Page 340 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 39 RNA Enveloped Viruses
329
neurons in the spinal cord. HAM is caused either by an
autoimmune cross-reaction in which the immune response
Infection with HTLV is determined by detecting antibodies
against HTLV damages the neurons or by cytotoxic T cells
against the virus in the patient’s serum using the ELISA test.
that kill HTLV-infected neurons.
The Western blot assay is used to confirm a positive ELISA
result. PCR assay can detect the presence of HTLV RNA or
Clinical Findings
ATL is characterized by lymphadenopathy, hepatospleno-
screen donated blood contain only HTLV-1 antigens, but
megaly, lytic bone lesions, and skin lesions. These features
because there is cross-reactivity between HTLV-1 and
are caused by proliferating T cells infiltrating these organs. DNA within infected cells. The laboratory tests used to
HTLV-2, the presence of antibodies against both viruses is
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usually detected. However, some HTLV-2 antibodies are
In the blood, the malignant T cells have a distinct “flower-
shaped” nucleus. Hypercalcemia due to increased osteoclast
missed in these routine screening tests. Isolation of HTLV in
cell culture from the patient’s specimens is not done.
activity within the bone lesions is seen. Patients with ATL
ATL is diagnosed by finding malignant T cells in the
often have reduced cell-mediated immunity, and opportu-
nistic infections with fungi and viruses are common.
The clinical features of HAM include gait disturbance,
ence of HTLV antibody in the spinal fluid or finding HTLV
nucleic acids in cells in the spinal fluid.
weakness of the lower limbs, and low back pain. Loss of
bowel and bladder control may occur. Loss of motor func-
tion is much greater than sensory loss. T cells with a
Treatment & Prevention
“flower-shaped” nucleus can be found in the spinal fluid.
Magnetic resonance imaging of the brain shows nonspe-
cific findings. Progression of symptoms occurs slowly over
and no antiviral drug will cure latent infections by HTLV.
ATL is treated with anticancer chemotherapy regimens.
a period of years. HAM occurs primarily in women of There is no specific antiviral treatment for HTLV infection,
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middle age. The disease resembles multiple sclerosis except
Antiviral drugs have not been effective in the treatment of
that HAM does not exhibit the remissions characteristic of
HAM. Corticosteroids and danazol have produced
improvement in some patients.
multiple sclerosis.
Both ATL and HAM are relatively rare diseases. The vast
There is no vaccine against HTLV. Preventive measures
majority of people infected with HTLV develop asymptom-
atic infections, usually detected by the presence of anti-
bodies, using condoms to prevent sexual transmission, and
body. Only a small subset of those infected develop either
encouraging women with HTLV antibodies to refrain from
ATL or HAM.
breast feeding.
FILOVIRUSES
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There are two important filoviruses that cause human
disease: Ebola virus and Marburg virus. Filoviruses are
long filamentous (filo = thread) viruses. They are the lon-
gest viruses, often measuring thousands of nanometers
(Figure 39–7).
EBOLA VIRUS
Disease
Ebola virus causes Ebola hemorrhagic fever (EHF). The
virus is named for the river in Zaire that was the site of
the first known outbreak of EHF in 1976. A devastating
epidemic of EHF occurred in several West African coun-
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tries, especially Liberia, Sierra Leone, and Guinea in
2014–2015.
points to a typical virion of Ebola virus. Short arrow points to the
Important Properties
“shepherd’s crook” appearance of some Ebola virions. (Source: Dr. Erskine
Ebola virus has a single-stranded, nonsegmented, negative
Palmer and Dr. Russell Regnery, Public Health Image Library, Centers for Disease
polarity RNA genome. There is an RNA-dependent RNA
Control and Prevention.)

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