Viruses are obligate intracellular parasites and the largest virus being visible only in the electron microscope. However, they are very much important from public health point of view. Several serious diseases including AIDS, polio, hepatitis A&B, yellow fever and viruses caused dengue. Some drugs exist against viruses, but the vaccines are most effective

Viral Hemorrhagic Fevers (VHFs) are caused by 4 families of virus and refer to a group of illnesses. Each family shows some common features. For example, a fatty covered them coatings and RNA viruses. They depend on animal host, called the natural reservoir for survival and geographically restricted to the host inhabiting areas. Generally VHFs are severe syndrome in which multiple organ systems are affected; especially the vascular system, often accompanied with bleeding, although the bleeding is rarely life-threatening.

The Special Pathogens Branch (classified hemorrhagic fever viruses as bio-safety level four (BSL-4) pathogens.

Human is not the natural reservoir but get infected in contact with infected hosts. Infected human can transmit the virus to other. VHF outbreaks occur sporadically, irregularly, and unpredictable. There is no cure or established drug for VHFs.
Viruses causing VHFs are zoonotic i.e. they naturally found in reservoir, or vector and are found over much of the globe. The rat, mouse, and other rodents are reservoirs. Ticks and mosquitoes are vectoring some VHFs. Rodents carrying viruses of Hantavirus Pulmonary Syndrome (HPS) are found in North and South America. Rodents carrying viruses for Hemorrhagic Fever with Renal Syndrome (HFRS) are found in Europe and Asia. Hosts like common rat, are distributed nearly worldwide, carry Seoul virus, a cause of HFRS and therefore, humans can get HFRS from areas where the common rat is found.

Occasionally people become infected by exotic animals. The first outbreaks of Marburg hemorrhagic fever in Marburg and Frankfurt, Germany and in Yugoslavia was reported, during handling of imported monkeys by laboratory workers. Viruses causing VHFs are initially transmitted to humans when the activities of infected reservoirs, or vectors and humans overlap. Humans get infected in contact with urine, fecal matter, saliva, or other body excretions from infected rodents. The viruses are spread with the bite of the vector mosquito or tick or when a human crushes a tick. Some vectors may spread virus to animals. Humans get infected when they care for slaughter the animals.

Hemorrhagic fever viruses can spread from one person to another, once an initial person has become infected are examples. Such transmission occurs directly through close contact with infected people or their body fluids or indirectly through contact with objects contaminated with infected body fluids. Contaminate syringes and needles play an important role in spreading infection.
Specific signs and symptoms vary depending on the type of VHF, but initial signs and symptoms include fever, fatigue, dizziness, muscle aches, and exhaustion. In severe cases Patients show signs of bleeding under the skin, in internal organs, or from the mouth, eyes, or ears. However, patients rarely die because of blood loss. Severely ill patient shows shock, nervous system malfunction, coma, delirium, and seizures. Some VHFs are associated with renal (kidney) failure.

Vaccines have been developed for yellow fever and Argentine hemorrhagic fever. No vaccines exist for other VHF’s. Avoiding close physical contact with infected people and their body fluids; isolating infected individuals and wearing protective clothing, proper use; disinfection, and disposal of instruments and equipment used in treating or caring for patients with VHF are suggested preventive measures .Insect and arthropod control by using insect repellant, bed nets, window screens, and other insect barriers are suggested avoiding insect bite. Disease prevention includes controlling rodent populations; preventing rodents from entering homes or workplaces and safe cleanup of rodent nests and droppings.

Vaccines are required to be developed urgently for these diseases. Understanding the ecology of these viruses and their hosts is also important to offer preventive public health advice for avoiding infection.

The author acknowledges the National Center for Infectious Diseases ,Centers for Disease Control and Prevention , USA as a source of information for this article.

This is an educational short film representing the syptoms, treatment, and prevention of the Yellow Fever virus.
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