Background: Ebola virus causes a hemorrhagic fever that is often fatal. The disease was first reported in 1976 in the Democratic Republic of the Congo (formerly Zaire), and outbreaks have appeared sporadically since then. The disease progresses quickly upon infection, usually in 2-10 days. The symptoms begin with fever, headache, and muscle aches, followed by diarrhea and vomiting. In severe cases, internal and external bleeding occur. The virus is spread from person to person via contact with infected blood or secretions. The source of the initial infection in an outbreak is not known, but it is hypothesized to be transmitted from an infected animal. The infection can be diagnosed within a few days of the onset of symptoms, using an ELISA to test for Ebola virus proteins or RT-PCR to test for virus genetic material. (Since the virus genetic material is RNA, reverse transcriptase (RT) is used to copy the RNA into cDNA for the PCR test). After recovery, patients can be tested for antibodies to Ebola virus proteins in their blood to confirm infection. There is no treatment for Ebola hemorrhagic fever other than supportive care. The death rate from infection is typically 70-80%. There is no vaccine available for Ebola virus.
Note: An ELISA test is considered positive if the color production (absorbance) for a sample is at least twice the negative control value. PCR results are recorded as viral load values, i.e. how many copies of the virus were detected.
Case A. An outbreak of a disease that resembles Ebola hemorrhagic fever has been reported in a village outside of Kinshasa, the capital of the Democratic Republic of Congo. Local health officials are concerned about the outbreak spreading to such a large population. Health workers are sent to the village to determine whether the disease is caused by Ebola virus. Most of the victims so far belong to one family. Blood samples are collected from the family members showing symptoms of hemorrhagic fever and tested for Ebola virus proteins and genetic material.
Procedure: To analyze this case, run an ELISA on the proteins in throat blood samples from the various family members, as well as a PCR test on cDNA isolated from the samples.
Protein and DNA samples:
- Negative control
- Positive control for Ebola
- Mother
- Father
- Son
- Daughter
- Grandmother
- Are these family members infected with Ebola virus?
- What should be done for these individuals if they are infected?
- What precautions should be taken when handling these blood samples?
- What should be done to prevent the virus from spreading to the city of Kinshasa?
Case B. One of the animals suspected of being a reservoir for Ebola virus is the fruit bat. After an outbreak of Ebola hemorrhagic fever in Gabon, scientists captured dozens of bats in the forests near the village and tested their blood for antibodies to Ebola virus. The presence of Ebola antibodies would indicate that the bats had been infected with Ebola at some time and survived. None of the bats were showing symptoms of hemorrhagic fever at the time they were captured.
Procedure: To analyze this case, run an ELISA on the 10 bat blood samples provided, testing them for antibodies to Ebola proteins. If any of the samples test positive for antibodies, test those samples for Ebola cDNA by PCR.
- How many bats, if any, tested positive for Ebola antibodies?
- Did any samples test positive for Ebola genetic material? What does a positive result mean?
- Does a positive result mean that bats started the Ebola outbreak in Gabon?
- If bats test positive for Ebola, should efforts be made to eliminate bats in areas near human populations?