Quiz 2

Ref: Harrison 20th edition pg. 1597; Katzung 13th edition pg, 901
RK 39 dipstick test is a rapid immunochromatographic test being widely used in diagnosis of Visceral Leishmaniasis. The test requires a drop of finger prick blood and the result can be read in 15 minutes. Liposomal amphotericin B is the drug of choice for management of Leishmaniasis.

Ref: Manson's Tropical diseases 23rd edition, page 491
• Urinary Lipoarabinomannan allows for detection of MTB, including extra-pulmonary or disseminated forms of disease. The WHO has recently advocated the use of lateral flow LAM assay for HIV infected hospitalized individuals with CD4 < 100.
• Lipoarabinomannan is involved in pathogen host interaction and facilitates the survival of M. Tuberculosis.
• This test is in addition to XPERT MTB/ RIF, a rapid nucleic acid amplification test for extra-pulmonary TB diagnosis.

Ref: Harrison 20th edition, p 1487; Manson's Tropical diseases: 23rd edition, page 201
• The ante-mortem test for diagnosis of rabies is direct fluorescent antibody on skin sample taken from hairy area like the nape of the neck. Hence choice A is ruled out.
• Real time PCR is not routinely available and is done on saliva, CSF and skin biopsy and not corneal impression smears. Hence choice B is ruled out.
• Stain for Negri Bodies is done for brain tissue where the negri bodies are found in the hippocampus (Ammon horn), cerebellar purkinje fibres and cortical neurons. Hence choice D is ruled out.
• Culture of virus is most successful in the first week of illness. Viral culture is done on brain tissue, saliva, tracheal, CSF, corneal impression smears and centrifuged urine. Inoculation in sucking mice yields results in 1-3 weeks but tissue culture isolation in murine neuroblastoma cells takes about 2 days.
• Indirect immunofluorescence test is not useful for diagnosis since many vaccinated individuals remain positive for antibodies.
• Manson text book of tropical medicine states that corneal impression smears are too insensitive to be useful and false positives have occurred.

Ref: Harrison 19th edition, page 1110
• Pleural effusion in TB could be a presentation of primary TB due to sub-pleural location of Gohn's focus or can present as extra-pulmonary TB.
• Gene XPERT is a nucleic acid amplification based test which in matter of few hours can tell if MTB is present and can also determine resistance.
• The values of LDH are taken in light's criteria for pleural effusion to determine exudative nature of the fluid Adenosine deaminase has 90% sensitivity and 92 % specificity for determining the tubercular nature of fluid.
• The question is based on common sense that albumin values in serum and ascetic fluid are evaluated in patients of ascites.

Ref: Harrison 20th edition, p 1424-27; Harrison 19th, page 770, 1246-47
• The "window period" refers to the maximum amount of time it may take for a person's body to create HIV antibodies after HIV infection. Usually ELISA test turns positive after 3-6 months of infection.
• The p24 antigen test can detect the p24 protein on average 10 to 14 days after infection with HIV.
• One drawback of this test is that levels of the p24 protein peak at around three to four weeks after exposure to HIV and are usually not detectable after five to six weeks (and sometimes even earlier). A positive p24 test means that someone is HIV-positive.
• However, a negative p24 test can mean three things:
 The person is HIV-negative
 The person is HIV-positive but that the test could not detect the p24 protein because the person was infected more than four to six weeks earlier
 The levels of p24 antigen are too low to be detectable with current technologies.
• The HIV NAAT test is a very sensitive test designed to detect HIV RNA in blood. The NAAT test is able to detect 1HV RNA as early as seven to 14 days after infection with HIV Unlike the p24 test, the NAT test will always give a positive result as long as there is HIV in someone's blood.