The most detailed study on the frequency, onset, and duration of MVD clinical signs and symptoms was performed during the 1998–2000 mixed MARV/RAVV disease outbreak. A maculopapular rash, petechiae, purpura, ecchymoses, and hematomas (especially around needle injection sites) are typical hemorrhagic manifestations. However, contrary to popular belief, hemorrhage does not lead to hypovolemia and is not the cause of death (total blood loss is minimal except during labor). Instead, death occurs due to multiple organ dysfunction syndrome (MODS) due to fluid redistribution, hypotension, disseminated intravascular coagulation, and focal tissue necroses.

Clinical phases of Marburg Hemorrhagic Fever's presentation are described below. Note that phases overlap due to variability between cases.

1. Incubation: 2–21 days, averaging 5–9 days.

2. Generalization Phase: Day 1 up to Day 5 from onset of clinical symptoms. MHF presents with a high fever (~40˚C) and a sudden, severe headache, with accompanying chills, fatigue, nausea, vomiting, diarrhea, pharyngitis, maculopapular rash, abdominal pain, conjunctivitis, & malaise.

3. Early Organ Phase: Day 5 up to Day 13. Symptoms include prostration, dyspnea, edema, conjunctival injection, viral exanthema, and CNS symptoms, including encephalitis, confusion, delirium, apathy, and aggression. Hemorrhagic symptoms typically occur late and herald the end of the early organ phase, leading either to eventual recovery or worsening & death. Symptoms include bloody stools, ecchymoses, blood leakage from venipuncture sites, mucosal & visceral hemorrhaging, and possibly hematemesis.

4. Late Organ Phase: Day 13 up to Day 21+. Symptoms bifurcate into two constellations for survivors & fatal cases. Survivors will enter a convalescence phase, experiencing myalgia, fibromyalgia, hepatitis, asthenia, ocular symptoms, & psychosis. Fatal cases continue to deteriorate, experiencing continued fever, obtundation, coma, convulsions, diffuse coagulopathy, metabolic disturbances, shock and death, with death typically occurring between Days 8 and 16.

Marburg virus is a hemorrhagic fever virus of the "Filoviridae" family of viruses and a member of the species "Marburg marburgvirus", genus "Marburgvirus". Marburg virus (MARV) causes Marburg virus disease in humans and nonhuman primates, a form of viral hemorrhagic fever. Considered to be extremely dangerous, the WHO rates it as a Risk Group 4 Pathogen (requiring biosafety level 4-equivalent containment). In the United States, the NIH/National Institute of Allergy and Infectious Diseases ranks it as a Category A Priority Pathogen and the Centers for Disease Control and Prevention lists it as a Category A Bioterrorism Agent. It is also listed as a biological agent for export control by the Australia Group.

The virus can be transmitted by exposure to one species of fruit bats or it can be transmitted between people via body fluids through unprotected copulation and broken skin. The disease can cause bleeding (haemorrhage), fever and other symptoms much like Ebola. Funeral rituals are a particular risk. Actual treatment of the virus after infection is not possible but early, professional treatment of symptoms like dehydration considerably increase survival chances.

In 2009, expanded clinical trials of an Ebola and Marburg vaccine began in Kampala, Uganda.

The most common form of the disease is the head and eye form. Typical symptoms of this form include fever, depression, discharge from the eyes and nose, lesions of the buccal cavity and muzzle, swelling of the lymph nodes, opacity of the corneas leading to blindness, inappetance and diarrhea. Some animals have neurologic signs, such as ataxia, nystagmus, and head pressing. Peracute, alimentary and cutaneous clinical disease patterns have also been described. Death usually occurs within ten days. The mortality rate in symptomatic animals is 90 to 100 percent. Treatment is supportive only.

Marburg virus disease (MVD) is the official name listed in the World Health Organization's International Statistical Classification of Diseases and Related Health Problems 10 (ICD-10) for the human disease caused by any of the two marburgviruses Marburg virus (MARV) and Ravn virus (RAVV). In the scientific literature, Marburg hemorrhagic fever (MHF) is often used as an unofficial alternative name for the same disease. Both disease names are derived from the German city Marburg, where MARV was first discovered.

BVDV infection has a wide manifestation of clinical signs including fertility issues, milk drop, pyrexia, diarrhoea and fetal infection. Occasionally, a severe acute form of BVD may occur. These outbreaks are characterized by thrombocytopenia with high morbidity and mortality. However, clinical signs are frequently mild and infection insidious, recognised only by BVDV’s immunosuppressive effects perpetuating other circulating infectious diseases (particularly scours and pneumonias).

Bovine viral diarrhea (BVD) or bovine viral diarrhoea (UK English), and previously referred to as bovine virus diarrhoea (BVD), is a significant economic disease of cattle that is endemic in the majority of countries throughout the world. The causative agent, bovine viral diarrhea virus (BVDV), is a member of the "Pestivirus" genus of the family Flaviviridae.

