Onset of the infection
The time between the exposure to the virus and the development of symptoms or the incubation period is between 2 to 21 days and usually between 4 to 10 days, respectively. Symptoms usually involve an onset of a flu-like stage which is mainly characterized by tiredness, fever, weakness, decreased appetite, muscular pain, joint pain, headache, and sore throat. The body temperature during fever is usually higher than 101 °F or 38.3 °C. This is often followed by vomiting, diarrhea, and abdominal pain. Next, shortness of breath and chest pain may occur, along with swelling, headaches and confusion. In about 50% of the cases, the skin may develop a flat red area covered with bumps also known as maculopapular rash, 5 to 7 days after symptoms begin.
Bleeding during the infection
Internal and external bleeding is seen in some people. This typically begins five to seven days after the first symptoms. The clotting factors decrease in the infected people which eventually leads to a decrease in the blood clotting time. Bleeding from mucous membranes or from sites of needle punctures has been reported in half of the cases. This may cause vomiting blood, coughing up of blood, or blood in the stool. Bleeding into the skin may create petechiae, purpura, ecchymoses or hematomas (especially around needle injection sites). Bleeding into the whites of the eyes may also occur. Heavy bleeding is uncommon; if it occurs, it is usually located within the gastrointestinal tract.
Recovery and death
Within 7 to 14 days of the appearance of initial symptoms, recovery may be seen. In people with severe fluid loss, there is a significant drop in the blood pressure which eventually leads to death. The occurrence of death is seen between 6 to 16 days of the appearance of the first symptoms. In general, bleeding doesn’t result in a good outcome as the patient might even end up being in the coma during the last stages of the disease. The people infected for a longer duration usually show signs of weakness, tiredness, and vision-related problems, decreased appetite, muscle and joint pains, liver inflammation and also decreased hearing. On exposure to Ebola virus, antibodies are developed by the immune system which can last for up to 10 years in the system. But, their effect in providing immunity on a second exposure to the disease is unclear.
Ebola virus (EBOV) which was previously known as Zaire ebolavirus is one of the five viruses in the genus Ebolavirus. EBOV has a single-stranded RNA in the genome. Ebolavirus genomes contain seven genes including 3'-UTR-NP-VP35-VP40-GP-VP30-VP24-L-5'-UTR. The genomes of all the ebolaviruses have variations in their sequences and the locations of the gene overlap also vary. The virions are 80 nm in width and up to 14,000 nm in length. They are filamentous in nature and have the shape of a shepherd's crook, of a "U" or of a "6,” They can also be either coiled, toroid or branched.
The image below is of the Ebola Virus under an electron microscope (Source: Wikipedia).
This below is an illustration of the structure of Ebola virus (source: ukaye.wordpress.com).
Pathophysiology of the infection
EBOV replicates very efficiently in a wide range of cells like monocytes, macrophages, dendritic cells, hepatic cells, fibroblasts and adrenal gland cells. A state of sepsis is induced due to the inflammatory response and chemical signals triggered by the viral replication. Following infection with the virus, the virus-infected host cells carry the virus to the lymph nodes where the virus replicates itself to further the infection to the next stage. The lymphatic system and bloodstream are infected in this process and thus, carrying the virus to all parts of the body. Macrophages are the first cells infected with the virus, and this infection results in programmed cell death. Lymphocytes are also targeted by EBOV which lowers their count due to programmed cell death. Other types of white blood cells, such as lymphocytes, also undergo programmed cell death leading to an abnormally low concentration of lymphocytes in the blood and thus the immune system is weakened. The lower count of lymphocytes is a factor that is observed while diagnosing for EVD.
Endothelial cells are infected within the first 3 days of exposure and their breakdown which leads to blood vessel injury can be caused by the EBOV glycoproteins. Liver damage and improper clotting are observed due to the lack of the specific integrins which are responsible for cell adhesion to the intercellular structure. The affected people experience shock, and swelling is also seen due to the blood loss. There is an increase in the activation of the extrinsic pathway of the coagulation cascade which attributes to the dysfunctional bleeding and clotting as there is excessive tissue factor that is produced by macrophages and monocytes.
After infection, a small soluble glycoprotein (sGP or GP) is synthesized. The protein synthesis in the infected cells of the immune system is overwhelmed by the EBOV replication. A trimeric complex is formed between the GP and the endothelial cells. The signaling of neutrophils in intercepted by a dimeric protein formed by the sGP which aids the virus in evading the immune response as the activation of the neutrophils in nipped in the early stages. The presence of viral particles and the cell damage resulting from viruses budding out of the cell causes the release of chemical signals (such as TNF-α, IL-6, and IL-8), which are molecular signals for fever and inflammation.
Diagnosis of the disease
Laboratory diagnosis includes:-
1. A low platelet count and an initial decrease in the white blood cells, specifically lymphocytes is observed.
2. Elevated levels of liver enzymes like alanine aminotransferase (ALT) and aspartate aminotransferase (AST) is observed.
3. There are certain abnormalities in the clotting of the blood like prolonged prothrombin time, partial thromboplastin time and bleeding time.
4.Though the virus can be observed under an electron microscope, this method cannot be used for diagnosis as the differentiation of various filoviruses is not possible.
5. Detection of specific RNA or proteins post isolation of the virus and the detection of antibodies in the blood is performed as a part of the specific diagnosis. The positive results in any of the above diagnostic methods are taken as a confirmation to being infected with the virus.
6. Isolation of the virus by cell culture, detection of the viral RNA by polymerase chain reaction (PCR) and the detection of proteins by enzyme-linked immunosorbent assay (ELISA) are used as diagnostic tools during the early stages of the infection.
7. Later detection is done by identifying antibodies in the blood of the infected people and in the blood of those who recover from the infection.
8. Detection of IgM and IgG during the onset of the infection, i.e., between 2 days and 6 to 18 days respectively.
9. Real-time PCR and ELISA are the two diagnostic tools which are considered to be the most effective in giving quick results.
Providing the right care in terms of oral rehydration solutions and intravenous fluids to infected people to prevent the massive fluid loss is one way to counter the symptoms and improve the survival. There is as yet no proven treatment available for EVD. However, potential treatments include blood products, immune therapies, and drug therapies. No licensed vaccines are available yet, but two potential vaccines are undergoing human safety testing.
Risk reduction should focus on several factors like:-
1. Reducing the risk of wildlife-to-human transmission- animals should be handled appropriately and the meat should be thoroughly cooked prior to consumption.
2. Reducing the risk of human-to-human transmission- people should be made aware of how to handle the body fluids of the infected patients. Gloves should be worn at all times while handling patients and hand washing should be frequent after visiting patients in the hospital or at home.
3. Reducing the risk of possible sexual transmission- the people recovering from Ebola are often advised to abstain from sex of all types for at least 3 months since the onset of symptoms. if abstinence is not possible, protection during sex is the only way to prevent sexual transmission. Washing hands and intimate areas are also of importance to prevent the spread of Ebola.
4. Outbreak containment measures- the virus is active in the corpses which make it mandatory to follow safe burial practices to avoid the spread of the disease. the people who have come in contact with the dead are monitored for the initial symptoms to prevent the spread if they are infected.
5. Health-care workers should always take standard precautions like wearing protective equipment and also follow safe injection and safe burial practices.
6. Extra care should be taken if the patient is diagnosed positive for Ebola. The handling of the body fluids, clothing and bedding should be thorough. Wearing a protective mask, gloves and body cover while around such cases is always advised.
7. Laboratory workers are also at risk. Samples taken from humans and animals for investigation of Ebola infection should be handled by trained staff and processed in suitably equipped laboratories.