Question

Case Study, Mechanisms of Infectious Disease

35 –year-old Mark is a construction worker, who fell ill shortly after working on a job digging up old water pipes for the town he lived in. The task involved working around shallow pools of stagnant water. A week and a half after the contract ended, Mark developed a fever and aching muscles, with nausea, vomiting, a rash and diarrhea. Mark’s friend took him to the hospital where a doctor listened carefully to his history. The doctor told him that she suspected West Nile fever and ordered serologic testing. Mark was discharged and went home to recover and was feeling better by the end of the week.

1. Mark’s physician ordered serologic tests. How would antibody titers assist the doctor in confirming his diagnosis?

2. When Mark was feeling at his worst, he had extreme malaise, vomiting, and diarrhea. What stage of the illness was he experiencing at that time? What are the physiologic mechanisms that give rise to the signs and symptoms of infectious illness?

3. West Nile virus has a single-stranded RNA genome. How does this virus replicate? In general terms, what are the various effects viruses can have on host cells?

Answer 1

West Nile fever is an infection transmitted by mosquitoes mostly species of Culex . The causative organism is a virus known as West Nile virus which is a a single-stranded RNA virus from the family of  Flaviviridae. The virus enter into the body and spread in the blood and multiply, which can cause serious neurological symptoms once it enter in the brain.

1. The body produce specific antibodies towards West Nile virus, they are specific IgM antibodies . Thus, by doing serologic antibody titers can easily detect the presence of these virus specific IgM antibodies and make the diagnosis easy for the doctor.

2. The West Nile virus can affect an individual in three different ways or categories. The first stge is asymptomatic stage where the patient will not experience any signs and symptoms of infection. The second stage is the people who are affected will develop symptoms like fever, fatigue, skin rash, diarrhea, nausea, headache, vomiting, swollen lymph glands, and muscle or joint pains which may last for few days to weeks. In the third category, if the infected individual who has weak immune system may develop serious brain involvement with encephalitis or meningitis with the symptoms like severe headache, high fever, stiff neck, disorientation, seizures, tremors, muscle weakness, lose of coordination, and coma and eventually death.As Mark has symptoms like fever and aching muscles, nausea, vomiting, a rash and diarrhea, he is in the second stage or category.

He is experiencing the symptoms due to the humoral immune response of the body. When the virus enter into the body and start to multiply, the body start to produce the specific IgM antibodies against the virus which cause inflammation and cell damage. As a result of the byproducts produced by the viral destruction and cellular damage, the body shows flu like symptoms which are marker symptoms for all common infections.

3. The replication of virus

Once the virus reach near to the cell membrane, the virus get attatched to the cell membrane with the help of cellular receptors and the viron envolop get fused to the cell membrane known as clathrin-mediated endocytosis. Then the virus release the RNA genome into the cytoplasm which serves as a messenger RNA during RNA replication for translation of all viral proteins. After viral assembly and morphogenesis, the new replicated copies of virus are transported with in the packed vesicles to cell membrane and release them to extracellular fluid.

The host cell will be affected in different ways as the multiplication of the virus leads to immune response involving cell lysis, apoptosis and cell death. Uncontrolled viral proliferation can damage the immune system, once the immune system get exhausted, it leads to impaired immunity levels and infections. The cellular changes can leads to abnormal proliferation of damaged cells which may leads to cancer or giant tumor formation. Invasion of virus to brain through blood brain barrier can cause serious nerve tissue damage and fatal effects.