COMMON INFECTIOUS DISEASES AND THEIR SEROLOGY.pptx

Infectious diseases serology

1. COMMON INFECTIOUS DISEASES By: sekyanzi pascal

2. SYPHILIS The laboratory diagnosis of syphilis depends on demonstration of microorganisms in a lesion and serologic testing. Serologic methods measure the presence of two types of antibodies, through nontreponemal methods and treponemal methods. Traditional serologic screening initially uses nontreponemal testing with confirmation of positive results using a treponemal assay. New “reverse algorithms” is to use treponemal testing initially with confirmation of reactive results using a nontreponemal assay.

3. Nontreponemal Methods Nontreponemal methods determine the presence of reagin , an antibody formed against cardiolipin . An antigen composed of cardiolipin , a lipid remnant of damaged cells, cholesterol, and lecithin, is used to detect the nontreponemal reagin antibodies.

4. Rapid Plasma Reagin RPR test is the most widely used nontreponemal procedure , although VDRL may be used in some clinical and reference laboratories. Both are flocculation or agglutination tests in which soluble antigen particles forms larger particles that are visible as clumps when they are aggregated by antibody . The RPR test, a charcoal agglutination test, can be performed on heated or unheated serum or plasma. The RPR card test antigen also contains charcoal particles to which cardiolipin -containing antigen is bound for macroscopic reading.

5. If antibodies are present, they combine with the lipid particles of the antigen, causing them to agglutinate. The charcoal particles coagglutinate with the antibodies and show up as black clumps against the white card. If antibodies are not present, the test mixture is uniformly gray . False-positive results may occur in HSV, HIV, intravenous drug use, leprosy, malaria, pregnancy, RA, and SLE.

6. Treponemal Methods Treponemal assays detect specific IgG and/or IgM directed against T. pallidum . • Chemiluminescence immunoassays (CIAs/EIAs) • Enzyme-linked immunosorbent assays (ELISAs) • T. pallidum antibody by microbead immunoassays (MBIAs) • T. pallidum particle agglutination (TP-PA) • Fluorescent treponemal antibody absorption (FTA-ABS)

7. TOXOPLASMOSIS Diagnosis is by mostly serology. IgG is used to determine whether a person has been infected. IgM is used to estimate the time of infection, particular for pregnant women. The diagnosis of toxoplasmosis can be established by the following: • Serologic tests • Polymerase chain reaction (PCR) • Indirect fluorescent antibody (IFA) • Isolation of the organism • Histology examination of infected tissue (IHC); provides a definitive diagnosis.

8. RUBELLA The rubella virus is a single-stranded, enveloped RNA virus of the genus Rubivirus , family Togaviridae . It is transmitted through respiratory droplets or through transplacental infection of the fetus during pregnancy. It is the cause of the benign , self-limited disease also known as German measles . I ncubation period: varies from 10 to 21 days (average 12 to 14 days). Infected persons are contagious for 12 to 15 days, beginning 5 to 7 days before the appearance of a rash. Following an incubation period, the virus replicates in the upper respiratory tract and cervical lymph nodes, then travels to the bloodstream.

9. Immunologic Manifestations In acquired rubella, IgM antibodies become detectable a few days after the onset of signs and symptoms and reach peak levels at 7 to 10 days. They persist but rapidly diminish over the next 4 to 5 weeks, until no longer detectable . IgM antibody in a single specimen suggests that the patient has recently experienced a rubella. IgG increase rapidly for the next 7 to 21 days and then level off or even decrease in strength. IgG, however, remain present and protective indefinitely. Detection of IgG is a useful indicator of rubella only when blood specimens are drawn 2 or more weeks apart. If both IgM and IgG are negative, the patient has never had rubella or been vaccinated. Such patients are susceptible to infection. If no IgM is demonstrable but IgG is present in paired specimens, the patient is immune.

10. In congenital, because IgG antibody is capable of crossing the placental barrier, there is no way of distinguishing between fetal IgG and IgG of maternal origin in a neonatal blood specimen. Testing for IgM antibody is very helpful for the diagnosis of congenital rubella syndrome in the neonate. IgM does not cross an intact placental barrier; therefore, demonstration of IgM in a single neonatal specimen is diagnostic of congenital rubella syndrome.

11. RUBEOLA (MEASLES ) Rubeola is referred to as measles. Measles is a highly contagious disease caused by the rubeola virus, a single-stranded RNA virus, the only member of the genus Morbillivirus ( Paramyxoviridae family ). Laboratory confirmation is made by the detection of measles-specific IgM antibodies in serum, isolation of measles virus, or detection of measles virus RNA by nucleic acid amplification in an appropriate clinical specimen (e.g., nasopharyngeal or oropharyngeal swabs, nasal aspirates, throat washes, or urine).

