Lassa fever pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]; Associate Editor(s)-in-Chief: Ammu Susheela, M.D. [3]
Synonyms and keywords: Lassa hemorrhagic fever; LHF
Overview
Lassa fever is a zoonotic disease caused by Lassa virus and spread by multimammate rat vector. It is spread through person-to-person contact, direct contact with rodent excretion and after an incubation period of 1-24 days can manifest as fever, muscle aches, sore throat, nausea, vomiting, chest and abdominal pain, weakness, cough, headache, exudative pharyngitis, anemia, low blood pressure, and diarrhea.
Pathophysiology
Pathogenesis
- Lassa virus infects the endothelial cells and perturbation of vascular function is likely to be central to Lassa fever-associated pathobiology, since the signs of increased vascular permeability, such as facial edema and pleural and pericardial effusions, indicate a poor prognosis for the disease outcome.
- Failure to develop the cellular immune response that would control dissemination of LASV, which is indicated by high serum virus titers, combined with disseminated replication in tissues and absence of neutralizing antibodies, leads to the development of fatal Lassa fever.[1]
Transmission
Rodent to Human
- Infection in humans typically occurs via exposure to animal excrement through the respiratory or gastrointestinal tracts.
- Inhalation of tiny particles of infective material (aerosol) is believed to be the most significant means of exposure.
- It is possible to acquire the infection through broken skin or mucous membranes that are directly exposed to infective material. In fatal cases, Lassa fever is characterized by impaired or delayed cellular immunity leading to fulminant viremia[2].
- Finally, because Mastomys rodents are sometimes consumed as a food source, infection may occur via direct contact when they are caught and prepared for food.
Human to Human
- There are a number of ways in which the virus may be transmitted, or spread, to humans.
- This type of transmission occurs when a person comes into contact with virus in the blood, tissue, secretions, or excretions of an individual infected with the Lassa virus.
- The virus cannot be spread through casual contact (including skin-to-skin contact without exchange of body fluids).
- Person-to-person transmission is common in both village and health care settings, where, along with the above-mentioned modes of transmission, the virus also may be spread in contaminated medical equipment, such as reused needles (this is called nosocomial transmission). Frequency of transmission via sexual contact has not been established. * Transmission through breast milk has also been observed.
Pathology
- Endothelial cell damage/ capillary leak.
- Platelet dysfunction.
- Supressed cardiac function.
- Cytokines and other cell mediators of shock and inflammation.
- Some of the characteristic symptoms of the virus include: fever, muscle aches, sore throat, nausea, vomiting, chest and abdominal pain, weakness, cough, headache, exudative pharyngitis, anemia, low blood pressure, and diarrhea. Because its symptoms are similar to other febrile illness found in Africa, Lassa virus is hard to diagnose. It can eventually can cause pulmonary edema, pleural and pericardial effusion, facial edema, bleeding from mucosal surfaces, neurological complications, deafness, lymphocytopenia, thrombocytopenia, and ascites. Often sore throat, vomiting, and bleeding are associated with higher fatality. Microscopically, the virus causes hepatocellular necrosis and capillary lesions that can cause certain organs to hemorrhage. Lassa virus travels through the body via the blood, lymph vessels, respiratory tract, and digestive tract. Because of the multitude of dissemination strategies in the body, it is able to infect almost every organ in the human body. It has even been found in the cerebrospinal fluid which suggests a malfunction or defect of the blood brain barrier. Even though the virus targets the entire body, the liver is usually the organ that is most affected. The virus escapes detection by suppressing the immune system. There are four clinical stages of Lassa fever. The first stages occurs within the first three days and its symptoms include a high fever, weakness, and a general depression in activity. The second stage transpires from day 4 to day 7 where the patient experiences some of the more common/characteristic symptoms as stated above. The third stage begins at the seventh day and includes more severe symptoms such as: facial edema, convulsions, mucosal bleeding, internal bleeding, and disorientation. The fourth stage usually occurs after the 14th day and ends in coma and death.
- Only 20% of people who contract Lassa fever have severe multisystem trauma, meaning that 80% of people have only the milder symptoms. It has also been found that most cases of Lassa fever occur as the seasons change from dry to wet.
- The Lassa virus is diagnosed several ways including the discovery of the viral antigen, antibodies, or virus culture. One way to detect the virus antigen is to use the virus’s antibodies in enzyme-linked immunosorbent assays (ELISAs). The virus can also be revealed though indirect immunoflourescence which detects the virus antibodies IgM and IgG. Lastly, the virus can be uncovered using reverse transcription PCR after first reverse transcribing the RNA of the virus into DNA.
- While, at present, there is no vaccine for Lassa virus, the broad-spectrum nucleoside analogue ribaviran has been demonstrated to have therapeutic effect on patients suffering from Lassa fever. Ribaviran works by mutating the progeny genomes of the virus by incorporating itself into the virus’s RNA. While this method has been proven to reduce mortality, it is most successful if it is given within 6-7 days of the start of symptoms. Ribaviran by itself is not enough, the patient also needs rigorous care in the hospital setting. Someone suffering from Lassa virus needs to have their fluids and electrolytes kept in balance, they require the proper amount of oxygen, their blood pressure needs to be monitored, and they need prompt treatment for any complications that may arise.
References
- ↑ Flatz L, Rieger T, Merkler D, Bergthaler A, Regen T, Schedensack M; et al. (2010). "T cell-dependence of Lassa fever pathogenesis". PLoS Pathog. 6 (3): e1000836. doi:10.1371/journal.ppat.1000836. PMC 2847900. PMID 20360949.
- ↑ 2.0 2.1 "wikipedia".