There is no vaccine for SARS to date. Isolation and quarantine remain the most effective means to prevent the spread of SARS. Other preventative measures include:

- Handwashing

- Disinfection of surfaces for fomites

- Wearing a surgical mask

- Avoiding contact with bodily fluids

- Washing the personal items of someone with SARS in hot, soapy water (eating utensils, dishes, bedding, etc.)

- Keeping children with symptoms home from school

Many public health interventions were taken to help control the spread of the disease; which is mainly spread through respiratory droplets in the air. These interventions included earlier detection of the disease, isolation of people who are infected, droplet and contact precautions, and the use of personal protective equipment (PPE); including masks and isolation gowns. A screening process was also put in place at airports to monitor air travel to and from affected countries. Although no cases have been identified since 2004, the CDC is still working to make federal and local rapid response guidelines and recommendations in the event of a reappearance of the virus.

Several consequent reports from China on some recovered SARS patients showed severe long-time sequelae exist. The most typical diseases include, among other things, pulmonary fibrosis, osteoporosis, and femoral necrosis, which have led to the complete loss of working ability or even self-care ability of these cases. As a result of quarantine procedures, some of the post-SARS patients have been documented suffering from posttraumatic stress disorder (PTSD) and major depressive disorder.

MERS cases have been reported to have low white blood cell count, and in particular low lymphocytes.

For PCR testing, the WHO recommends obtaining samples from the lower respiratory tract via bronchoalveolar lavage (BAL), sputum sample or tracheal aspirate as these have the highest viral loads. There have also been studies utilizing upper respiratory sampling via nasopharyngeal swab.

Several highly sensitive, confirmatory real-time RT-PCR assays exist for rapid identification of MERS-CoV from patient-derived samples. These assays attempt to amplify upE (targets elements upstream of the E gene), open reading frame 1B (targets the ORF1b gene) and open reading frame 1A (targets the ORF1a gene). The WHO recommends the upE target for screening assays as it is highly sensitive. In addition, hemi-nested sequencing amplicons targeting RdRp (present in all coronaviruses) and nucleocapsid (N) gene (specific to MERS-CoV) fragments can be generated for confirmation via sequencing. Reports of potential polymorphisms in the N gene between isolates highlight the necessity for sequence-based characterization.

The WHO recommended testing algorithm is to start with an upE RT-PCR and if positive confirm with ORF 1A assay or RdRp or N gene sequence assay for confirmation. If both an upE and secondary assay are positive it is considered a confirmed case.

Protocols for biologically safe immunofluorescence assays (IFA) have also been developed; however, antibodies against betacoronaviruses are known to cross-react within the genus. This effectively limits their use to confirmatory applications. A more specific protein-microarray based assay has also been developed that did not show any cross-reactivity against population samples and serum known to be positive for other betacoronaviruses. Due to the limited validation done so far with serological assays, WHO guidance is that "cases where the testing laboratory has reported positive serological test results in the absence of PCR testing or sequencing, are considered probable cases of MERS-CoV infection, if they meet the other conditions of that case definition."

According to World Health Organization, the interim case definition is that a confirmed case is identified in a person with a positive lab test by "molecular diagnostics including either a positive PCR on at least two specific genomic targets or a single positive target with sequencing on a second."

Based on the low variability exhibited among known SARS-CoV-2 genomic sequences, the strain is thought to have been detected by health authorities within weeks of its emergence among the human population in late 2019. The earliest case of infection currently known is thought to have been found on 17 November 2019. The virus subsequently spread to all provinces of China and to more than 150 other countries in Asia, Europe, North America, South America, Africa, and Oceania. Human-to-human transmission of the virus has been confirmed in all of these regions. On 30 January 2020, SARS-CoV-2 was designated a Public Health Emergency of International Concern by the WHO, and on 11 March 2020 the WHO declared it a pandemic.

