Lecture #168: Microbiology: Hemorrhagic Viral Infections

What are the major viral families causing hemorrhagic fevers?

Arenaviridae, Bunyaviridae, Filoviridae, and Flaviviridae, all associated with vascular damage and hemorrhage.

What is the defining feature of viral hemorrhagic fevers (VHF)?

Severe multisystem disease with primary involvement of the vascular system leading to hemorrhage.

What are common structural features of VHF viruses?

Enveloped, single-stranded RNA viruses with animal reservoirs rather than humans.

Why are humans not natural reservoirs for VHF viruses?

These viruses persist in animals or environment and humans are incidental hosts.

What are common reservoirs for hemorrhagic viruses?

Rodents, mosquitoes, ticks, bats, and primates depending on the virus family.

What is the general pathophysiology of VHF?

Viral infection of endothelial and immune cells leading to vascular damage, leakage, and hemorrhage.

What are Arenaviruses characteristics?

Enveloped, segmented (-) ssRNA viruses transmitted from rodents.

How are Arenaviruses transmitted to humans?

Contact or inhalation of aerosolized rodent urine or feces, and occasionally person-to-person.

What cells do Arenaviruses infect?

Macrophages, triggering interferon release and vascular damage.

What is incubation period for Arenavirus infections?

Approximately 10–14 days.

What disease is caused by Lassa virus?

Lassa fever, a hemorrhagic illness endemic to West Africa.

What is the reservoir for Lassa virus?

Multimammate rat (Mastomys natalensis).

What are common symptoms of Lassa fever?

Fever, headache, sore throat, cough, abdominal pain, vomiting, and hemorrhage.

What severe complications occur in Lassa fever?

Organ failure, shock, and vascular collapse in severe cases.

What is a key complication of Lassa virus?

Hearing loss (deafness) in about one-third of patients.

How is Lassa virus diagnosed?

RT-PCR or ELISA testing.

What is treatment for Lassa fever?

Ribavirin and supportive care.

What are Bunyaviruses characteristics?

Enveloped, segmented (-) ssRNA viruses often transmitted by arthropods or rodents.

How are most Bunyaviruses transmitted?

Arthropod vectors such as mosquitoes, ticks, and flies.

How is Hantavirus transmitted?

Inhalation of aerosolized rodent urine, droppings, or saliva.

What disease does Hantavirus cause?

Hemorrhagic fever with renal syndrome.

What are early symptoms of Hantavirus infection?

Fever, chills, headache, nausea, abdominal pain, and back pain.

What severe complications occur in Hantavirus?

Hypotension, shock, vascular leakage, and acute renal failure.

What is treatment for Hantavirus?

Supportive care only.

What is prevention strategy for Hantavirus?

Rodent control and avoiding exposure to rodent excreta.

What are Flavivirus characteristics?

Enveloped, positive-sense ssRNA viruses transmitted by mosquitoes.

What is the vector for Dengue and Yellow Fever?

Aedes aegypti mosquito.

What is Dengue virus geographic distribution?

Southeast Asia, Western Pacific, Latin America, and Africa.

What are classic Dengue fever symptoms?

Fever, headache, rash, myalgia, arthralgia (“break-bone fever”), and retro-orbital pain.

What lab abnormality is common in Dengue?

Thrombocytopenia.

What is Dengue hemorrhagic fever?

A severe complication with bleeding, hepatomegaly, and possible circulatory failure.

When does bleeding occur in Dengue?

Typically 3–5 days after onset of fever.

What is unique about Dengue immunity?

Infection with one serotype provides immunity but increases risk of severe disease with others.

What is Dengue diagnosis?

RT-PCR or NAAT testing.

What is Dengue treatment?

Supportive care.

What is Yellow Fever transmission cycle?

Sylvatic (monkey to mosquito to human) and urban (human to mosquito to human).

What are key symptoms of Yellow Fever?

Fever, headache, back pain, vomiting, jaundice, and hemorrhage.

What is a hallmark pathology finding in Yellow Fever?

Councilman bodies (eosinophilic apoptotic hepatocytes).

How is Yellow Fever diagnosed?

ELISA, PCR, or liver biopsy.

What is Yellow Fever prevention?

Live attenuated vaccine.

Who should not receive Yellow Fever vaccine?

Infants <6 months, pregnant women, and immunocompromised individuals.

What are Filoviruses characteristics?

Enveloped, (-) ssRNA viruses infecting endothelial and immune cells.

What viruses belong to Filoviridae?

Ebola virus and Marburg virus.

What is the reservoir for Filoviruses?

Fruit bats and primates.

How are Ebola and Marburg transmitted?

Direct contact with infected blood, bodily fluids, or contaminated surfaces.

What is pathogenesis of Ebola/Marburg?

Cytokine storm, endothelial damage, tissue necrosis, leading to vascular leakage and DIC.

What are early symptoms of Ebola/Marburg?

Fever, fatigue, abdominal pain, vomiting, diarrhea, and myalgias.

What are late severe symptoms of Ebola/Marburg?

Delirium, hemorrhage, liver failure, DIC, and shock.

What is mortality rate of Ebola and Marburg?

Ebola 50–90%, Marburg ~25%.

How are Ebola and Marburg diagnosed?

RT-PCR testing.

What is treatment for Filovirus infections?

Primarily supportive care.

Why are Ebola and Marburg highly dangerous?

They cause rapid systemic damage, high mortality, and can trigger outbreaks.