Virology

ARENAVIRIDAE FAMILY

Written by MicroDok

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 feaces of these animals. These rodents serve as the natural host or reservoirs of the viruses in the Arenaviridae family; and human infection occurs via contact with the excreta of these animals. 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 ambisenseis generally used to describe viruses with a single-stranded RNA genome, and whose genetic coding sequences is 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. They have a helical nucleocapsid; and 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 containing the 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; and these viruses are geographically limited because they are mostly found in South American countries including Venezuela (GTOV), Argentina (JUNV), Bolivia (MACV) and Brazil (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; and the causative agent of this disease is naturally found in the rodent species known as Mastomys natalensis, a multimammate mouse that readily enter 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. 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. The mortality rate of Lassa fever is high. Arenaviruses including LASV are aerogenically introduced into the human body via contact with excreta of rodents (in this case: Mastomys natalensis rats for LASV) 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; and at this stage of bleeding the disease becomes fatal and may claim the life of the patient. 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 is the most common route of contamination or contraction of the pathogen. Consumption of food infected or contaminated with the excreta of rodents that harbour the pathogen is also another route via which human infection can occur. LASV and other Arenaviruses form stable and infectious aerosols when shed via feaces, saliva or urine of the rodents; and 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. 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.

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 via which the disease can spread in a defined human population. 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 or aerosols contaminated with the excreta of the rodents. Thus 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’s 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.

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