Virology

OVERVIEW OF VIRAL HAEMORRHAGIC FEVERS

Written by MicroDok

There is actually no consensus to the definition of viral haemorrhagic fevers. However, this section is aimed at letting the reader know the general concept regarding this dreaded disease of mankind. Viral haemorrhagic fevers are viral infections or diseases generally characterized by haemorrhage (bleeding) resulting from various forms of capillary damage of organs of the body. This type of viral disease is caused by a consortium of distinct viral groups generally known as viral haemorrhagic fevers of humans. And they include Ebola virus, Lassa virus, Marburg virus, Chikungunya virus and rift valley virus amongst others. It is noteworthy that the viruses responsible for causing viral haemorrhagic fevers in humans are mainly found in only four (4) viral families, they include: Flaviviridae family, Arenaviridae family, Filoviridae family and Bunyaviridae family.

Viral haemorrhagic fevers (VHFs) are also characterized by high fever aside other peculiar clinical symptoms and signs of each viral disease agent that cause VHF. Human infections with the causative agents of VHFs usually occur when humans venture into the ecological domain of the natural hosts of these viruses. Rodents, primates, chimpanzees and arthropods are the main natural hosts or reservoirs of viral haemorrhagic fever viruses of humans. VHF is a multisystem syndrome – because VHF affects several organs of the human body; and the disease leads to sporadic internal bleeding from the vascular systems and capillaries of the affected organs. Viral haemorrhagic fever viruses rarely cause mild viral infections; and most of the diseases caused by these pathogens are usually life-threatening and they also have very high mortality rate. The Ebola outbreak of 2014 in some parts of West Africa attests to the severity of infections caused by viral haemorrhagic fever viruses.

As aforementioned, viral haemorrhagic fever viruses are usually acquired when humans venture into the ecological niche of animals reservoirs of these viruses. Direct contact with an infected individual is one of the major routes of transmission of the disease within a defined human population. Inadequate infection control practices in healthcare facilities as well as contact with the body fluids of infected persons or cadavers of VHF victims are common routes of transmitting the disease between the hospital and community. The transmission of viral haemorrhagic fever in a healthcare setting is frequent amongst healthcare workers, and they also serve as medium through which the disease can spread from the hospital to the community.

The natural reservoirs or hosts of viral haemorrhagic fever viruses include bats, monkeys, chimpanzees, arthropods such as mosquitoes and primates. Viral haemorrhagic fever viruses can also spread from person to person via direct contact with body fluids of infected persons and also via contaminated hospital equipments or instruments including syringes and needles. Contaminated syringes and needles plays an important role in the transmission of viral haemorrhagic fever viruses especially in hospital settings where disease outbreak is likely to occur.

Humans are not the natural reservoirs of viral haemorrhagic fever viruses. Human infection with these pathogens only occurs when humans come into contact with infected humans hosts or any of the natural reservoirs of the disease agent. It is worthy of note that the viral haemorrhagic fever viruses that causes VHF in humans are all RNA-containing viruses (i.e. they are RNA viruses). And they are all enveloped viruses as well. Because the causative agents of VHF in humans are mainly reserved in animals, VHF can also be referred to as zoonotic viral infection or disease – since they are usually transmitted from animals to humans. The hosts of some viral haemorrhagic fever viruses such as Marburg virus and Ebola virus is still unknown even though they are believed to be transmitted to humans via primates, monkeys or chimpanzees as well as infected/contaminated bush meats. Most of the VHFs are geographically restricted to some regions of the world, and this has been used in the classification or naming of some of the viral agents that cause VHFs in humans. Some of the VHFs only occur in countries or regions of the world where the natural host of the virus seems to occur.

Most of the VHFs are named after the country, region or town where they first occurred. For example, Marburg haemorrhagic fever first occurred in Marburg and Frankfurt in Germany; and Lassa fever was named after the town in northern Nigeria where the first disease outbreak occurred in 1969. Contamination of the food of humans by the excreta or urine of rodents harbouring any of these viruses and the consumption of bush meats infected by the virus is also another common means via which human infection can occur. And for those viral haemorrhagic fevers whose natural hosts are arthropods (such as the yellow fever virus), human infections with such viruses usually occur following insect bite during blood meal. The clinical presentation of VHFs varies from one VHF to another. However, the commonest symptoms of VHF as aforementioned include bleeding and sudden onset of fever, myalgias, and prostration as well as general body weakness. VHF is a notifiable disease and must be reported to local health authorities who will take appropriate containment measures to stop the spread of the disease.

The use of PCR, antigen detection tests and virus isolation are the commonest means of diagnosing the disease, but clinical samples for VHF investigations are normally carried out in reference laboratories with suitable biosafety level 4 (BSL-4) equipments and facility for the management and processing of such highly infectious agents. Some VHF has no specific antiviral drug for treatment but Ribavirin is used for the effective treatment of Lassa fever and some Arenaviruses that cause VHF in humans. Early diagnosis and treatment is vital to avert death; and avoiding contact with the natural host or vectors in endemic countries is crucial to the prevention of VHF. Vaccines for the prevention or protection of susceptible human population against the contraction of viral haemorrhagic fever viruses does not exist except for yellow fever (caused by yellow fever virus transmitted via mosquito bite) for which a vaccine exist. However, vaccine development for some life-threatening viral haemorrhagic fevers such as Ebola is underway.

The best mode of preventing human infection with viral haemorrhagic fevers is avoiding contact with the natural hosts of the viruses that cause these deadly diseases. Safe cleanup of our environments especially by avoiding and discouraging rodents from entering our homes and defeacating on raw food materials is critical to the prevention of the spread of the disease. And proper rodent controls should also be instituted in regions where some viral haemorrhagic fevers are endemic. For viral haemorrhagic fever viruses transmitted via arthropods (e.g. yellow fever virus), the proper control of insect vectors that harbour these pathogens will help to preventing human infection with the disease agent. Proper infection control practices should be instituted in hospitals located in regions where these viral agents are endemic; and when disease outbreak due to any of these agents occur, prevention should be focused on avoiding human contacts with already infected people.

References

Acheson N.H (2011). Fundamentals of Molecular Virology. Second edition. John Wiley and Sons Limited, West Sussex, United Kingdom.

Alan J. Cann (2005). Principles of Molecular Virology. 4th edition. Elsevier Academic Press,   Burlington, MA, USA.

Alberts B, Bray D, Johnson A, Lewis J, Raff M, Roberts K and Walter P (1998). Essential Cell Biology: An Introduction to the Molecular Biology of the Cell. Third edition. Garland Publishing Inc., New York.

Balows A, Hausler W, Herrmann K.L, Isenberg H.D and Shadomy H.J (1991). Manual of clinical microbiology. 5th ed. American Society of Microbiology Press, USA.

Barrett   J.T (1998).  Microbiology and Immunology Concepts.  Philadelphia,   PA: Lippincott-Raven Publishers. USA.

Arthur R.R (2002). Ebola in African discoveries in the past decade. Euro Surveill, 7:33-36.

 

 

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MicroDok

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