Answer
Mode of spread from mother to offspring :
1- Congenital : from mother s blood through the
placenta to the fetus ( i.e. transplacental passage
of the virus ).
2- Intranatal :
during birth from transplacental bleeding or contact of
abrasions with virus containing fluids ( cervical secretions
& blood ) during passage along the birth canal.
3- Early postnatal :
through breast milk.
T helper-inducer lymphocyte ( CD4 Lymphocyte ).
- HIV infection attacks CD4 helper cell leading to their
depletion the cellis affected both qualitatively & quantitatively
by HIV infection( i.e. the virus is lytic to the infected cells ).
the consequences of T cell dysfunction & depletion are
devastating because the CD4 Lymphocyte plays a critical
role in the human immune response.
the treatment of AIDS slow the progression of the disease
( delay the appearance of symptoms & signs )
( the incubation period of AIDS may be more than 7 years ).
Medications:
* Zidovudine ( formerly Azidothymidine, AZT )
- can be used as monotherapy or in combination with other
nucleotide Analogs ( e.g. zalcitabine or didanosine ) .
* mechanism of actioin :
AZT inhibits the reverse transcriptase & after incorporation
into DNA, causes chain termination.
Work Step by Step
Acquired Immune Deficiency Syndrome ( AIDS )
Definition
communicable disease characterized by profound
immunosuppresion associated with opportunistic
infection & development of certain tumors specially
Kaposi s sarcoma.
Pathogenesis
- human immunodeficiency virus ( HIV ) attacks CD4
helper cells leading to their depletion.
the CD4 molecules on these cells are the major
receptors for virus glycoproteins ( attachment site ).
fusin & CCR5 proteins on human cells ( chemokine
receptors ) are coreceptors required for entry of
HIV into CD4 +ve cells.
- the cardinal feature of HIV infection is the depletion
of T helper-inducer lymphocyte ( CD4 lymphocyte)
which is affected both qualitatively & quantitatively
by HIV infection i.e. the virus is lytic to the infected
cell & so the cell count drops significantly.
the consequences of T cell dysfunction & depletion
are devastating because the CD4 lymphocyte plays
a critical role in the human immune response.
- Another mechanism hypothesized to explain the
death of T helper cells is that HIV acts as
a " superantigen " which indiscriminately activates
many T helper cells & lead to their demise.
Mode of Transmission of HIV
I- Horizontal Transmission:
a- Sexual Transmission :( hetero &homosexual)
other sexually transmitted diseases especially
genital ulcer disease increase the risk of sexual
transmission as much as a hundred fold.
b- Blood & Blood Products :
transfusion of infection , blood or blood products
is an effective route for HIV transmission.
transmission due to sharing of contaminated
syringe needle occur mainly in intravenous drug
abusers.
II- Vertical Transmission :
a- Congenital :
i.e. from mother s blood through the placenta to
the fetus (= transplacental passage of the virus ).
b- Intranatal :
during birth from transplacental bleeding or
contact of abrasions with virus containing fluids
( cervical secretions & blood ) during passage
along the birth canal.
c- Early Postnatal :
- mainly through breast milk .
- such mothers should not breast feed.
N.B
saliva, causal contact & insect bites proved to be
non-infectious.
Clinical Manifestations
- the incubation period varies from 6 months to
7 years or more,
infected neonates develop symptoms by 2 years.
- AIDS related complex ( ARC ) may preceed AIDS
& is characterized by fatigue,chronic diarrhea, oral
candidiasis & persistent lymphadenopathy.
- in its full blown picture , AIDS manifests by :
1- infections with opportunistic organisms :
a- Protozoa : Pneumocystis carinii, toxoplasma
gondii.
b- Fungi : Candida albicans, Cryptococcus
neoformans.
c- Bacteria : M.avium, M.tuberculosis, Listeria
monocytogenes.
d- Viruses : CMV, Herpes simplex virus, hepatitis
B virus.
2- Malignancies :
Kaposi s sarcoma & malignant lymphoma.
3- Neurological Manifestations :
e.g. subacute encephalitis, dementia, &
encephalopathy.
Laboratory Diagnosis
1- Decreased numbers of CD4 cells below 400/cubic
millimeter in the late stages & inversion of CD4/CD8
ratio.
2- Detection of HIV in test samples by polymerase
chain reaction ( PCR )
one HIV infected cell in a million can be detected.
3- Isolation of the virus from lymphocytes, bone
marrow or plasma on tissue culture.
4- Detection of HIV antibodies by ELISA :
A positive test must be repeated & confirmed by
Western blot technique before being notified.
Western blot technique is a more specific test that
detects antibodies against core protein p24 or
envelope glycoproteins gp41, gp120.
Treatment
- Zidovudine,( formerly azidothymidine, AZT ) is the
best anti-HIV drug available, which can be used
either as a monotherapy or in combination with
other nucleotide analogs ( e.g.Zalcitabine or
Didanosine ).
- AZT inhibits the reverse transcriptase & after
incorporation into DNA, causes chain termination.
- Although, it clearly benefits at least for many months
its use is limited by its bone marrow toxicity.
- Other nucleotide analogs, including didanosine
( dideoxyinosine ) & zalcitabine ( dideoxycytidine )
are also being used against HIV infection.
- additional approaches to HIV chemotherapy include
CD4 receptor analogs & interferon inducers.