BVD infection results in a wide variety of clinical signs, due to its immunosuppressive effects, as well as having a direct effect on respiratory disease and fertility. In addition, BVD infection of a susceptible dam during a certain period of gestation can result in the production of a persistently infected (PI) fetus.

PI animals recognise intra-cellular BVD viral particles as ‘self’ and shed virus in large quantities throughout life; they represent the cornerstone of the success of BVD as a disease.

Murray Valley encephalitis virus (MVEV) is a zoonotic flavivirus endemic to northern Australia and Papua New Guinea. It is the causal agent of Murray Valley encephalitis (previously known as Australian encephalitis or Australian X disease). In humans it can cause permanent neurological disease or death. MVEV is related to Kunjin virus which has a similar ecology but a lower morbidity rate. Although the arbovirus is endemic to Northern Australia, it has occasionally spread to the southern states during times of heavy rainfall during the summer monsoon season via seasonal flooding of the Murray-Darling river system. These outbreaks can be "...decades apart, with no or very few cases identified in between".

West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family Flaviviridae, specifically from the genus Flavivirus which also contain the Zika virus, dengue virus, and the yellow fever virus. The West Nile virus is primarily transmitted through mosquitoes, mostly by the Culex species. However, ticks have been found to carry the virus. The primary hosts of WNV are birds, so that the virus remains within a "bird-mosquito-bird" transmission cycle.

A viral disease (or viral infection) occurs when an organism's body is invaded by pathogenic viruses, and infectious virus particles (virions)

attach to and enter susceptible cells.

Viral disease is usually detected by clinical presentation, for instance severe muscle and joint pains preceding fever, or skin rash and swollen lymph glands.

Laboratory investigation is not directly effective in detecting viral infections, because they do not themselves increase the white blood cell count. Laboratory investigation may be useful in diagnosing associated bacterial infections, however.

Viral infections are commonly of limited duration, so treatment usually consists in reducing the symptoms; antipyretic and analgesic drugs are commonly prescribed.

Bovine malignant catarrhal fever (BMCF) is a fatal lymphoproliferative disease caused by a group of ruminant gamma herpes viruses including Alcelaphine gammaherpesvirus 1 (AlHV-1) and Ovine gammaherpesvirus 2 (OvHV-2) These viruses cause unapparent infection in their reservoir hosts (sheep with OvHV-2 and wildebeest with AlHV-1), but are usually fatal in cattle and other ungulates such as deer, antelope, and buffalo.

BMCF is an important disease where reservoir and susceptible animals mix. There is a particular problem with Bali cattle in Indonesia, bison in the US and in pastoralist herds in Eastern and Southern Africa.

Disease outbreaks in cattle are usually sporadic although infection of up to 40% of a herd has been reported. The reasons for this are unknown. Some species appear to be particularly susceptible, for example Pére Davids deer, Bali cattle and bison, with many deer dying within 48 hours of the appearance of the first symptoms and bison within three days. In contrast, post infection cattle will usually survive a week or more.

An emerging infectious disease (EID) is an infectious disease whose incidence has increased in the past 20 years and could increase in the near future. Emerging infections account for at least 12% of all human pathogens. EIDs are caused by newly identified species or strains (e.g. Severe acute respiratory syndrome, HIV/AIDS) that may have evolved from a known infection (e.g. influenza) or spread to a new population (e.g. West Nile fever) or to an area undergoing ecologic transformation (e.g. Lyme disease), or be "reemerging" infections, like drug resistant tuberculosis. Nosocomial (hospital-acquired) infections, such as methicillin-resistant Staphylococcus aureus are emerging in hospitals, and extremely problematic in that they are resistant to many antibiotics. Of growing concern are adverse synergistic interactions between emerging diseases and other infectious and non-infectious conditions leading to the development of novel syndemics. Many emerging diseases are zoonotic - an animal reservoir incubates the organism, with only occasional transmission into human populations.

Borna disease is an infectious neurological syndrome of warm-blooded animals, caused by Borna disease viruses 1 and 2 (BoDV-1/2), both of which are members of the species "Mammalian 1 bornavirus". BoDV-1 an 2 cause abnormal behaviour and fatality. Borna disease viruses 1 and 2 are neurotropic viruses and members of the "Bornaviridae" family within the "Mononegavirales" order.

Although Borna disease viruses 1 and 2 are mainly seen as the causative agent of Borna disease in horses and other animals, they are also controversially discussed as human infectious agents and therefore as potential zoonotic agents. The role of BoDV-1 and -2 in human illness is controversial and it is yet to be established whether BoDV-1 or -2 cause any overt disease in humans. However, correlative evidence exists linking BoDV-1/2 infection with neuropsychiatric disorders such as bipolar disorder.

