as asymptomatic carriers and have the bacteria present in nasopharyngeal secretions. Pathogenic strains can cause invasive infection in the individual after colonization and invading the mucosa to access the bloodstream. The bacteria are transferred from asymptomatic carriers to non-immune persons through droplets of nasopharyngeal secretions or by direct contact (kissing) (Brandtzaeg and van Deuren, 2012). 2. Neisseria meningitidis is the most common cause of meningitis.Using HPA (Health Protection Agency) data plot your own graph comparing UK serotype data over the 10 years up to 2009/10. Comment on these data. 4 marks [2/3rd page, including graph] Health Protection Agency, 2011. The plot shows an overall declining trend in the incidence of meningitis by its three most common serotypes between 2001-2010. Serotype B was responsible for the majority of cases, with annual incidences in the thousands range, while serotypes C and W135 had less than 400 cases per year. This pattern can be explained by the widespread immunisation available against N. meningitides, but the vaccine does not protect against the B serotype. An outbreak of serotype B meningitis occurred in 2005 with a surge in the number of cases. The remaining serotypes – Y, and others that were not typed (and cannot be depicted in above graph due to small number), had a total incidence of about or less than 100/year. 3. Briefly consider a more world-wide perspective of meningococcal disease. 2 marks [½ page] An estimated 500,000 cases of meningococcal disease occur globally each year, with a mortality rate of about 10%. The predominant serotype varies by region, with serogroup A causing outbreaks in sub-Saharan Africa, and it has caused outbreaks in New Zealand, China, Nepal, Mongolia, India, Pakistan, Poland, and Russia.Serogroup B causes more prolonged outbreaks. Most incidences today are sporadic at a rate of about 0.3–5 cases per 100,000 population, rather than outbreaks or epidemics. 4. Discuss the current understanding ofN.meningitidispathogenesis and the range of virulence factors, then use this knowledge to explain thesymptoms of meningococcal meningitis. 5 marks [1 page] N.meningitidisis a gram-negative aerobic diplococcus that causes infection and colonization in humans only. It has many different pathogenic and non-pathogenic strains circulating among asymptomatic carriers. He pathogeic strains are always encapsulated. Many carriers are immune and carry a pathogenic strain that, if transferred to a non-immune person, causes invasive disease in the latter. Some strains stay as colonizers for a time before invading the mucosa and causing infection. After invading the mucosa, the bacteria enter the bloodstream and seed various body organs, such as the meninges and joints. Its virulence factors include its surface capsule that protects against dessication in the atmosphere and phagocytosis in the body. Its surface adhesins, including Opa proteins and pili, interact with ligands on nasopharyngeal mucosal epithelial cells to attach effectively to the nasopharyngeal epithelium. It secretes IgA protease, which protects it from the antibacterial effect of IgA on the epithelial surface. The diversity in its surface antigens prevents the development of powerful host B and T cell immunity. As the meningococci replicate in the bloodstream, the bacterial cells release endotoxin, which activates inflammatory cells through CD14 to stimulate an inflammatory cascade. The inflammatory mediators including interleukins, prostaglandins and TNF-a, mediate the symptoms of disease – fever, weakness, pain. Endothelial injury occurs in the process, leading to increased capillary permeability, which leads to hypovolemia, pulmonary edema, and renal failure. Intravascular thromboses can occur, leading to tissue infarcts and depleting platelets. The characteristic skin rash is due to bleeding caused by the relative deficiency of platelets, as well as vasculitis. The hypovolemia can culmiane in shock. Bacteria that reach the meninges cause a local inflammatory response in the area, causing clinical meningitis. Endothelial injury in the area can cause rerebral edema and raised intracranial pressure (Pollard, 2012). 5. Briefly discuss long term clinical consequences of meningitis. 