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Blood borne infections
Plasmodium spp
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Five species of
plasmodium cause malaria in humans; ​P
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vivax, P
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knowlesi
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ovale ​some
parasites remain within the liver to lie dormant as hypnozoites which are the cause of
relapses, merozoites in red blood cells mature into the ring form trophozoite and schizont,
which complete the cycle by maturing to release merozoites back into circulation, some
merozoites go on to initiate the sexual stage maturing within red blood cells to form male and
female gametocytes which can be taken up by the anopheles mosquito on feeding, on
entering the gut of the insect the male gametocyte exflagellation to form male microgametes
which fertilise the female gamete to form the zygote, the zygote then invades the gut
mucosa where it develops into an oocyst, the oocyst develops to produce sporozoites which
are released and migrate to the salivary glands of the insect, whence the cycle begins again
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T
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Clinical features of HAT include lymphadenopathy and sleeping sickness
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brucie ​ evades host defenses by varying the antigens in its glycoprotein coat
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cruzi ​ is
transmitted by the reduviid/ triatomine bug and causes chagas disease
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Chronic chagas disease is
usually diagnosed serologically
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Borrelia spp
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Erythema migrans is a
characteristic feature of lyme disease
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Lyme disease is diagnosed serologically and treated
with antibiotics
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Culex spp
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West Nile virus is distributed in Africa, Europe,
Central Asia and the usa
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​Mosquitos
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West Nile virus has a 5% case fatality
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Examples of bloodborne viruses
include; hemorrhagic fever viruses, and human immunodeficiency virus (HIV)
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Viral hepatitis
There are 7 human hepatitis viruses; hepatitis A (HAV, hepatovirus, ssRNA virus, faecal-oral
transmission, 2-4 week incubation period), hepatitis B (HBV, hep adenovirus, dsDNA virus,
blood-borne or sexual transmission, 6 week- 6 month incubation period, carriage associated
with liver cancer), hepatitis C virus (HCV, flavivirus, ssRNA virus, blood-borne transmission,
2 month incubation period, carriage associated with liver cancer), hepatitis D virus (HDV,
deltavirus, ssRNA virus, blood-borne transmission, 2-12 week incubation period, needs
concurrent hepatitis B infection), hepatitis E (HEV, orthohepevirus, ssRNA virus, faecal-oral
transmission, 2-6 week incubation period, sporadic infection, large outbreaks in asia, food
borne, can cause persistent infection in immunocompromised individuals), hepatitis F (HFV,
not associated with with serious pathologies), and hepatitis G (HGV, not associated with
serious pathologies)
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HBV contains a partially double stranded circular DNA genome
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HBV ICTV classification: family-hepadnavirus, genusorthohepadnavirus, species hepatitis B virus
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8 genotypes of HBV have been
classified - A-S
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HBV contains three important antigens; HB surface antigen (HBsAg) the presence of which
indicates infectivity of the blood, HB core antigen (HBcAg), and HBe antigen derived from
HBV core the presence of which indicates high transmissibility and high virulence
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Complications of HBV include cirrhosis and hepatocellular
carcinoma
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The number of HBV carriers worldwide is estimated to be over 350 million
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Certain groups of people are more likely to become carriers of HBV
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However, 10% if infected adults fail to eliminate the virus from the body and
become carriers
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HBV infections are treated with antiviral drugs pegglated interferon and
nucleotide/nucleoside analogues
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HBV infection can be prevented by immunization
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HBsAg is produced in yeast or mammalian cells
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Immunization is recommended for those expressed to
blood or blood products, all healthcare workers, sexual contacts of individuals with acute or
chronic HBV, and injecting drug users
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After accidental exposure to infection, HBIgG can be used to provide
immediate passive protection to immunized individuals
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Human immunodeficiency virus (HIV) that causes AIDS, was isolated from blood
lymphocytes in 1983
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HIV is a retrovirus, a positive sense single stranded RNA virus, characterised by the
possession of virus dependent DNA polymerase (reverse transcriptase)
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HIV targets CD4 receptor bearing cells, including T helper cells, monocytes, langerhan cells,
dendritic cells, macrophages, and microglia
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This interacts with the gp41
transmembrane protein and leads to a conformational change that produces a fusion pore
for viral entry
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HIV-1 enters host cells by binding the viral gp120 to the CD4 receptor and a
chemokine co-receptor on the host cell surface
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Cell
susceptibility to infection is affected by the levels of these chemokines co-receptors
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This is copied by the host cell DNA polymerase to form a double stranded DNA
molecule, which is then integrated into the host cell genome and transcribed resulting in the
production of viral mRNA and progeny RNA virus
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Then the immune
system begins to suffer gradual damage, and the number of circulating CD4 positive T cells
steadily falls and the HIV load rises
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HIV may also be transmitted by intravenous or percutaneous routes
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The main route of transmission is MSM
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heterosexual transmission has not so far been as importnat in
resource rish as in resouce poor countries
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HIV is also
transmitted vertically from infected mothers to babies
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Malaise, maculopapular rash, and lymphadenopathy
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At a later stage
the infected individual may develop weight loss, fever, persistent lymphadenopathy, oral
candidiasis and diarrhea
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A progressive HIV-associated encephalopathy is seen in
individuals with AIDS and is characterized by multiple small nodules of inflammatory cells,
most of the infected cells appear to be microglia on infiltrating macrophages
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AIDS,
symptomatic disease, consists of a large spectrum of microbial diseases acquired or
reactivated as a result of the underlying immunosuppression due to HIV
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Initial laboratory diagnosis is based on detection of antibodies of surface glycoprotein gp120
and gp41
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HIV-1 RNA or proviral DNA test may be
carried out on plasma and whole blood samples, respectively
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In addition, part of the
laboratory portfolio involves antiretroviral resistance genotype analysis by automated DNA
sequencing
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Antiretroviral therapy results in a dramatic improvement in disease prognosis
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Treatment combines individual classes and combinations
of classes
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Specific mutations in the HIV reverse transcriptase, protease and integrase regions
associated with reduced susceptibility to one or more antiretroviral drugs have been
identified by nucleic acid sequencing
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Transmission of drug-resistance HIV is an important issue
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treatment of AIDS involves prophylaxis and treatment of opportunistic infections as well as
using antiretrovirals
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reducing sexual
transmission by changing sexual behaviour and condom use is a major public health effect,
but pee-exposure prophylaxis with daily antiretroviral therapy has been shown to reduce HIV
transmission
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The risk of transmitting

HIV via blood and blood products is reduced by donto screening programs and heat
treatment
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