In 80% of cases, the disease is asymptomatic, but in the remaining 20%, it takes a complicated course. The virus is estimated to be responsible for about 5,000 deaths annually. The fever accounts for up to one-third of deaths in hospitals within the affected regions and 10 to 16% of total cases.

After an incubation period of six to 21 days, an acute illness with multiorgan involvement develops. Nonspecific symptoms include fever, facial swelling, and muscle fatigue, as well as conjunctivitis and mucosal bleeding. The other symptoms arising from the affected organs are:

- Gastrointestinal tract

- Nausea

- Vomiting (bloody)

- Diarrhea (bloody)

- Stomach ache

- Constipation

- Dysphagia (difficulty swallowing)

- Hepatitis

- Cardiovascular system

- Pericarditis

- Hypertension

- Hypotension

- Tachycardia (abnormally high heart rate)

- Respiratory tract

- Cough

- Chest pain

- Dyspnoea

- Pharyngitis

- Pleuritis

- Nervous system

- Encephalitis

- Meningitis

- Unilateral or bilateral hearing deficit

- Seizures

Clinically, Lassa fever infections are difficult to distinguish from other viral hemorrhagic fevers such as Ebola and Marburg, and from more common febrile illnesses such as malaria.

The virus is excreted in urine for 3–9 weeks and in semen for three months.

The mode of transmission of BoDV-1/2 is unclear but probably occurs through intranasal exposure to contaminated saliva or nasal secretions. Following infection, individuals may develop Borna disease, or may remain subclinical, possibly acting as a carrier of the virus.

Reports from the 1980s and 1990s suggested RRV infection was associated with arthralgia, fatigue and depression lasting for years. More recent prospective studies have reported a steady improvement in symptoms over the first few months, with 15–66% of patients having ongoing arthralgia at 3 months. Arthralgias have resolved in the majority by 5–7 months. The incidence of chronic fatigue is 12% at 6 months and 9% at 12 months, similar to Epstein-Barr virus and Q fever. The only significant predictor of the likelihood of developing chronic symptoms is the severity of the acute illness itself. No other aspects of the patient's medical or psychiatric history have been found to be predictive. However, in those with the most persisting symptoms (12 months or more), comorbid rheumatologic conditions and/or depression are frequently observed .

Monkeypox is an infectious disease caused by the monkeypox virus. Symptoms begin with fever, headache, muscle pains, swollen lymph nodes, and feeling tired. This is then followed by a rash that forms blisters and crusts over. The time from exposure to onset of symptoms is around 10 days. The duration of symptoms is typically 2 to 5 weeks.

Monkeypox may be spread from handling bush meat, an animal bite or scratch, body fluids, contaminated objects, or close contact with an infected person. The virus is believed to normally circulate among certain rodents in Africa. Diagnosis can be confirmed by testing a lesion for the viruses DNA. The disease can appear similar to chickenpox.

The smallpox vaccine is believed to prevent infection. Cidofovir may be useful as treatment. The risk of death in those infected is up to 10%.

The disease mostly occurs in Central and West Africa. It was first identified in 1958 among laboratory monkeys. The first cases in humans were found in 1970 in the Democratic Republic of the Congo. An outbreak that occurred in the United States in 2003 was traced to a pet store where imported Gambian rodents were sold.

Brazilian hemorrhagic fever (BzHF) is an infectious disease caused by the Sabiá virus, an Arenavirus. The Sabiá virus is one of the arenoviruses from South America to cause hemorrhagic fever. It shares a common progenitor with the Junin virus, Machupo virus, Tacaribe virus, and Guanarito virus. It is an enveloped RNA virus and is highly infectious and lethal. Very little is known about this disease, but it is thought to be transmitted by the excreta of rodents.

There have only been three documented infections of the Sabiá virus, only one of which occurred naturally and the other two cases occurred in the clinical setting. The only naturally occurring case was in 1990, when a female agricultural engineer who was staying in the neighborhood of Jardim Sabiá near São Paulo, Brazil contracted the disease. She presented with hemorrhagic fever and died. Her autopsy showed liver necrosis. A virologist who was studying the woman's disease contracted the virus but survived. Ribavirin was not given in these first two cases. Four years later, in 1994, a researcher was exposed to the virus in a level 3 biohazard facility at Yale University when a centrifuge bottle cracked, leaked, and released aerosolized virus particle. He was successfully treated with ribavirin.

Ribavirin is thought to be effective in treating the illness, similar to other arenaviruses. Compared to the patients who did not receive ribavirin, the patient who was treated with it had a shorter and less severe clinical course. Symptomatic control such as fluids to address dehydration and bleeding may also be required.

The Sabiá virus is a Biosafety Level 4 pathogen.

