Paravaccinia virus presents itself with blisters, nodules, or lesions about 4 mm in diameter, typically in the area that has made contact with livestock that is infected with bovine papular stomatitis. Lesions may begin forming as late as three weeks after contact has been made with an infected animal. In rare cases, lesions may be seen systemic. General signs of infection are also common, such as fever and fatigue.

Infected livestock may present with blisters or lesions on their udders or snout. Often, however, infected livestock show little to no symptoms.

Pathogenesis occurs in the same manner in hamsters as in mice. Symptoms in hamsters are highly variable, and typically indicate that the pet has been infected and shedding the virus for several months. Early signs may include inactivity, loss of appetite, and a rough coat. As the disease progresses, the animal may experience weight loss, hunched posture, inflammation around the eyes, and eventually death. Alternatively, some infected hamsters may be asymptomatic.

The BK virus rarely causes disease but is typically associated with patients who have had a kidney transplant; many people who are infected with this virus are asymptomatic. If symptoms do appear, they tend to be mild: respiratory infection or fever. These are known as primary BK infections.

The virus then disseminates to the kidneys and urinary tract where it persists for the life of the individual. It is thought that up to 80% of the population contains a latent form of this virus, which remains latent until the body undergoes some form of immunosuppression. Typically, this is in the setting of kidney transplantation or multi-organ transplantation. Presentation in these immunocompromised individuals is much more severe. Clinical manifestations include renal dysfunction (seen by a progressive rise in serum creatinine), and an abnormal urinalysis revealing renal tubular cells and inflammatory cells.

Paravaccinia virus is a viral infection of the Parapoxvirus genus of viruses. Human can contract the virus from contact with livestock infected with Bovine papular stomatitis and is common with ranchers, milkers, and veterinarians. Infection will present with fever, fatigue, and lesion on the skin.

LCMV causes callitrichid hepatitis in New World primates. The onset of the infection is nonspecific and may include fever, anorexia, dyspnea, weakness and lethargy. Jaundice is characteristic and petechial hemorrhages may develop. Prostration and death usually follow.

Necropsy lesions in primates with callitrichid hepatitis show signs of jaundice, hepatomegaly, splenomegaly, and subcutaneous and intramuscular hemorrhages. Pleural and pericardial effusion, sometimes sanguineous, has also been reported. On histology, multifocal necrosis with acidophilic bodies and mild inflammatory infiltrates are typically found in the liver.

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 signs shown depend on the horse's age, the strain of the infecting virus, the condition of the horse and the route by which it was infected. Most horses with EVA infection don't show any signs; if a horse does show symptoms, these can vary greatly in severity. Following infection, the first sign is fever, peaking at , followed by various signs such as depression, nasal discharge, "pink eye" (conjunctivitis), swelling over the eye (supraorbital edema), urticaria, and swelling of the limbs and under the belly (the ventral abdomen) which may extend to the udder in mares or the scrotum of male horses. More unusual signs include abortion in pregnant mares, and, most likely in foals, severe respiratory distress and death.

The BK virus was first isolated in 1971 from the urine of a renal transplant patient, initials B.K. The BK virus is similar to another virus called the JC virus (JCV), since their genomes share 75% sequence similarity. Both of these viruses can be identified and differentiated from each other by carrying out serological tests using specific antibodies or by using a PCR based genotyping approach.

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.

Viral entry is the earliest stage of infection in the viral life cycle, as the virus comes into contact with the host cell and introduces viral material into the cell. The major steps involved in viral entry are shown below. Despite the variation among viruses, there are several shared generalities concerning viral entry.

The incubation period for WNV—the amount of time from infection to symptom onset—is typically from between 2 and 15 days. Headache can be a prominent symptom of WNV fever, meningitis, encephalitis, meningoencephalitis, and it may or may not be present in poliomyelitis-like syndrome. Thus, headache is not a useful indicator of neuroinvasive disease.

