Viral Hemorrhagic Fevers

Transcription

1 Viral Hemorrhagic Fevers (VHFs)

2 Definition Viral hemorrhagic fevers (VHFs) refer to a group of illnesses that are caused by 4 distinct families of viruses. Characteristically, the overall vascular system is damaged, and the body's ability to regulate itself is impaired. These symptoms are often accompanied by hemorrhage; the bleeding, however, is itself rarely lifethreatening. While some types of hemorrhagic fever viruses can cause relatively mild illnesses, many of these viruses can cause severe, life-threatening disease.

3 Classification Viral hemorrhagic fevers (VHFs) are caused by viruses from four families: Arenaviruses Bunyaviruses Filoviruses Flaviviruses et.pdf

4 Similar Characteristics Each of these families share some characteristics: All are RNA viruses, and all are enveloped in a fatty (lipid) coating Their survival is dependent on an animal or insect host, called the natural reservoir The viruses are geographically restricted to the areas where their host species live Humans are not the natural reservoir for any of these viruses Humans become infected when they come into contact with infected hosts. However, with some viruses, after the accidental transmission from the host, humans can transmit the virus to one another Human cases or outbreaks of hemorrhagic fevers caused by these viruses occur sporadically and irregularly The occurrence of outbreaks cannot be easily predicted With a few noteworthy exceptions, there is no cure or established drug treatment for VHFs

5 Symptoms of VHF Specific signs and symptoms vary by the type of VHF, but initial signs and symptoms often include marked fever, fatigue, dizziness, muscle aches, loss of strength, and exhaustion. Patients with severe cases of VHF often show signs of bleeding under the skin, in internal organs, or from body orifices like the mouth, eyes, or ears. However, although they may bleed from many sites around the body, patients rarely die because of blood loss. Severely ill patient cases may also show shock, nervous system malfunction, coma, delirium, and seizures. Some types of VHF are associated with renal (kidney) failure.

6 Reservoir Hosts v. Arthropod Vectors Viruses associated with most VHFs are zoonotic, meaning that these viruses naturally reside in an animal reservoir host or arthropod vector. They are totally dependent on their hosts for replication and overall survival.

7 Definitions A reservoir host is: a nonhuman host that serves as a means of sustaining an infectious organism as a potential source of human infection. A vector is: a carrier, usually an arthropod, that transfers an infective agent from one host to another

8 Reservoir Hosts The multimammate rat, cotton rat, deer mouse, house mouse, and other field rodents are examples of reservoir hosts

9 Arthropod Vectors Ticks and mosquitoes serve as arthropod vectors for some of the illnesses. quito.jpg

10 ? The hosts of some viruses are still unknown Ebola and Marburg viruses are well-known examples

11 Fruit Bat

12 Arenaviridae This viral family includes: Argentine hemorrhagic fever Bolivian hemorrhagic fever Brazilian hemorrhagic fever Lassa fever * Venezuelan hemorrhagic fever

13 Lassa Fever Lassa fever is an acute viral illness that occurs in West Africa. The illness was discovered in 1969 when two missionary nurses died in Nigeria, West Africa. The cause of the illness was found to be Lassa virus, named after the town in Nigeria where the first cases originated. imgrefurl= MZJVSF8AKEM- RVhKQ0LcVb5Um0Y=&h=122&w=111&sz=6&hl=en&start=49&um=1&tbnid=GXXzISANb0ekHM:&tbnh=89&tbnw= 81&prev=/images%3Fq%3Dlassa%2Bfever%26ndsp%3D20%26hl%3Den%26rls%3Dcom.microsoft:en- US%26sa%3DN%26start%3D40%26um%3D1

14 Symptoms Fever, which may be constant or intermittent Pain behind your chest wall and in your back A sore and inflamed throat with white patches on your tonsils Cough Abdominal pain Vomiting Diarrhea Conjunctivitis (an inflammation of the transparent membrane (conjunctiva) that covers your eyelids and part of your eyeballs ) Bleeding from your gums or in your stomach, small intestine and other internal organs Facial swelling Temporary or permanent hearing loss Pleural effusion (fluid around your lungs) Encephalitis

15 Bunyaviridae This viral family includes: Crimean-Congo hemorrhagic fever Hantavirus pulmonary syndrome Hemorrhagic fever with renal syndrome Rift Valley fever *

16 Rift Valley Fever Rift Valley fever (RVF) is an acute, fever-causing viral disease that affects domestic animals (such as cattle, buffalo, sheep, goats, and camels) and humans. RVF is most commonly associated with mosquito-borne epidemics during years of unusually heavy rainfall.

17 Symptoms Fever Severe muscle aches Sore throat Headache Cough Diarrhea Encephalitis In the case of Crimean-Congo hemorrhagic fever, sore eyes and sensitivity to light (photophobia); mood swings and agitation; bleeding into the skin and from the gums, rectum and kidneys; and eventual pulmonary failure In the case of hantavirus pulmonary syndrome, shortness of breath and difficulty breathing, possibly leading to respiratory failure

18 Filoviridae This viral family includes: Ebola virus * Marburg virus *which are among the most virulent of all known diseases.

19 Ebola The disease is caused by infection with Ebola virus, named after a river in the Democratic Republic of the Congo (formerly Zaire) in Africa, where it was first recognized. There are five identified subtypes of Ebola virus. Four of the five have caused disease in humans: Ebola-Zaire, Ebola-Sudan, Ebola-Ivory Coast and Ebola- Bundibugyo. The fifth, Ebola-Reston, has caused disease in nonhuman primates, but not in humans.

20 Symptoms A distinctive, hemorrhagic rash, often appearing around the fifth day Bleeding from the nose, mouth, eyes, ears and rectum Seizures Coma Delirium Depending on the strain, Ebola and Marburg viruses are fatal in 50 to 90 percent of infected people and are almost always fatal in pregnant women.

21 Hemorrhagic Rash HLRyGfC607SBeoi4xO J3Tkq4lts=&h=320&w=400&sz=24&hl=en&start=4&um=1&tbnid=bGLWyk3_Qtm0jM:& tbnh=99&tbnw=124&prev=/images%3fq%3d%2522hemorrhagic%2brash%2522%26hl %3Den%26rls%3Dcom.microsoft:en-US%26um%3D1

22 Flaviviridae This viral family includes: Dengue fever Dengue hemorrhagic fever Kyasanur Forest disease Omsk hemorrhagic fever * Yellow fever

23 Omsk Fever Omsk hemorrhagic fever (OHF) is caused by Omsk hemorrhagic fever virus (OHFV), a member of the virus family Flaviviridae. OHF was described between 1945 and 1947 in Omsk, Russia from patients with hemorrhagic fever.

24 Omsk, Russia

25 Symptoms Fever, which may be constant or intermittent Headache Pain behind your eyes Pain in your arms and legs A rash on the soft palate of your mouth Swollen glands in your neck Diarrhea Vomiting Bleeding in your eyes Nosebleeds Bleeding in your gastrointestinal tract

26 Treatment Patients receive supportive therapy, but generally speaking, there is no other treatment or established cure for VHFs. Ribavirin, an anti-viral drug, has been effective in treating some individuals with Lassa fever or HFRS.

27 What needs to be done to address the threat of viral hemorrhagic fevers? Scientists and researchers are challenged with developing containment, treatment, and vaccine strategies for these diseases. Another goal is to develop immunologic and molecular tools for more rapid disease diagnosis, and to study how the viruses are transmitted and exactly how the disease affects the body (pathogenesis). A third goal is to understand the ecology of these viruses and their hosts in order to offer preventive public health advice for avoiding infection.