The basic reproduction number (R0) of the virus has been estimated to be between 1.4 and 3.9. This means that each infection from the virus is expected to result in 1.4 to 3.9 new infections when no members of the community are immune and no preventive measures are taken. The reproduction number may be higher in densely populated conditions such as those found on cruise ships. Many forms of preventive efforts may be employed in specific circumstances in order to reduce the propagation of the virus.

There have been about 82,000 confirmed cases of infection in mainland China. While the proportion of infections that result in confirmed cases or progress to diagnosable disease remains unclear, one mathematical model estimated that on 25 January 2020 75,815 people were infected in Wuhan alone, at a time when the number of confirmed cases worldwide was only 2,015. Before 24 February 2020, over 95% of all deaths from COVID-19 worldwide had occurred in Hubei province, where Wuhan is located. As of 17 April 2020, the percentage had decreased to 2.1%.

As of 17 April 2020, there have been 2,234,109 total confirmed cases of SARS-CoV-2 infection in the ongoing pandemic. The total number of deaths attributed to the virus is 153,379. Many recoveries from confirmed infections go unreported, but at least 567,695 people have recovered from confirmed infections.

Human-to-human transmission of SARS-CoV-2 has been confirmed during the 2019–20 coronavirus pandemic. Transmission occurs primarily via respiratory droplets from coughs and sneezes within a range of about 1.8 metres (6 ft). Indirect contact via contaminated surfaces is another possible cause of infection. Preliminary research indicates that the virus may remain viable on plastic and steel for up to three days, but does not survive on cardboard for more than one day or on copper for more than four hours; the virus is inactivated by soap, which destabilises its lipid bilayer. Viral RNA has also been found in stool samples from infected individuals.

The degree to which the virus is infectious during the incubation period is uncertain, but research has indicated that the pharynx reaches peak viral load approximately four days after infection. On 1 February 2020, the World Health Organization (WHO) indicated that "transmission from asymptomatic cases is likely not a major driver of transmission". However, an epidemiological model of the beginning of the outbreak in China suggested that "pre-symptomatic shedding may be typical among documented infections" and that subclinical infections may have been the source of a majority of infections.

There is some evidence of human-to-animal transmission of SARS-CoV-2, including examples in felids. Some institutions have advised those infected with SARS-CoV-2 to restrict contact with animals.

The best prevention against viral pneumonia is vaccination against influenza, adenovirus, chickenpox, herpes zoster, measles, and rubella.

The WHO has published several testing protocols for the disease. The standard method of testing is real-time reverse transcription polymerase chain reaction (rRT-PCR). The test is typically done on respiratory samples obtained by a nasopharyngeal swab; however, a nasal swab or sputum sample may also be used. Results are generally available within a few hours to two days. Blood tests can be used, but these require two blood samples taken two weeks apart and the results have little immediate value. Chinese scientists were able to isolate a strain of the coronavirus and publish the genetic sequence so laboratories across the world could independently develop polymerase chain reaction (PCR) tests to detect infection by the virus. As of 4 April 2020, antibody tests (which may detect active infections and whether a person had been infected in the past) were in development, but not yet widely used. The Chinese experience with testing has shown the accuracy is only 60 to 70%. The FDA in the United States approved the first point-of-care test on 21 March 2020 for use at the end of that month.

Diagnostic guidelines released by Zhongnan Hospital of Wuhan University suggested methods for detecting infections based upon clinical features and epidemiological risk. These involved identifying people who had at least two of the following symptoms in addition to a history of travel to Wuhan or contact with other infected people: fever, imaging features of pneumonia, normal or reduced white blood cell count or reduced lymphocyte count.

A study asked hospitalized COVID-19 patients to cough into a sterile container, thus producing a saliva sample, and detected virus in eleven of twelve patients using RT-PCR. This technique has the potential of being quicker than a swab and involving less risk to health care workers (collection at home or in the car).