3 marks [½ page] The complications of meningitis include: 1. Scarring of skin lesions, leading to permanent disfiguration 2. Limb ischemia, which can progress to gangrene, necessitating amputation of the affected limb. It occurs in about 2 percent of survivors. 3. Acute renal failure. This is usually reversible, but may be irreversible in some cases. 4. Permanent neurological damage. This may be in the form of hearing loss, blindness, focal paralysis, strabismus, cognitive deficits, and psychiatric disorders such as schizophrenia and attention deficit/hyperactivity disorder (Pollard, 2012). 6. Describe the routine laboratory techniques and tests (microscopy, bacterial culture media and conditions, biochemical tests and serology) used to isolate and identify N.meningitidis. 4 marks [⅓ page] These techniques include: 1. Blood Gram stain and culture. Culture on blood or chocolate agar, incubated at 37°C in an atmosphere of 5% CO2, shows positive growth of the organism in about 75% of cases of meningitis. The culture medium must not contain sodium polyanetholsulfonate, which can inhibit meningococcal growth. 2. Culture of nasopharyngeal swab, using modified Thayer-Martin medium with antibiotics (vancomycin, colistin, amphotericin). This mediumfavors the growth of neisseriae while inhibiting other nasopharyngeal flora. 3. RT-PCR of blood or CSF sample for meningococcal DNA, which can pick many cases missed by other methods. 4. Cerebrospinal fluid (CSF) gram stain and culture, by obtaining a sample by lumbar puncture. The gram stain has a sensitivity of up to 80% for meningococcus, and shows the bean-shaped, Gram-negative diplococci. The culture will show growth of the organism in meningitis. 5. Latex particle agglutination test for meningococcal antigens of CSF sample or urine. This test less sensitive but provides rapid results, and is useful if laboratory facilities are not available. Source: Brooks, 2010. 7. Discuss some examples of types of ELISAs used in meningococcal research/typing/identification, including whether they are direct or indirect ELISAs. 2 marks [½ page] Direct ELISA uses antibodies to detect the presence of the infectious agent’s antigens. Indirect ELISA uses antigens to detect presence of antibodies to the organism’s antigens. Current ELISAs available use antigens of serogroups A, C, Y and W-135 to detect IgG antibodies to Neisseria meningitis, and are thus indirect assays. Quantitative titre assays are available. Most assays use a combination of antigens, although multiplex conjugated polysaccharides have been developes, where all the antigens are attached in a single molecule. Whole-cell ELISAs have also been used in research, where whole bacterial cells rather than polysaccharide molecule antigens are used. 8. If problems were encountered attempting to identify N.meningitidisin a human isolate and therefore there was a needto consult the UK experts, which reference unit would you contact and where is it located? 1 mark. [1-2 sentences] The Meningococcal Reference Unit must be notified. The unit, located at theManchester Royal Infirmary, works under the HPA to optimise meningococcal disease diagnosis through surveillance. Telephone #: 44(0)161 276 6757 Fax #: 44(0)161 276 5744 Out-of-hours Telephone #: 44(0)161 276 1234, and ask for Medical Microbiologist on-call. Postal address: Meningococcal Reference Unit Manchester Medical Microbiology Partnership PO Box 209 Clinical Sciences Building 2 Manchester Royal Infirmary, Oxford Road Manchester, UK M13 9WZ For identification, phenotypic characterisation (serogroup, serotyping, subtyping), molecular characterisation (porA sequencing) and susceptibility testing of isolates, antigen detection, PCR, and requests for molecular epidemiology, the following persons can be contacted: Tel: 0161 276 6757 Dr Stephen J Gray BMS3 Tel: #44(0)161 276 6757 steve.gray@hpa.org.uk Mr Anthony Carr, BMS2 tony.carr@hpa.org.uk Mrs Lynne Newbold, BMS2 lynne.newbold@hpa.org.uk Source: HPA, 2012 9. Using research literature, discuss some developments and applications of molecular analysis in the identification of N.meningitidis. 