- West Nile fever (WNF), which occurs in 20 percent of cases, is a febrile syndrome that causes flu-like symptoms. Most characterizations of WNF generally describe it as a mild, acute syndrome lasting 3 to 6 days after symptom onset. Systematic follow-up studies of patients with WNF have not been done, so this information is largely anecdotal. In addition to a high fever, headache, chills, excessive sweating, weakness, fatigue, swollen lymph nodes, drowsiness, pain in the joints and flu-like symptoms. Gastrointestinal symptoms that may occur include nausea, vomiting, loss of appetite, and diarrhea. Fewer than one-third of patients develop a rash.

- West Nile neuroinvasive disease (WNND), which occurs in less than 1 percent of cases, is when the virus infects the central nervous system resulting in meningitis, encephalitis, meningoencephalitis or a poliomyelitis-like syndrome. Many patients with WNND have normal neuroimaging studies, although abnormalities may be present in various cerebral areas including the basal ganglia, thalamus, cerebellum, and brainstem.

- West Nile virus encephalitis (WNE) is the most common neuroinvasive manifestation of WNND. WNE presents with similar symptoms to other viral encephalitis with fever, headaches, and altered mental status. A prominent finding in WNE is muscular weakness (30 to 50 percent of patients with encephalitis), often with lower motor neuron symptoms, flaccid paralysis, and hyporeflexia with no sensory abnormalities.

- West Nile meningitis (WNM) usually involves fever, headache, and stiff neck. Pleocytosis, an increase of white blood cells in cerebrospinal fluid, is also present. Changes in consciousness are not usually seen and are mild when present.

- West Nile meningoencephalitis is inflammation of both the brain (encephalitis) and meninges (meningitis).

- West Nile poliomyelitis (WNP), an acute flaccid paralysis syndrome associated with WNV infection, is less common than WNM or WNE. This syndrome is generally characterized by the acute onset of asymmetric limb weakness or paralysis in the absence of sensory loss. Pain sometimes precedes the paralysis. The paralysis can occur in the absence of fever, headache, or other common symptoms associated with WNV infection. Involvement of respiratory muscles, leading to acute respiratory failure, can sometimes occur.

- West-Nile reversible paralysis, Like WNP, the weakness or paralysis is asymmetric. Reported cases have been noted to have an initial preservation of deep tendon reflexes, which is not expected for a pure anterior horn involvement. Disconnect of upper motor neuron influences on the anterior horn cells possibly by myelitis or glutamate excitotoxicity have been suggested as mechanisms. The prognosis for recovery is excellent.

- Nonneurologic complications of WNV infection that may rarely occur include fulminant hepatitis, pancreatitis, myocarditis, rhabdomyolysis, orchitis, nephritis, optic neuritis and cardiac dysrhythmias and hemorrhagic fever with coagulopathy. Chorioretinitis may also be more common than previously thought.

- Cutaneous manifestations specifically rashes, are not uncommon in WNV-infected patients; however, there is a paucity of detailed descriptions in case reports and there are few clinical images widely available. Punctate erythematous, macular, and papular eruptions, most pronounced on the extremities have been observed in WNV cases and in some cases histopathologic findings have shown a sparse superficial perivascular lymphocytic infiltrate, a manifestation commonly seen in viral exanthems. A literature review provides support that this punctate rash is a common cutaneous presentation of WNV infection.

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.

Oropouche fever is characterized as a acute febrile illness, meaning that it begins with a sudden onset of a fever followed by severe clinical symptoms. It typically takes 4 to 8 days from the incubation period to first start noticing signs of infection, beginning from the bite of the infected mosquito or midge.

Fevers are the most common symptom with temperatures as high as 104F. Clinical symptoms include chills, headache, myalgia, arthralgia, dizziness, photophobia, vomiting, joint pains, epigastric pain, and rashes.

There also have been some cases where rashes resembles rubella and patients presented systematic symptoms including nausea, vomiting, diarrhea, conjunctive congestion, epigastric pain, and retro-orbitial pain.

The initial febrile episode typically passes after a few days, but it is very common to have a reoccurrence of these symptoms with a lesser intensity. Studies have shown this typically happens in about 60% of cases.

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".