Along with laboratory testing, chest CT scans may be helpful to diagnose COVID-19 in individuals with a high clinical suspicion of infection but is not recommended for routine screening. Bilateral multilobar ground-glass opacities with a peripheral, asymmetric and posterior distribution are common in early infection. Subpleural dominance, crazy paving (lobular septal thickening with variable alveolar filling), and consolidation may appear as the disease progresses.

Diagnosis of BMCF depends on a combination of history and symptoms, histopathology and detection in the blood or tissues of viral antibodies by ELISA or of viral DNA by PCR. The characteristic histologic lesions of MCF are lymphocytic arteritis with necrosis of the blood vessel wall and the presence of large T lymphocytes mixed with other cells. The similarity of MCF clinical signs to other enteric diseases, for example blue tongue, mucosal disease and foot and mouth make laboratory diagnosis of MCF important. The world organisation for animal health recognises histopathology as the definitive diagnostic test, but laboratories have adopted other approaches with recent developments in molecular virology. No vaccine has as yet been developed.

In cases of viral pneumonia where influenza A or B are thought to be causative agents, patients who are seen within 48 hours of symptom onset may benefit from treatment with oseltamivir or zanamivir. Respiratory syncytial virus (RSV) has no direct acting treatments, but ribavirin in indicated for severe cases. Herpes simplex virus and varicella-zoster virus infections are usually treated with aciclovir, whilst ganciclovir is used to treat cytomegalovirus. There is no known efficacious treatment for pneumonia caused by SARS coronavirus, MERS coronavirus, adenovirus, hantavirus, or parainfluenza. Care is largely supportive.

Few data are available about microscopic lesions and the pathophysiology of COVID-19. The main pathological findings at autopsy are:

- Macroscopy: pleurisy, pericarditis, lung consolidation and pulmonary oedema

- Four types of severity of viral pneumonia can be observed:

- minor pneumonia: minor serous exudation, minor fibrin exudation

- mild pneumonia: pulmonary oedema, pneumocyte hyperplasia, large atypical pneumocytes, interstitial inflammation with lymphocytic infiltration and multinucleated giant cell formation

- severe pneumonia: diffuse alveolar damage (DAD) with diffuse alveolar exudates. DAD is the cause of acute respiratory distress syndrome (ARDS) and severe hypoxemia.

- healing pneumonia: organisation of exudates in alveolar cavities and pulmonary interstitial fibrosis

- plasmocytosis in BAL

- Blood: disseminated intravascular coagulation (DIC); leukoerythroblastic reaction

- Liver: microvesicular steatosis

Vaccination helps prevent bronchopneumonia, mostly against influenza viruses, adenoviruses, measles, rubella, streptococcus pneumoniae, haemophilus influenzae, diphtheria, bacillus anthracis, chickenpox, and bordetella pertussis.

Antibiotics do not help the many lower respiratory infections which are caused by parasites or viruses. While acute bronchitis often does not require antibiotic therapy, antibiotics can be given to patients with acute exacerbations of chronic bronchitis. The indications for treatment are increased dyspnoea, and an increase in the volume or purulence of the sputum. The treatment of bacterial pneumonia is selected by considering the age of the patient, the severity of the illness and the presence of underlying disease. Amoxicillin and doxycycline are suitable for many of the lower respiratory tract infections seen in general practice.

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.

Chest radiographs (X-ray photographs) often show a pulmonary infection before physical signs of atypical pneumonia are observable at all.

This is occult pneumonia. In general, occult pneumonia is rather often present in patients with pneumonia and can also be caused by "Streptococcus pneumoniae", as the decrease of occult pneumonia after vaccination of children with a pneumococcal vaccine suggests.

Infiltration commonly begins in the perihilar region (where the bronchus begins) and spreads in a wedge- or fan-shaped fashion toward the periphery of the lung field. The process most often involves the lower lobe, but may affect any lobe or combination of lobes.

