MLT GlobeDHA exam preparation (Dubai) – page 19
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
Premunition (concomitant immunity), in which resistance to reinfection persists only while low-level infection remains, is classically seen in:
In malaria-endemic areas, persistent low-grade parasitaemia maintains partial immunity; it wanes when parasites are cleared.
Which statement about cutaneous leishmaniasis is incorrect?
Cutaneous leishmaniasis is spread by phlebotomine sandflies, not mosquitoes. Lesion smears show amastigotes, L. major causes Old World disease, and L. mexicana/braziliensis complexes occur in the Americas.
Recrudescence in falciparum malaria is best explained by:
Recrudescence is a renewed attack from surviving erythrocytic parasites, often after incomplete treatment. Relapse from hypnozoites applies to P. vivax and P. ovale; a new bite is reinfection.
Blackwater fever in falciparum malaria results from:
Sudden widespread intravascular hemolysis releases free hemoglobin that is filtered into urine, making it dark. Capillary blockage underlies cerebral malaria, not blackwater fever.
In bancroftian filariasis, which stage is chiefly responsible for lymphatic damage?
Adult worms and the host reaction to them (including dying adults and Wolbachia antigens) cause lymphatic dilation and blockage. Microfilariae mainly matter for transmission and diagnosis.
In a Leishmania promastigote, the free flagellum arises from which part of the cell?
Promastigotes are elongated with the kinetoplast and basal body near the front, and a free flagellum projects from the anterior end. Amastigotes lack a free flagellum.
The main reservoir hosts of Leishmania major are:
L. major is a zoonosis maintained in desert rodents like gerbils. Dogs are the main reservoir for L. infantum (visceral leishmaniasis).
Cutaneous leishmaniasis in the Americas is transmitted by sandflies of the genus:
New World sandflies belong to Lutzomyia, while Old World vectors are Phlebotomus. Glossina is the tsetse fly.
A gardener gets a nodule after a thorn prick, followed by a chain of nodules along the lymphatics of the arm. The most likely cause is:
Sporothrix schenckii enters via minor trauma and spreads along lymphatics (lymphocutaneous sporotrichosis). Tinea capitis affects the scalp and cryptococcosis is mainly acquired by inhalation.
To check for CNS involvement (stage 2) in African trypanosomiasis, which specimen is examined?
CSF is tested for trypanosomes and raised white cells to stage the disease, which guides treatment choice. Blood and lymph node aspirates detect early infection.
Humans acquire all of the following from pigs or dogs except:
A. lumbricoides spreads person to person through eggs in fecally contaminated soil. Echinococcus comes from dogs, and T. solium and Trichinella from pigs.
The mature cyst of Entamoeba histolytica usually measures about:
E. histolytica cysts are 10 to 20 micrometers with up to four nuclei. Cysts under 10 micrometers suggest E. hartmanni, so an ocular micrometer is needed.
When antibody-coated target cells are lysed by complement, which component polymerizes to form the pore in the membrane?
C5b-8 inserts into the membrane and recruits many C9 molecules, which polymerize into a pore. C1q binds antibody and C3b opsonizes.
The antibodies produced in a normal immune response to a protein antigen are NOT:
A natural response is polyclonal, so antibodies vary in sequence and specificity. A single sequence is a feature of monoclonal antibodies.
What is the role of the J chain in immunoglobulins?
Plasma cells produce the J chain, which joins IgM pentamers and IgA dimers and enables transport across epithelium.
A person who cannot make J chain would lack secretory IgA. Recurrent infections would most likely involve the:
Without J chain, polymeric IgA cannot be transported by the polymeric Ig receptor to mucosal surfaces such as the gut.
The CD3 complex associated with the T-cell receptor:
CD3 (formerly T3) transmits activation signals when the TCR binds peptide–MHC.
Which statement about the CD4 and CD8 markers is FALSE?
Mature peripheral T cells express either CD4 or CD8; double-positive cells occur only in the thymus.
A single immunoglobulin-type domain, found in antibodies and TCRs, contains roughly how many amino acids?
Immunoglobulin domains are about 110 amino acids, folded and stabilized by a disulfide bond.
Which HLA allele is most strongly associated with rheumatoid arthritis?
HLA-DR4 (shared epitope) is linked to RA. HLA-B27 is linked to ankylosing spondylitis and DQ2 to coeliac disease.