Course info

Viral Infections

The virus

 

A virus is a very small but very infectious organism that needs to attach itself to a host cell injecting its DNA or RNA to replicate.

 

 

Parts of a virus:

1. Genetic material – DNA or RNA

2. Protein coat – protects the DNA or RNA

3. Envelop of lipid – surrounds the protein coat when they are outside a cell

 

 

Mechanism of infection:

1. The virus attaches its DNA or RNA and forces its host cell to replicate the virus. The cell usually dies and releases a new virus.

2. Some viruses do not kill the cells but only alter the cell’s functions. When the infected cell losses control, it becomes cancerous.

3. Some viruses leave their DNA or RNA in the host cell and become dormant for a long time (latent infection). When the cell is disturbed, the virus begins to replicate and cause disease.

4. Cold viruses constantly mutate that the immune system finds it difficult to detect.

5. Chicken pox viruses can become inactive before they are destroyed by the immune system. They become dormant and can come back later in the form of shingles when the body is physically and emotionally stressed.

6. Herpes simplex viruses can hide in the neurones where the immune system can not find them. When they are disturbed by stress or hormones, they travel to the skin destroying them and cause blisters.

7. Human Immuno Virus (HIV) kills the T cells and consequently making the body susceptible to more infection.

 

 

Mechanism of body’s defence: The immune system response

1. The white blood cells or macrophages destroy the viruses before they can infect the cells.

2. B cells and T cells (lymphocytes) are more powerful defence that fight when infection has started.

3. Antibodies are proteins that are produced by B cells to help stop the viruses from replicating by binding into them.

4. T cells are like guard dogs that raise the alarm upon detection of viruses. Some can directly kill an infected cell. Some help B cells to produce more antibodies.

5. After the infection has been fought off, the B cells and T cells can retain a memory of the destroyed virus so that the body is not infected by the same virus twice. This is called the acquired immunity.

Some of the common viral infection in children:

Viral Infection	Incubation Period	Site of Rash	Characteristic
Varicella (Chicken pox)	11-15 Days	Appear first in the face and trunk then later in the neck, arms and legs	Small, flat, red sores that become raised and filled with fluid. Infection lasts a few days to 2 weeks. Blisters crust after a few days.
Rubeola (Measles)	7 – 14 days	Starts around the ears, face and neck. In severe cases may spread over the trunk, arms and legs.	Rashes start to appear 3 to 5 days after the onset of symptoms and lasts 3 to 5 days. Rashes are red, irregular, flat and later become raised. Measles is contagious from 2 to 4 days before the rashes appear until 2 to 5 days after.
Rubella (German Measles)	14- 21 days	Starts from the face and neck the spread to the trunk, arms and legs.	Rashes are fine, flat and pinkish. Rashes appear from 1 to 2 days after the onset of symptoms and lasts from 3 to days. German measles is contagious shortly after the appearance of rashes until they disappear.
Roseola infantum (exanthem subitum or pseudorubella)	5 to 15 days	Chest, abdomen, may also involve face, arms, and legs	Rashes are red and flat. They start to appear from the 4th day after temperature drops to normal and they usually lasts for a few hours to 2 days.
Erythema infectiosum (fifth disease or parvovirus B19)	4 to 14 days	Start in the cheeks then spread to the arms, legs and trunk.	Rashes are red and flat with raised areas, often blotchy with lacy patterns. Lasts for 5 to 10 days.
Coxsakie virus (Hand and Foot Disease)	1-2 days	Small and painful blisters in the palms of the hand, soles of the feet and in the mouth.	The blisters develop 1-2 days after the fever. Sore throat and malaise may also occur. Duration of illness is 7-10 but the infected person may be contagious for several weeks.

Herpes Simplex 1 (Oral Herpes/ Cold Sores/ Fever Blisters)

 

These are small and painful fluid-filled blisters or sores that appear in the lips, mouth, throat, cheek, chin, nose or fingers.

 

Causative agent – Herpes Simplex virus type 1

Incubation period – 2 to 12 days

Duration of illness – Symptoms may last until 2 to 3 weeks

Symptoms- pain, burning, itching and tingling sensation (prodromal stage) that is followed by blister after 1 or 2 days. The blisters then break open leaking clear fluid then crust and can last for 2-24 days.

