ARENAVIRIDAE FAMILY

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Arenaviridae family is comprised of viruses that are transmitted from animals particularly rodents such as mice, rabbits and rats to humans when they come in direct contact with the aerosolized excreta including urine, saliva and faeces of these animals. These rodents serve as the natural host or reservoirs of the viruses in the Arenaviridae family. Human infection with viruses in the Arenaviridae family occurs through contact with the excreta of these animals (for example, rats and rabbits). Generally, the viruses in this family cause serious disease in humans; and these infections are collectively known as haemorrhagic fevers because of the invariable bleeding from different body sites of infected humans. Filoviridae family, Bunyaviridae family and Flaviviridae family are other viral families aside the Arenaviridae family that contain viruses which cause haemorrhagic fevers in humans. Viruses in the Arenaviridae family have an ambisense genome; and this implies that their genetic makeup is partially coded as positive (+) sense and as negative sense (-) at the same time.

The phrase “ambisense” is generally used to describe viruses with a single-stranded RNA genome, and whose genetic coding sequences is also expressed in the positive sense (+) as well as in the negative sense (-). Arenaviruses (i.e., viruses found in the Arenaviridae family) are typical examples of viruses whose genomes are expressed in the ambisense configuration as ‘ss(+/-)’. Arenaviruses are enveloped viruses, and they possess an ssRNA genome that is ambisense in nature as aforementioned. Structurally, Arenaviruses have a helical nucleocapsid. Arenaviruses replicate in the cytoplasm of their host cell. Arenaviruses are released by a budding process through the cytoplasmic membrane of their host cell since they are enveloped viruses. They measure between 110-300 nm in diameter. Arenaviruses are sensitive to UV light, chlorine compounds, high temperatures and to other organic compounds.

Viruses in the Arenaviridae family are distributed worldwide, and they cause haemorrhagic fevers that are chronic in nature. Arenaviruses cause asymptomatic infections in rodents such as rats, mice and rabbits (which are the natural hosts of these viruses). However, humans show clinical signs of the disease and become symptomatic when they come in contact with the body fluids or excreta of the rodents harbouring the viral pathogen. Arenaviruses are basically divided into two genera: Old World Arenaviruses and New World Arenaviruses. Viruses in the Old World Arenavirus genera which cause infections in humans include Lassa virus (LASV) and Lymphocytic choriomeningitis virus (LCMV). Machupo virus (MACV), Junin virus (JUNV), Sabia virus (SABV) and Guanarito virus (GTOV) are examples of viruses in the New World Arenavirus genera that cause disease in humans.

The New World Arenavirus are geographically limited because they are mostly found in South American countries including Venezuela (e.g., GTOV), Argentina (e.g. JUNV), Bolivia (e.g., MACV) and Brazil (e.g. SABV) where they cause haemorrhagic fevers that are peculiar to each region. LASV cause haemorrhagic fever in countries in the African continent especially in West Africa including Nigeria. The causative agent (i.e., LASV) of the haemorrhagic fever caused by LASV infection in human population is naturally found in the rodent species known as Mastomys natalensis.Mastomys natalensis is a multimammate mouse that readily enters people’s houses especially in the rural areas where these rodents are also eaten as a delicacy. LCMV, the causative agent of aseptic meningitis is distributed worldwide; and the pathogen causes febrile illness and central nervous system disease occasionally.

Lymphocytic choriomeningitis virus (LCMV) is naturally found in the house mouse species known as Mus musculus, from which human infections occurs especially when people come in contact with the excreta or body fluids of the pathogen’s natural host (i.e., Mus musculus). Lassa virus (LASV), the causative agent of Lassa fever (a type of haemorrhagic fever) is endemically found in Africa particularly in West Africa where it was first discovered in a town known as Lassa in the Northern part of Nigeria in 1969 after it killed an American missionary nurse stationed at that location as at the time. The virus has caused a number of outbreaks in recent times in many regions of West Africa including Nigeria where periodic outbreak of Lassa fever normally occurs even in healthcare facilities and some rural and urban areas in Nigeria. The mortality rate of Lassa fever is high.

