MfA - Viral Hemorrhagic Fever, VHF

Medicine for Africa - Medical Information Service

IRAL EMORRHAGIC EVER

Definition:

Viral hemorrhagic fever (VHF) is caused by a diverse four-member group of enveloped RNA viruses, causing human and animal illnesses. This group includes the following virus families:

Arenaviridiae – responsible for Lassa fever, and Argentine, Bolivian and Venezuelan hemorrhagic fevers;
Bunyaviridae – causative agents of the Hantavirus pulmonary syndrome (HPS), the hemorrhagic fever with renal syndromes (HFRS), the Crimean-Congo hemorrhagic fever (CCHF), and Rift Valley fever (RVF);
Filoviridae – including the fatal Ebola virus and Marburg virus;
Flaviviridae – causing dengue fever and yellow fever.

All viruses can cause a viral hemorrhagic fever (VHF) of various extent, which is generally characterized by fever and bleeding disorders, which can progress to a life-threatening disease, shock and death in severe cases (Ebola and Marburg viruses).

VHF describes a syndrome that affects multiple organs in the body – it characteristically damages the vascular system and the body’s own ability to regulate itself, often resulting in extravasation of red blood cells (RBCs) into organs and perivascular tissue (thus its name).

Arenaviridae – rodents are the main vector of transmission to humans. The Lassa virus in Africa is clinically the most significant arenavirus and associated with high morbidity and mortality rates. Lassa virus is usually transmitted via virus-containing droppings of small rodents.

Bunyaviridae – those causing RVF and CCHF are arthropod-borne viruses, transmitted via mosquitoes or ticks, respectively. RVF can also be transmitted when slaughtering infected livestock; CCHF causes a fulminant, highly pathogenic and infectious form of VHF which is also significant for its aerosol form of transmission. RVF and CCHF occur in Africa, the latter also in Europe and Asia.

Filoviridae – include the notorious Ebola and Marburg viruses. The natural host for both viruses is still unknown, they are both endemic to (mostly) Central Africa, and are usually associated with a high fatality rate.

Flaviviridae – are the causative agents of the well known, mosquito-borne dengue fever (in Africa, Asia and the Americas) and yellow fever (in tropical Africa and South America).

The natural reservoir of hemorrhagic fever (HF) causing viruses is an animal or insect host, such as rodents and arthropods, respectively. Rodent hosts include the cotton rat, the multimammate rat, as well as the deer mouse, the common house mouse and other field rodents. Ticks and mosquitoes are the arthropod hosts that serve as vectors for some of the VHF causing viruses.

Transmission of HF viruses from their hosts to humans usually occurs when humans have contact with urine, fecal matter, saliva or other bodily fluids from the infected rodent. Transmission of the viruses which require an arthropod host, are usually spread via the bite of a vector mosquito or tick, or even when a person crushes a tick (and gets in contact with the tick's blood).

Humans are not part of HF viruses’ natural reservoir, but can become infected if they come into contact with one of the infected hosts.

However, some of the HF viruses can also be transmitted from one (infected) person to another – these include in particular the Ebola, the Marburg, the Lassa and the CCHF viruses. This kind of transmission can occur through close contact with the infected person or the person’s blood, blood products, or other body fluids, such as urine or semen (thus it can also be transmitted sexually!). Contaminated syringes and needles have been involved in spreading Ebola hemorrhagic fever as well as Lassa fever.

Symptoms:

Specific signs and symptoms may vary among the different types of HF viruses; however, they usually include several of the following:

High fever, fatigue and dizziness;
Muscle aches, loss of strength and exhaustion;
Headaches, vomiting and diarrhea;
Flushing of the face and chest;
Bleeding = hemorrhagic occurrences:

Within or under the skin;
Into internal organs – gastrointestinal tract;
Frank bleeding from mouth, ears or even eyes (conjunctival hemorrhage);

Nondependent edema (especially Lassa virus);
Renal failure;
Hypotension;
Breathing problems;
Shock, coma, delirium and seizures.

Diagnosis:

Blood tests can reveal severe abnormalities, although none is specific for any VHF in particular. Leukopenia (low white blood cell count) and thrombocytopenia (low platelets) are present in all VHFs except Lassa fever. VHF is also associated with increased values of prothrombin time (PT), partial thromboplastin time (PTT), the international normalized ratio (INR), and clotting times – all being a result of the active bleeding process that occurs during the infection.

Elevated values of hepatic transaminases (liver enzymes) are often observed in VHF and, if present in Lassa fever, they can predict a high mortality rate of this infection.

Specific serologic tests for the presence of the virus in blood include ELISA (Enzyme linked Immuno-Sorbent Assay) and the polymerase chain reaction (PCR). However, both tests require well equipped laboratories and specifically trained technicians to perform these rather expensive tests. Cultures may also be necessary, especially in difficult to diagnose cases. Because of the highly infectious disease agents, handling of any blood or tissue samples has to be performed with the utmost care in order to prevent transmission to the health care personnel.

Therapy:

Effective medical treatment of VHF patients is limited to only some viruses. Antiviral treatment with intravenous ribavirin may be useful in infections caused by viruses of the Bunyaviridae and Arenaviridae families, specifically Lassa fever, Rift Valley fever (RVF), Crimean-Congo hemorrhagic fever (CCHF), and the hemorrhagic fever with renal syndrome (HFRS) caused by the Old World Hantavirus.

The mainstay of treatment for those and all other types of HF viruses consists of supportive therapy, such as IV fluids, electrolytes, proper nutrition and comforting care.

Convalescent-phase plasma from patients who survived a previous illness has been used experimentally with some success in patients with Argentine hemorrhagic fever.

Prevention:

Vaccines are only available against yellow fever and the Argentine hemorrhagic fever; there are no vaccines available against any other VHFs. Thus, prevention has to be concentrated on avoiding contact with the hosts, or on taking particular efforts to safeguard oneself when caring for an infected patient, such as family members or healthcare personnel. Thus, it is important to isolate infected patients in the hospital, in order to prevent the spread of VHF to other inpatients. Medical and other health care related personnel have to wear protective clothing, only use single-use syringes and needles, and properly disinfect and sterilize any instruments and devices that have come into contact with the patient.

Since many VHF hosts are rodents, prevention efforts should include the best possible control of the rodent population, especially preventing rodents from entering living spaces such as homes and workplaces. Also, community teaching should stress the safe approach and removal of rodent nests and droppings.

Prevention against arthropod transmitted viruses requires community-wide insect and arthropod control wherever possible. In addition, insect repellents, proper clothing and especially bednets and window screens can be relatively cheap, simple and effective barriers against virus carrying insects.

_________________________________________________________________________________
DISCLAIMER: The above article is only intended to provide general information regarding this topic. It is not intended and does NOT replace the need to consult a medical or other professional person, if you have or believe to have this disease/disorder. While the article was researched, written and reviewed by medical professionals, and Medicine for Africa, its staff and publisher made every effort to assure accuracy and correctness, it does not claim to be complete, correct or to reflect the very latest stand of medical/scientific knowledge in the disease’s/syndrome’s pathology, diagnostic and/or therapeutic development. Medicine for Africa, its founder, management, staff, writers, reviewers or publishers may NOT be made responsible or legally bound to any information provided above, and cannot be held liable to any conclusions or decisions the reader may draw after reading this article. The reader is explicitly advised to consult a licensed physician and to present his/her specific situation before making any health related decisions.