5 marks [½-1 page] Molecular diagnostic techniques are used to investigate outbreaks and the spread of N. Meningitides, and to determine the genetic structure of pathogenic strains. They provide several advantages over bacterial culture, such as faster results, detection of specific strains and clones to study outbreak patterns, and detection of an organism in very low levels in the body that could be missed by culture. The specific technique used depends on the epidemiological question. Real-time polymerase chain reaction (RT-PCR) can be used to confirm the presence of N.meningitidis infection. It has a high sensitivity and specificity for diagnosis, especially the fluorescence-based format. It can predict the type, group and subtype of meningococci. Multi-locus sequence typing with PCR allows detection of specific clones and pathogenic or drug-resistance genes. (Diggle et al., 2006). For more localised outbreaks, other techniques can be used to investigate less clonal serogroup B and C meningococci. These include PCR-ribotyping, multilocus enzyme electrophoresis (MLEE), pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST). These tests can determine the relationship between different pathogenic strains. MLEE and MLST are quantitative methods that can assess the relationship between newly isolated strains and endemic strains. 10. What antibiotic treatment may have been given to the patient in the case study?Is antibiotic resistance a problem in N.meningitidis, particularly in the UK? 3 marks [⅓ page] The patient can be given an intravenous third-generation cephalosporin such as ceftriaxone, 75–100 mg/kg per day (maximum, 4 g/d) in one or two divided doses, for a total of 7 days (Pollard, 2012). Ceftriaxone covers other bacteria as well, that would be resistant to penicillin, such as S. pneumonia, which is often resistant to penicillin, and H. influenza. Meningococcus resistance to penicillin has been reported, but resistance to ceftriaxone is not yet a significant concern, and it is still included in national guidelines (NICE, 2010). 11. Makers of a quaternary ammonium chloride based disinfectants, typically used in schools and other institutions claim that these disinfectants will be effective against the pathogens that cause bacterial meningitis and for use on eating utensils, soda cans, water bottles or drinking glasses. To investigate the effectiveness of the disinfectant, a laboratory assessed the effect of the disinfectant solution on the viability of a non-pathogenic Neisseria species by incubating bacteria in different concentrations of the disinfectant at room temperature and performing viable counts by plating out suspensions onto an agar medium. Viable count results are given in Table 1 below: Table 1. The effect of disinfectant concentration on Neisseria a) Process the data, plot an appropriate graph and calculate the Decimal Reduction Times (D-values) for the three concentrations of disinfectant against the Neisseria.[You will need to find out how to plot data in order to calculate Decimal Reduction Times].You must show ALL your workings clearly and logically, including how D-values were determined, ON THE GRAPH. Graphs may be hand-drawn or computer generated but they must be of sufficient size, data points must be shown and AND lines showing how the D-values were determined clearly shown. 6 marks Log 10 values: 25% 10% 5% 0 8.51 8.51 8.51 2 7.00 7.80 8.30 20 4.34 6.90 8.11 40   5.34 7.60 60   3.51 5.45 80     4.75 t = D × (log No-log Nf) = D × n, where D = D-value (min) at specified conditions, No = bioburden of the chosen bacterium as the BI; Nf = surviving population after an exposure time, t (min), to the selected disinfectant n = (log No-log Nf) = log10 reduction of a bioburden. D-value of 25% solution: 20= D x (8.51-4.34) D= 20 ÷ (8.51-4.34) = 4.8 mins D-value of 10% solution: 20= D x (8.51-6.9) D = 20 ÷ (8.51-6.9) = 12.6 mins D-value of 5% solution: 20= D X (8.51-8.11). D= 20 ÷ (8.51-8.11) = 50 mins b) Disinfectant activity is more realistically assessed with “in-use” tests. Was this the case with the test used? Explain your reasoning. 