The blisters – They appear as tiny, shallow gray ulcers on a red base and they break rapidly. After a few days, they crust or scab, becomes dry and yellowish.

 

Transmission – Person to person by kissing or close contact with the sores. Self-inoculation can happen by touching the skin that is shedding the virus. Washing the hands with soap and water can prevent transmission. Once the virus has entered and infected the body, it remains dormant and will cause infection when the immune system is low.

Treatment:

1. Treat fever.

2. Topical anesthetic.

3. Antiviral drugs – they stop replication of virus in the skin but they do not eliminate the virus from the body and they also not prevent future occurrences of attacks

· Topical acyclovir creams can shorten the disease when applied before the sore begins

· Acyclovir tablets – 200mg 5x daily 4 hourly during the day

 

· Famciclovir – 500mg BID 7 days

· Valacyclovir (Valtrex Film-coated 500mg) – 500mg BID 10days(initial episode). For recurrent episodes 500mg BID 5 days.

Prevention of recurrence: 500mg OD

 

 

Herpes Simplex 2 (Genital Herpes)

Genital herpes is the most common STD and a highly infectious disease because the virus can enter the body not only through sexual intercourse but also through skin on skin contact to even a very small lesion. An infected person may be asymptomatic but during sexual contact, the disease can be transmitted.

Symptoms – Fever. Blisters or open sores on and around the genitals in both men and women. Tender and swollen lymp nodes in the groin. May last up to 2 to 4 weeks.

Location of blisters – May be found in or around the genitals and the anus. In female, they may be found inside the vagina causing discharge and may not be seen except during a doctor’s physical examination.

Causative agent – Herpes Simplex virus type 2

Transmission – Sexual contact

Incubation period – 3 to 7 days

Treatment:

1. Treat fever.

2. Topical anesthetic.

3. Antiviral drugs – they stop replication of virus in the skin but they do not eliminate the virus from the body and they also not prevent future occurrences of attacks

· Topical acyclovir creams can shorten the disease when applied before the sore begins

· Acyclovir tablets – 200mg 5x daily 4 hourly during the day. Prophylaxis and for very frequently recurring genital herpes – 200mg 4 times daily 6 hourly.

· Famciclovir – 500mg BID 7 days

· Valaciclovir (Valtrex Film-coated 500mg) – 500mg BID 10days(initial episode). For recurrent episodes 500mg BID 5 days.

Prevention of recurrence: 500mg OD

Ebola hemorrhagic fever aka Ebola virus disease

This is considered as one of the most lethal viral infection. The four Ebola strains are termed as follows: Zaire, Sudan, Tai Forest, and Bundibugyo virus, with Zaire being the most lethal strain.

 

 

Transmission – A direct contact with blood, feces or body fluids from an infected person.

Incubation period – 2 to 21 days

Symptoms: High fever, headache, muscle pain, stomach pain, sore throat, weakness

May progress to: diarrhea, vomiting, stomach pain, hiccups, rash, and internal and external bleeding like epistaxis (nose bleeding), hemoptysis (spiting blood from the lungs) , hematemesis (vomiting blood from the stomach), bloody eyes (conjunctival hemorrhages).

Treatment: Supportive therapy. Balancing fluid and electrolytes, maintain oxygen level and blood pressure, and treat complications. Death can occur within 10 days of the onset of symptoms.

How can Ebola hemorrhagic fever lead to death?

It is discovered that Ebola virus has a protein on its surface that is responsible for severe bleeding. The protein attacks and destroys the endothelial cells lining the blood vessels so they leak and bleed.

When inside the body, Ebola virus causes coagulation abnormalities, rash, and cytokine release. It also causes damage to the liver. A large number of viruses in the blood (viremia) compromise the coagulation factors and damage endothelial cells leading to massive bleeding internally then externally. This uncontrolled bleeding results to blood and fluid loss then hypotensive shock then death.

Diagnosis - There is no specific diagnosis for Ebola virus infection. It begins when the patient manifests the described symptoms and has been exposed to individuals with Ebola virus. A few days after, ELISA and PCR tests and virus isolation can further confirm diagnosis. After recovery, IgM and IgG antibodies against Ebola can be detected.