Mayaro virus disease is a mosquitoborne zoonotic pathogen endemic to certain humid forests of tropical South America. Infection with Mayaro virus causes an acute, self-limited dengue-like illness of 3–5 days' duration. The causative virus, abbreviated MAYV, is in the family Togaviridae, and genus Alphavirus. It is closely related to other alphaviruses that produce a dengue-like illness accompanied by long-lasting arthralgia. It is only known to circulate in tropical South America.

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.

Signs and symptoms of VHFs include (by definition) fever and bleeding. Manifestations of VHF often also include flushing of the face and chest, small red or purple spots (petechiae), bleeding, swelling caused by edema, low blood pressure (hypotension), and shock. Malaise, muscle pain, headache, vomiting, and diarrhea occur frequently. The severity of symptoms varies with the type of virus. The “VHF syndrome” (capillary leak, bleeding diathesis, and circulatory compromise leading to shock) appears in a majority of people with filovirus hemorrhagic fevers (e.g., Ebola and Marburg virus), Crimean–Congo hemorrhagic fever (CCHF), and the South American hemorrhagic fevers caused by arenaviruses, but only in a small minority of patients with dengue, Rift Valley fever, and Lassa fever.

In sheep, BTV causes an acute disease with high morbidity and mortality. BTV also infects goats, cattle and other domestic animals as well as wild ruminants (for example, blesbuck, white-tailed deer, elk, and pronghorn antelope).

Major signs are high fever, excessive salivation, swelling of the face and tongue and cyanosis of the tongue. Swelling of the lips and tongue gives the tongue its typical blue appearance, though this sign is confined to a minority of the animals. Nasal signs may be prominent, with nasal discharge and stertorous respiration.

Some animals also develop foot lesions, beginning with coronitis, with consequent lameness. In sheep, this can lead to knee-walking. In cattle, constant changing of position of the feet gives bluetongue the nickname The Dancing Disease. Torsion of the neck (opisthotonos or torticollis) is observed in severely affected animals.

Not all animals develop signs, but all those that do lose condition rapidly, and the sickest die within a week. For affected animals which do not die, recovery is very slow, lasting several months.

The incubation period is 5–20 days, and all signs usually develop within a month. The mortality rate is normally low, but it is high in susceptible breeds of sheep. In Africa, local breeds of sheep may have no mortality, but in imported breeds it may be up to 90 percent.

In cattle, goats and wild ruminants infection is usually asymptomatic despite high virus levels in blood. Red deer are an exception, and in them the disease may be as acute as in sheep.

Viremia (UK: viraemia) is a medical condition where viruses enter the bloodstream and hence have access to the rest of the body. It is similar to "bacteremia", a condition where bacteria enter the bloodstream. The name comes from combining the word virus with the Greek word for blood ("haima"). It usually lasts for 4 to 5 days in the primary condition.

Equine viral arteritis (EVA) is a disease of horses caused by equine arteritis virus, an RNA virus of the genus "Arterivirus". The virus which causes EVA was first isolated in 1953, but the disease has afflicted equine animals worldwide for centuries. It has been more common in some breeds of horses in the United States, but there is no breed "immunity". In the UK, it is a notifiable disease. There is no known human hazard.

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 incubation period of the chikungunya virus ranges from one to twelve days, and is most typically three to seven. The disease may be asymptomatic, but generally is not, as 72% to 97% of those infected will develop symptoms. Characteristic symptoms include sudden onset with high fever, joint pain, and rash. Other symptoms may occur, including headache, fatigue, digestive complaints, and conjunctivitis.

Information gained during recent epidemics suggests that chikungunya fever may result in a chronic phase as well as the phase of acute illness. Within the acute phase, two stages have been identified: a viral stage during the first five to seven days, during which viremia occurs, followed by a convalescent stage lasting approximately ten days, during which symptoms improve and the virus cannot be detected in the blood. Typically, the disease begins with a sudden high fever that lasts from a few days to a week, and sometimes up to ten days. The fever is usually above and sometimes reaching and may be biphasic—lasting several days, breaking, and then returning. Fever occurs with the onset of viremia, and the level of virus in the blood correlates with the intensity of symptoms in the acute phase. When IgM, an antibody that is a response to the initial exposure to an antigen, appears in the blood, viremia begins to diminish. However, headache, insomnia and an extreme degree of exhaustion remain, usually about five to seven days.