2 marks [1 paragraph answer] In-use tests involve determining whether a disinfectant is destroying the bacteria immersed in it. The test involves immersing a contaminated object into the disinfectant solution to introduce bacteria into it, allowing time for disinfectant to act, and then inactivating the disinfectant in the solution, by adding a solution such as lecithin. The solution sample is then tested for live bacteria by culture on agar plates. In the above experiment, the disinfectant was not inactivated, and its effectiveness at various time intervals in the agar plates was measured. Thus, it was not a true ‘in-use test’. 12. Meningitis can be caused by a variety of different bacteria other than N.meningitidis, and also by some fungi and protozoa.  Using the table format below, list 4 bacteria, 2 fungi and 1 protozoan amoeba, with one sentenceabout susceptible hosts for each one. 4 marks [½ page] Microbe Species name Information about hosts (1 sentence) Bacteria 1 Streptococcus pneumonia It is the most common cause of meningitis in adults more than 20 years old. 2Hemophilusinfluenzae Patients with otitis media, mastoiditis or sinusitis can get meningitis with H.influenzae by contiguous spread. 3 Listeria monocytogenes It is an important cause of meningitis in neonates, pregnant women, individuals older than 60 years, and immunocompromisedpatients. 4 Streptococcus agalactiae It is often present in the female genital tract lining, and thus is an important cause of neonates born by vaginal delivery. Fungi 1Cryptococcus neoformans Meningitis with Cryptococcus is rare in the absence of impaired immunity, it usually occurs in patients with HIV/AIDS or some other immunodeficiency state. 2 Candida albicans It also infects immunocompromised individuals Protozoan 1 Malaria Patients with cerebral malaria present with altered mental status, seizures, and meningismus, and must be treated with intravenous antimalarials in an intensive care or special care unit. Source: Longo et al. (2012) 13. Vaccination is used for protection against meningococcal infection. How effective is this? Briefly discuss vaccines currently in use and any reasons for lack of comprehensive vaccines for all meningococcal meningitis strains/serotypes. 2 marks(½ page) Capsular polysaccharide vaccines for N.meningitidis are available, formulated as bivalent serogroups(A and C) or quadrivalent (serogroups A, C, Y, and W135). The vaccine has an immunity efficacy lasting only 3-5 years, and booster doses do not increase the immune response as only B cells but T cells are not stimulated by it and memory cells are not made. Conjugate vaccines, bound to a carrier protein, for serotypes A, C, Y, and W135 have been developed, which are more effective, and produce enhanced immunity on booster doses by T cell stimulation. It is recommended for all children and adults. There is no vaccine available for serogroup B. This is because a protein expressed by fetal neural cells is similar to the B antigen of N.meningitidis serotype B. thus, the antigen is recognized as ‘self’ and is not immunogenic in humans (Pollard, 2012). 14. For bacterial meningitis, it is also important to know which type of bacteria is causing the meningitis because antibiotics can prevent some types from spreading and infecting other people. Briefly discuss chemoprophylaxis for contacts of meningococcal disease, specifying antimicrobials which have proved effective. 2 marks [1 short paragraph] Close contacts and healthcare providers exposed to meningococcus patients are offered prophylaxis with medications to prevent development of invasive disease in case they have been colonized by the pathogen. Chemoprophylaxis eradicates colonization with the pathogen, and should be given to exposed individuals as soon as possible. Possible regimens include: 1. Rifampin, 600 mg orally twice daily for 2 days 2. Ceftriaxone, 1000 mg single injection 3. Ciprofloxacin, 500 mg as a single dose 15. Many different viruses can cause viral meningitis, and most people are exposed to some of them during their life without developing meningitis. Using the table format below, name 4of the most significant viruses and give some informationabout their epidemiology and diseases (20 words maximum). Expand the table as required. 