Keeping up with Virus Taxonomy: Viruses that cause viral haemorrhagic fevers
Posted on May 15, 2023 by Clare Baker
In our last instalment of ‘Keeping up with Virus Taxonomy’ we explored the little-known viruses that infect fungi. For this new instalment we will explore some of the distinct virus families that many of you will have heard of; viruses that cause haemorrhagic fevers in humans.
According to the CDC ‘viral haemorrhagic fever’ (VHF) is a condition that affects multiple organ systems. Symptoms include haemorrhaging and can cause anything from a mild illness to a life-threatening disease. Most viral haemorrhagic fevers have no known cure or vaccine. Viruses that cause VHF belong to many different families of viruses but share similar characteristics; they are all RNA viruses; they are enveloped in a lipoprotein outer layer; they naturally exist in animal or insect host populations and are zoonotic diseases, transmitted to humans by an infected insect or animal host.
Arenaviridae
First up we have Arenaviridae. These viruses infect fish, snakes and mammals and are classified into four genera Antennavirus, Hartmanivirus, Mammarenavirus, and Reptarenavirus. Reptarenaviruses can infect captive snakes and cause boid inclusion body disease. Snakes infected with the disease show symptoms such as head tremors, muscle spasms and a lack of appetite1. Unfortunately, no treatment or cure for boid inclusion body disease is known and it is advised that snakes diagnosed with the disease should be euthanized. Another genus in the Arenaviridae family is Mamarenavirus, these viruses infect mammals and include Western African Lassa virus (LASV) which can cause haemorrhaging in the human host and is often fatal.
Filoviridae
This family of viruses contains of the most virulent viruses known to us. Ebola virus and Marburg virus find their home under the name, Filoviridae. Bats are natural hosts for some filoviruses, for example, Marburg Virus and it’s close relative, Ravn virus. Ebolavirus is an entire genus under the family of Filoviridae, and contains six species. The impact on humans varies from Tai Forest virus, which has only caused a single case of severe but non-lethal human disease to Ebola virus which has been responsible for multiple outbreaks with high fatality rates since it’s discovery in 1976 (CDC).
Flaviviridae
Most viruses in the Flaviviridae family infect mammals and birds. Like the rest of the viral haemorrhagic fevers, Flaviviridae are small and enveloped in a lipid outer layer. This is where the virus has an outer wrapping (called an envelope). Viruses which are enveloped are often more susceptible to disinfectants.
Many members of the Flaviviridae family are arthropod-borne, infecting mosquitos and ticks, and are important human and veterinary pathogens. You may have heard of the yellow fever virus, which belongs to this family.
Nairoviridae
Much like Flaviviridae, viruses in the family Nairoviridae are maintained in arthropods or transmitted by ticks. Most notably, Crimean-Congo hemorrhagic fever virus is a tick-borne virus that is endemic in much of Asia, Africa, Southern and Eastern Europe. This virus infects humans and causes severe and frequently fatal disease. Another significant nairovirus is Nairobi sheep disease virus, which is also transmitted by ticks, and causes lethal haemorrhagic gastroenteritis in small ruminants in Africa and India. Haemorrhagic gastroenteritis is characterised by bloody diarrhoea, vomiting and lack of appetite2.
The International Committee on Taxonomy of Viruses (ICTV) is responsible for developing and maintaining a universal virus taxonomy. Known viruses are categorised into a classification scheme taking into consideration their physical and biological properties in combination with their phylogenetic relationships.
These two-page summaries of each chapter of the ICTV Report (a free resource published by the ICTV which provides an up-to-date description of virus taxonomy) are freely available in the Journal of General Virology, and are supported by the Microbiology Society. These summaries are known as ICTV Virus Taxonomy Profiles and describe the structure, replication and taxonomy of each virus order and family.
References
2 https://www.medivet.co.uk/pet-care/pet-advice/haemorrhagic-gastroenteritis-hge/