This virus has also been implicated as a means for bioterrorism, as it can be spread through aerosols.

About 95% of symptomatic cases report joint pain. This is typically symmetrical and with acute onset, affecting the fingers, toes, ankles, wrists, back, knees and elbows. Fatigue occurs in 90% and fever, myalgia and headache occur in 50–60%.

A rash occurs in 50% of patients and is widespread and maculopapular. Lymphadenopathy occurs commonly; sore throat and coryza less frequently. Diarrhea is rare. About 50% of people report needing time off work with the acute illness. If the rash is unnoticed, these symptoms are quite easily mistaken for more common illnesses like influenza or the common cold. Recovery from the flu symptoms is expected within a month, but, because the virus currently cannot be removed once infection has occurred secondary symptoms of joint and muscle inflammation, pain and stiffness can last for many years.

Less common manifestations include splenomegaly, hematuria and glomerulonephritis. Headache, neck stiffness, and photophobia may occur. There have been three case reports suggesting meningitis or encephalitis.

MVEV is a mosquito-borne virus that is maintained in a bird-mosquito-bird cycle. Water birds from the order Ciconiiformes, including herons and cormorants, provide the natural reservoir for MVEV. The major mosquito vector is "Culex annulirostris". Human infection occurs only through bites from infected mosquitoes; the virus cannot be transmitted from person to person.

Epstein–Barr can cause infectious mononucleosis, also known as 'glandular fever', 'mono' and 'Pfeiffer's disease'. Infectious mononucleosis is caused when a person is first exposed to the virus during or after adolescence. It is predominantly found in the developing world, and most children in the developing world are found to have already been infected by around 18 months of age. Infection of children can occur when adults mouth feed or pre-chew food before giving it to the child. EBV antibody tests turn up almost universally positive. In the United States roughly half of five-year-olds have been infected.

In virology, defective interfering particles (DIPs), also known as defective interfering viruses, are spontaneously generated virus mutants in which a critical portion of the particle's genome has been lost due to defective replication. DIPs are derived from and associated with their parent virus, and particles are classed as DIPs if they are rendered non-infectious due to at least one essential gene of the virus being lost or severely damaged as a result of the defection. A DIP can usually still penetrate host cells, but requires another fully functional virus particle (the 'helper' virus) to co-infect a cell with it, in order to provide the lost factors. The existence of DIPs has been known about for decades, and they can occur within nearly every class of both DNA and RNA viruses.

The strongest evidence linking EBV and cancer formation is found in Burkitt's lymphoma

and nasopharyngeal carcinoma. Additionally, it has been postulated to be a trigger for a subset of chronic fatigue syndrome patients as well as multiple sclerosis and other autoimmune diseases.

Burkitt's lymphoma is a type of Non-Hodgkin's lymphoma and is most common in equatorial Africa and is co-existent with the presence of malaria. Malaria infection causes reduced immune surveillance of B cells immortalized by EBV, resulting in an excessive number of B cells and an increased likelihood of an unchecked mutation. Repeated mutations can lead to loss of cell-cycle control, causing excessive proliferation observed as Burkitt's lymphoma. Burkitt's lymphoma commonly affects the jaw bone, forming a huge tumor mass. It responds quickly to chemotherapy treatment, namely cyclophosphamide, but recurrence is common.

Other B cell lymphomas arise in immunocompromised patients such as those with AIDS or who have undergone organ transplantation with associated immunosuppression (Post-Transplant Lymphoproliferative Disorder (PTLPD)). Smooth muscle tumors are also associated with the virus in malignant patients.

Nasopharyngeal carcinoma is a cancer found in the upper respiratory tract, most commonly in the nasopharynx, and is linked to the EBV virus. It is found predominantly in Southern China and Africa, due to both genetic and environmental factors. It is much more common in people of Chinese ancestry (genetic), but is also linked to the Chinese diet of a high amount of smoked fish, which contain nitrosamines, well known carcinogens (environmental).

In the acute form of the disease caused by highly virulent strains, pigs may develop a high fever, but show no other noticeable symptoms for the first few days. They then gradually lose their appetites and become depressed. In white-skinned pigs, the extremities turn blueish-purple and hemorrhages become apparent on the ears and abdomen. Groups of infected pigs lie huddled together shivering, breathing abnormally, and sometimes coughing. If forced to stand, they appear unsteady on their legs. Within a few days of infection, they enter a comatose state and then die. In pregnant sows, spontaneous abortions occur. In milder infections, affected pigs lose weight, becoming thin, and develop signs of pneumonia, skin ulcers, and swollen joints.

Monkeypox is similar to smallpox, although it is often milder.

Limited person-to-person spread of infection has been reported in disease-endemic areas in Africa. Case-fatality ratios in Africa have ranged from 1% to 10%.