Blood and insect-borne viruses
30 December 2020 22:08
Physical barriers to viral infection:
• Lysozyme in tears and other secretions
• Skin surface (physical barrier), fatty acids, normal flora
• Rapid pH change
• Removal of particle by cilia in nasopharynx
• Mucus lining trachea
• Stomach (pH 2)
• Normal flora
• Flushing of urinary tract
In blood and insect borne viruses the types of viruses have managed to bypass the skin barrier through
direct injection of the virus into the bloodstream.
Circulatory system:
Arteries: carry oxygenated blood
Veins: carry non-oxygenated blood
Capillaries: 5-10um diameter, allow exchange of water, oxygen, carbon dioxide, nutrients and waste
chemical substances between blood and tissues.
Components of blood
Blood makes up about 8% of total body weight
Whole blood composed of: (55% plasma and 45% formed elements)
Formed elements are mostly erythrocytes (>99%), leukocytes (<1%), platelets (<1%).
Features of blood and insect borne viruses:
Shared features:
• Direct introduction into blood stream
• Require high levels of viremia for transmission
(viremia is the presence of virus in the blood stream)
Not all viruses will make it into the blood stream, some viruses have a very localised replication their
organ/tissue of origin. Other viruses regardless of where they replicate they can make into the
bloodstream.
Unique features:
Different entry routes into blood stream
• Insect bite, skin damage, medical etc.
Cell/tissue tropism may be different
• Blood cells, liver cells etc.
• Tropism: cells/tissues of host that support growth of a particular virus.
Some viruses can replicate in red blood cells whereas some can replicate in other organs cells eg.
hepatocytes.
Clinical symptoms may vary by virus type
Epidemiology
• Direct person-to-person transmission
• Via intermediate host
Direct person to person transmission can be through blood borne viruses and for insect borne viruses
they get transmitted by an intermediate host.
Most common transmission routes for blood-borne viruses:
• Sexual interaction without protection
• Passed from mother to baby via placental route
Blood, Insect-borne viruses Page 1
, • Passed from mother to baby via placental route
• Sharing injecting equipment
• Contaminated blood transfusion and organ transplants
• Virus present in blood, semen and vaginal secretions
• Present in other body fluids only if fluids also contain blood (eg. urine, saliva)
Major blood-borne viruses:
Human immunodeficiency virus (HIV)
• Replicated in blood (immune cells)
Hepatitis B, C and D viruses (HBV, HCV, HDV)
• Replicate in the liver (not in blood)
• Human cytomegalovirus (HCMV)
• Human T-cell lymphotropic virus 1 (HTLV1)
Human Immunodeficiency virus (HIV):
Family: Retroviridae
Genus: Lentivirus
2 types of HIV:
HIV-1 (global)
HIV-2 (West Africa)
Integrates into host genome - Long term persistence infections
Tropism: Immune cells: CD4+ T cells, macrophages and dendritic cells
- Infection results in destruction of CD4+ T cells (immunodeficiency)
Initial infection: mild symptoms
Long incubation period leading to disease: acquired immunodeficiency syndrome (AIDS)
HIV infections are distributed all across the globe, most countries in Africa have higher percentage of HIV
patients.
Acquired immunodeficiency syndrome (AIDS)
Patient suffer from and can die from opportunistic infections (due to immunodeficiency)
- HIV itself does not kill patient
Individuals with AIDS have immune cells less than 200 cells/mm3. This is far below the normal immune
cells level in a healthy individual.
The virus is never cleared from the system as it actually integrate into the human genome. The virus
continues to replicate and destroy some of the CD4+ T cells, which then start to reduce. When the T-cells
reach 200 cells/mm3 the immune system become very immunocompromised and start getting infected
by opportunistic infections and also death eventually.