Following the fever, strong joint pain or stiffness occurs; it usually lasts weeks or months, but may last for years. The joint pain can be debilitating, often resulting in near immobility of the affected joints. Joint pain is reported in 87–98% of cases, and nearly always occurs in more than one joint, though joint swelling is uncommon. Typically the affected joints are located in both arms and legs, and are affected symmetrically. Joints are more likely to be affected if they have previously been damaged by disorders such as arthritis. Pain most commonly occurs in peripheral joints, such as the wrists, ankles, and joints of the hands and feet as well as some of the larger joints, typically the shoulders, elbows and knees. Pain may also occur in the muscles or ligaments.

Rash occurs in 40–50% of cases, generally as a maculopapular rash occurring two to five days after onset of symptoms. Digestive symptoms, including abdominal pain, nausea, vomiting or diarrhea, may also occur. In more than half of cases, normal activity is limited by significant fatigue and pain. Infrequently, inflammation of the eyes may occur in the form of iridocyclitis, or uveitis, and retinal lesions may occur.

Temporary damage to the liver may occur.

Rarely, neurological disorders have been reported in association with chikungunya virus, including Guillain–Barré syndrome, palsies, meningoencephalitis, flaccid paralysis and neuropathy. In contrast to dengue fever, Chikungunya fever very rarely causes hemorrhagic complications. Symptoms of bleeding should lead to consideration of alternative diagnoses or co-infection with dengue fever or coexisting congestive hepatopathy.

Herpes gladiatorum is characterized by a rash with clusters of sometimes painful fluid-filled blisters, often on the neck, chest, face, stomach, and legs. The infection is often accompanied by lymphadenopathy (enlargement of the lymph nodes), fever, sore throat, and headache. Often, the accompanying symptoms are much more of an inconvenience than the actual skin blisters and rash.

Each blister contains infectious virus particles (virions). Close contact, particularly abrasive contact as found in contact sports, causes the infected blisters to burst and pass the infection along. Autoinoculation (self-infection) can occur through self-contact, leading to infection at multiple sites on the body.

Herpes gladiatorum symptoms may last up to a few weeks, and if they occur during the first outbreak, they can be more pronounced. In recurrences of the ailment, symptoms are milder, even if lesions still tend to occur. With recurrent infections scabs may form at 3 days yet the lesions are still considered infectious up til 6.4 days after starting oral antiviral medications. Healing takes place without leaving scars. It is possible that the condition evolves asymptomatically and sores are never present.

West Nile fever is a viral infection typically spread by mosquitoes. In about 75% of infections people have few or no symptoms. About 20% of people develop a fever, headache, vomiting, or a rash. In less than 1% of people, encephalitis or meningitis occurs, with associated neck stiffness, confusion, or seizures. Recovery may take weeks to months. The risk of death among those in whom the nervous system is affected is about 10%.

West Nile virus is typically spread by infected mosquitoes. Mosquitoes become infected when they feed on infected birds. Rarely the virus is spread through blood transfusions, organ transplants, or from mother to baby during pregnancy, delivery, or breastfeeding. It otherwise does not spread directly between people. Risks for severe disease include age over 60 and other health problems. Diagnosis is typically based on symptoms and blood tests.

There is no human vaccine. The best method to reduce the risk of infections is avoiding mosquito bites. This may be done by eliminating standing pools of water, such as in old tires, buckets, gutters, and swimming pools. Mosquito repellent, window screens, mosquito nets, and avoiding areas where mosquitoes occur may also be useful. While there is no specific treatment, pain medications may be useful.

WNV occurs in Europe, the Middle East, Africa, India, Asia, Australia, and North America. In the United States thousands of cases are reported a year, with most occurring in August and September. It can occur in outbreaks of disease. The virus was discovered in Uganda in 1937 and was first detected in North America in 1999. Severe disease may also occur in horses and a vaccine for these animals is available. A surveillance system in birds is useful for early detection of a potential human outbreak.