Arenaviruses including LASV are aerogenically introduced into the human body through contact with excreta or urine or body of rodents (in this case: Mastomys natalensis) that naturally harbour the virus. After invasion, affected individuals show symptomatic viraemia; and this is immediately followed by invasion and attack of various internal organs of the body. Clinical symptoms of haemorrhagic fever due to LASV infection include myalgia, fever, severe prostration, body pain or weakness and other haemorrhagic or neurological signs. This is also followed by severe gastrointestinal upset such as abdominal pain, nausea and vomiting, and diarrhea. Profuse bleeding from the nose, eyes, mouth and ears (which is usually rare and occurs in some cases of the disease) occurs in infected individuals. At this stage of bleeding the disease becomes fatal and may claim the life of the patient if proper treatment and medical care is not administered immediately.

The incubation period of LASV infection is between 10-21 days; and infected patients becomes symptomatic immediately after infection. The clinical management of patients infected with LASV is usually based on a supportive therapy that is geared toward stopping the bleeding and maintaining the normal functioning of affected vital organs of the body. However, the antiviral drug ribavirin has been used for treatment as well as for prophylaxis purposes especially in those who are exposed to the virus. LASV can be transmitted from an infected person to a susceptible or unexposed host; and human contact with excreta of rodents harbouring the virus as well as contact with body fluids of infected persons is the most common route of contamination or contraction of the viral pathogen. Consumption of food infected or contaminated with the excreta or urine of rodents that harbour the pathogen is also another major route through which human infection can occur.

LASV and other Arenaviruses form stable and infectious aerosols when shed through faeces, saliva or urine of the rodents. This account for the ease with which human infections occurs especially when humans come in contact with excreta from the multimammate mouse or other materials including food stuffs contaminated with the excreta or urine of the rodent. The prevention and control of haemorrhagic fever caused by Arenaviruses especially LASV that ravages some parts of West Africa is mainly based on effective rodent control measures since these pathogens are naturally harboured in these animals. Some human activities such as hunting, bush burning and deforestation also contribute in the displacement of these rodents from their natural habitat, thus bringing them in close contact with human population.

In most rural communities in West Africa, the rodents (which are the natural hosts or reservoirs of these viruses) are eaten as delicacies; and this could serve as route through which the disease can spread in a defined human population. People who eat rodents including rats in endemic regions are at high risk of contracting or becoming infected with LASV, the causative agent of Lassa fever. No vaccine currently exists for the prevention of haemorrhagic fever caused by LASV. The primary transmission of LASV is from its natural host i.e., multimammate mouse (M. natalensis) to humans who eat the animals and those who come in contact with the excreta, urine or aerosols of the rodents. Therefore, people who live in regions where the disease is endemic or where these natural hosts of Arenaviruses are common should avoid contact with them as much as possible.

Raw food stuffs should be properly stored and covered in containers so that the rats do not excrete on them. Healthcare practitioners and laboratory personnel should always wear the correct protective wears including laboratory/hospital gowns, eye masks or goggles and gloves when clerking patients and handling samples from potentially infected individuals because the Arenaviruses are highly infectious. 

Further reading

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

Brian W.J Mahy (2001). A Dictionary of Virology. Third edition. Academic Press, California, USA.

Cann A.J (2011). Principles of Molecular Virology. Fifth edition. Academic Press, San Diego, United States.

Carter J and Saunders V (2013). Virology: Principles and Applications. Second edition. Wiley-Blackwell, New Jersey, United States.

Dimmock N (2015). Introduction to Modern Virology. Seventh edition. Wiley-Blackwell, New Jersey, United States.

Kudesia G and Wreghitt T (2009). Clinical and Diagnostic Virology. Cambridge University Press, New York, USA. 

Marty A.M, Jahrling P.B and Geisbert T.W (2006). Viral hemorrhagic fevers. Clin Lab Med, 26(2):345–386.

Strauss J.H and Straus E.G (2008). Viruses and Human Diseases. 2nd edition. Elsevier Academic Press Publications, Oxford, UK.

Zuckerman A.J, Banatvala J.E, Schoub B.D, Grifiths P.D and Mortimer P (2009). Principles and Practice of Clinical Virology. Sixth edition. John Wiley and Sons Ltd Publication, UK.

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