4 marks [1 page] Virus name Epidemiology (20 words max) Comments on disease/pathology (20 words max) Coxsackievirus One of most common causes – the etiology in 40% of aseptic meningitis cases. More common in autumn and winter. Enters bloodstream through nasal or gastrointestinal tract, viremia precedes meningitis. Meningitis may be mild or subclinical, or severe with encephalitis Herpes simplex virus type 2 HSV-2 is more common in STD patients. Aseptic meningitis occurs in about 15% of HSV-2 patients. HSV-2 is an STD, causing genital ulcers. Primary HSV-2 infection in women often presents as aseptic meningitis. It can cause recurrent meningitis and a mild, non nonspecific neurologic syndrome. Human enterovirus 68-71 More than half infections are subclinical. More common in crowded areas, infants and young children. Replicate in gastrointestinal tract, invade bloodstream to reach CNS Human immunodeficiency virus Uncommon, but must be suspected in any patient with acute CNS symptoms Aseptic meningitis can occur in the early stages with acute HIV syndrome, with headache, photophobia and meningismus. 16. How may the cause/s of viral meningitis be identified? (Include at least 3 different types of clinical microbiology or biochemistry laboratory tests). 3 marks [½ page] Acute viral meningitis can be diagnosed using a variety of laboratory techniques. These include: 1. PCR of cerebrospinal fluid for viral DNA or RNA. This is a highly sensitive and specific technique for detection and identification of the viral etiology. 2. Viral cultures. These are time-consuming and not commonly done. 3. Viral serology. In many cases, antibodies to the virus are present in the bloodstream and can be detected by serology. References.Remember to use academically credible information sources. Reference your work throughout the text and list fully and correctly ALL the references you used to complete this work. They must be presented in the Harvard format.Present them alphabetically and do not divide them into different types (e.g. books, journal articles etc). 4 marks ------- END -------- References Brandtzaeg, P., van Deuren, M. 2012. Classification and pathogenesis of meningococcal infections.Methods of Molecular Biology, 799, pp. 21-35. Brooks G.F., Carroll K.C., Butel J.S., Morse S.A., Mietzneron T.A. 2010. The Neisseriae.In G.F. Brooks, K.C. Carroll, J.S. Butel, S.A. Morse, T.A. Mietzneron, eds. 2010.Jawetz, Melnick, &Adelberg's Medical Microbiology. 25e. New York: McGraw-Hill, Inc. Chapter 20. Diggle, M.A., Clarke, S.C.2006.Molecular methods for the detection and characterization of Neisseria meningitidis. Expert Review of Molecular Diagnostics, 6(1):79-87. Faculty of Biological Sciences, University of Leeds, (2008). Microbiology Teaching Support. Killing (and maiming) bacteria. The 'in-use' test. [online]. Available at: http://www.bmb.leeds.ac.uk/mbiology/ug/ugteach/micr1010/videos/MICR1010_Practical_04_Kiling_and_Maiming/In_use_test.html. [Accessed March 10, 2012]. Health Protection Agency, 2011. Meningococcal Reference Unit: Isolates of Neisseria menengitidis; England and Wales, by serogroup & calendar year, 1998-2010. [online]. Available at: http://www.hpa.org.uk/web/HPAweb&HPAwebStandard/HPAweb_C/1234859712887. [Accessed March 10, 2012]. National Institute for Health and Clinical Excellence, 2010.Bacterial meningitis and meningococcal septicaemia: Management of bacterial meningitis and meningococcal septicaemia in children and young people younger than 16 years in primary and secondary care. [online]. Available at: http://www.nice.org.uk/nicemedia/live/13027/49339/49339.pdf [Accessed March 7, 2012] Martins, T.B., Jaskowski, T.D., Tebo, A., Hill, H.R. (2009). Development of a multiplexed fluorescent immunoassay for the quantitation of antibody responses to four Neisseria meningitidis serogroups. Journal of Immunological Methods, 342(1-2):98-105. Mazzola, P.G., Penna, T.C., Martins, A.M. (2003). Determination of decimal reduction time (D value) of chemical agents used in hospitals for disinfection purposes. Bio Med Central Infectious Diseases. 17;3:24. Pollard A.J. (2012). Meningococcal Infections. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo, eds.2012. Harrison's Principles of Internal Medicine. 18e. New York: McGraw-Hill, Inc. Chapter 143. Yakubu, D.E., Abadi, F.J.R., Pennington, T.H. (1999). Molecular typing methods for Neisseria meningitides. Journal of Medical Microbiology, 48:1055-1064. Read More