○ No vaccine
Highly active antiretroviral therapy (HAART)
○ Combination drug therapy
○ Prevents progression to AIDS
○ Not curative
Blood-borne hepatitis virus
Hepatitis C virus:
• Family: Flaviviridae
• Genus: Hepacivirus
Hepatitis B virus:
• Family: Hepadnaviridae
• Genus: Orthohepadnavirus
Hepatitis D virus:
• Viroid (subviral satellite)
Blood, Insect-borne viruses Page 2
30 December 2020 22:08
Physical barriers to viral infection:
• Lysozyme in tears and other secretions
• Skin surface (physical barrier), fatty acids, normal flora
• Rapid pH change
• Removal of particle by cilia in nasopharynx
• Mucus lining trachea
• Stomach (pH 2)
• Normal flora
• Flushing of urinary tract
In blood and insect borne viruses the types of viruses have managed to bypass the skin barrier through
direct injection of the virus into the bloodstream.
Circulatory system:
Arteries: carry oxygenated blood
Veins: carry non-oxygenated blood
Capillaries: 5-10um diameter, allow exchange of water, oxygen, carbon dioxide, nutrients and waste
chemical substances between blood and tissues.
Components of blood
Blood makes up about 8% of total body weight
Whole blood composed of: (55% plasma and 45% formed elements)
Formed elements are mostly erythrocytes (>99%), leukocytes (<1%), platelets (<1%).
Features of blood and insect borne viruses:
Shared features:
• Direct introduction into blood stream
• Require high levels of viremia for transmission
(viremia is the presence of virus in the blood stream)
Not all viruses will make it into the blood stream, some viruses have a very localised replication their
organ/tissue of origin. Other viruses regardless of where they replicate they can make into the
bloodstream.
Unique features:
Different entry routes into blood stream
• Insect bite, skin damage, medical etc.
Cell/tissue tropism may be different
• Blood cells, liver cells etc.
• Tropism: cells/tissues of host that support growth of a particular virus.
Some viruses can replicate in red blood cells whereas some can replicate in other organs cells eg.
hepatocytes.
Clinical symptoms may vary by virus type
Epidemiology
• Direct person-to-person transmission
• Via intermediate host
Direct person to person transmission can be through blood borne viruses and for insect borne viruses
they get transmitted by an intermediate host.
Most common transmission routes for blood-borne viruses:
• Sexual interaction without protection
• Passed from mother to baby via placental route
Blood, Insect-borne viruses Page 1
, • Passed from mother to baby via placental route
• Sharing injecting equipment
• Contaminated blood transfusion and organ transplants
• Virus present in blood, semen and vaginal secretions
• Present in other body fluids only if fluids also contain blood (eg. urine, saliva)
Major blood-borne viruses:
Human immunodeficiency virus (HIV)
• Replicated in blood (immune cells)
Hepatitis B, C and D viruses (HBV, HCV, HDV)
• Replicate in the liver (not in blood)
• Human cytomegalovirus (HCMV)
• Human T-cell lymphotropic virus 1 (HTLV1)
Human Immunodeficiency virus (HIV):
Family: Retroviridae
Genus: Lentivirus
2 types of HIV:
HIV-1 (global)
HIV-2 (West Africa)
Integrates into host genome - Long term persistence infections
Tropism: Immune cells: CD4+ T cells, macrophages and dendritic cells
- Infection results in destruction of CD4+ T cells (immunodeficiency)
Initial infection: mild symptoms
Long incubation period leading to disease: acquired immunodeficiency syndrome (AIDS)
HIV infections are distributed all across the globe, most countries in Africa have higher percentage of HIV
patients.
Acquired immunodeficiency syndrome (AIDS)
Patient suffer from and can die from opportunistic infections (due to immunodeficiency)
- HIV itself does not kill patient
Individuals with AIDS have immune cells less than 200 cells/mm3. This is far below the normal immune
cells level in a healthy individual.
The virus is never cleared from the system as it actually integrate into the human genome. The virus
continues to replicate and destroy some of the CD4+ T cells, which then start to reduce. When the T-cells
reach 200 cells/mm3 the immune system become very immunocompromised and start getting infected
by opportunistic infections and also death eventually.
○ No vaccine
Highly active antiretroviral therapy (HAART)
○ Combination drug therapy
○ Prevents progression to AIDS
○ Not curative
Blood-borne hepatitis virus
Hepatitis C virus:
• Family: Flaviviridae
• Genus: Hepacivirus
Hepatitis B virus:
• Family: Hepadnaviridae
• Genus: Orthohepadnavirus
Hepatitis D virus:
• Viroid (subviral satellite)
Blood, Insect-borne viruses Page 2