12. MUMPS The mumps virus is a single-stranded RNA virus that belongs to the Paramyxoviridae family (genus Rubulavirus ). It is transmitted by infected respiratory droplets, and replicates initially in the nasopharynx and regional lymph nodes. I ncubation period:14 to 18 days. The virus spreads from the blood to various tissues, including the meninges of the brain, salivary glands, pancreas, testes, and ovaries, producing inflammation at those sites . The diagnosis of mumps is usually made on the basis of clinical symptoms, especially parotitis , and does not require laboratory confirmation. Some methods detect mumps antibodies, including complement fixation, hemagglutination inhibition, hemolysis in gel, neutralization assays, immunofluorescence assay, and ELISA.

13. Current or recent infection: presence of mumps-specific IgM in a single serum sample or by at least a fourfold rise in specific IgG antibody between two specimens collected during the acute and convalescent phases of illness. IgM can be detected within 3 to 4 days of illness and can persist for at least 8 to 12 weeks. IgG become detectable within 7 to 10 days and persist for years. The presence of specific IgG antibodies indicates immunity to mumps . A vaccine consisting of live, attenuated rubella virus was developed with the primary goal of preventing infection of pregnant women. The vaccine is usually given in combination with vaccines for measles and mumps (measles/mumps/rubella [MMR] vaccine) and possibly with varicella (MMRV ).

14. ACQUIRED IMMUNODEFICIENCY SYNDROME (AIDS) Patients with AIDS exhibit some of the most severe manifestations of cell-mediated immunity . Human immunodeficiency virus (HIV) is the predominant virus responsible for AIDS . HIV is a member of the family Retroviridae . Two distinct HIV viruses, types 1 and 2 (HIV-1 and HIV-2), cause AIDS . HIV-1 is divided into nine subtypes: group M (subtypes A–H), group N, and group O. HIV-2 is divided into two subtypes: groups A and B. The HIV-1 virus is composed of a lipid membrane, structural proteins, and glycoproteins that protrude. The viral genome consists of three important structural components—pol, gag, and env .

15. Retroviruses contain a + ss RNA and enzyme called reverse transcriptase in their core. Reverse transcriptase enables the virus to convert viral RNA into DNA. This reverses the normal process of transcription in which DNA is converted to RNA—thus the term retrovirus. In the provirus, which is formed when cDNA synthesis is completed from the RNA template; viral core protein, envelope protein, and reverse transcriptase are encoded by the gag, env , and pol genes, respectively, whereas viral gene expression is regulated by tat, trs , sor , and 3′orf gene products .

16. Modes of Transmission Heterosexual contact. HIV-2 is less harmful (cytopathic) to the cells of the immune system and it reproduces slowly. HIV has been isolated from blood, semen, vaginal secretions, saliva, tears, breast milk, CSF, amniotic fluid, and urine. Only blood, semen, vaginal secretions, and breast milk have been implicated in the transmission of HIV to date. Also found in saliva and tears in very low quantities from some AIDS patients. Not from the sweat.

17. Diagnosis T-lymphocyte counts (lowered). CD4+ lymphocytes (lowered). CD4+/CD8+ ratio (Normal person “2:1”, AIDS “0.5:1”). Serological markers (detection of core Ag, Abs against HIV). ELISAs. PCR HIV Viral load Western blotting Other tests (CBC, LFTs, RFTs, for opportunistic infections).

18. Serologic Markers T he first signal of an immune response to HIV-1 infection is the appearance of acute-phase reactants, including α1-antitrypsin and serum amyloid in plasma 3 to 5 days after transmission. F ollowed by a steep rise in the HIV-1 viral load (ramp-up viremia) that coincides with a large burst of inflammatory cytokines led by interferon-α and IL-15 and by a burst of plasma microparticles derived from infected CD4 T cells undergoing apoptosis. Increased production of core antigen is believed to be associated with a burst of viral replication and host cell lysis. A sudden decrease in anti-p24 is considered to be a grave prognostic sign in HIV-1–infected patients.

19. Antibodies Some antibodies neutralize the virus, others prevent it from binding to cells, and others stimulate cytotoxic cells to attack HIV-infected cells. A window period of seronegativity exists from the time of initial infection to 6 or 12 weeks or longer thereafter. Anti-gp41 are detectable for weeks or months before anti-p24. The gp41 antibodies persist throughout the course of infection. Antibodies specific for p24 not only rise to detectable levels after gp41 but also can disappear unpredictably and abruptly. The disappearance of anti-p24 occurs concomitantly with an increase in the concentration of core antigen in the serum due to the sequestration of antibody in immune complexes.

20. THANK YOU FOR ATTENDING. WISHING YOU ALL THE BEST IN THE NEXT CORE: MICROBIOLOGY