In patients managed in the community, determining the causative agent is not cost-effective and typically does not alter management. For people who do not respond to treatment, sputum culture should be considered, and culture for "Mycobacterium tuberculosis" should be carried out in persons with a chronic productive cough. Testing for other specific organisms may be recommended during outbreaks, for public health reasons. In those hospitalized for severe disease, both sputum and blood cultures are recommended, as well as testing the urine for antigens to "Legionella" and "Streptococcus". Viral infections can be confirmed via detection of either the virus or its antigens with culture or polymerase chain reaction (PCR), among other techniques. The causative agent is determined in only 15% of cases with routine microbiological tests.

Mycoplasma is found more often in younger than in older people.

Older people are more often infected by Legionella.

A chest radiograph is frequently used in diagnosis. In people with mild disease, imaging is needed only in those with potential complications, those not having improved with treatment, or those in which the cause is uncertain. If a person is sufficiently sick to require hospitalization, a chest radiograph is recommended. Findings do not always match the severity of disease and do not reliably separate between bacterial infection and viral infection.

X-ray presentations of pneumonia may be classified as lobar pneumonia, bronchopneumonia (also known as lobular pneumonia), and interstitial pneumonia. Bacterial, community-acquired pneumonia classically show lung consolidation of one lung segmental lobe, which is known as lobar pneumonia. However, findings may vary, and other patterns are common in other types of pneumonia. Aspiration pneumonia may present with bilateral opacities primarily in the bases of the lungs and on the right side. Radiographs of viral pneumonia may appear normal, appear hyper-inflated, have bilateral patchy areas, or present similar to bacterial pneumonia with lobar consolidation. Radiologic findings may not be present in the early stages of the disease, especially in the presence of dehydration, or may be difficult to be interpreted in the obese or those with a history of lung disease. A CT scan can give additional information in indeterminate cases. Lung ultrasound may also be useful in helping to make the diagnosis.

On post-mortem examination (necropsy), the most obvious gross lesion is subcutaneous oedema in the submandibular and pectoral (brisket) regions. Petechial haemorrhages are found subcutaneously and in the thoracic cavity. In addition, congestion and various degrees of consolidation of the lung may occur. Animals that die within 24–36 hours, have only few petechial haemorrhages on the heart and generalised congestion of the lung, while in animals that die after 72 hours, petechial and ecchymotic haemorrhages were more evident and lung consolidation are more extensive.

Patients with symptoms of CAP require evaluation. Diagnosis of pneumonia is made clinically, rather than on the basis of a particular test. Evaluation begins with a physical examination by a health provider, which may reveal fever, an increased respiratory rate (tachypnea), low blood pressure (hypotension), a fast heart rate (tachycardia) and changes in the amount of oxygen in the blood. Palpating the chest as it expands and tapping the chest wall (percussion) to identify dull, non-resonant areas can identify stiffness and fluid, signs of CAP. Listening to the lungs with a stethoscope (auscultation) can also reveal signs associated with CAP. A lack of normal breath sounds or the presence of crackles can indicate fluid consolidation. Increased vibration of the chest when speaking, known as tactile fremitus, and increased volume of whispered speech during auscultation can also indicate fluid.

When signs of pneumonia are discovered during evaluation, chest X-rays, are performed to support a diagnosis of CAP, and examination of the blood and sputum for infectious microorganisms and blood tests may be used to support a diagnosis of CAP. Diagnostic tools depend on the severity of illness, local practices and concern about complications of the infection. All patients with CAP should have their blood oxygen monitored with pulse oximetry. In some cases, arterial blood gas analysis may be required to determine the amount of oxygen in the blood. A complete blood count (CBC) may reveal extra white blood cells, indicating infection.

Chest X-rays and X-ray computed tomography (CT) can reveal areas of opacity (seen as white), indicating consolidation. CAP does not always appear on x-rays, because the disease is in its initial stages or involves a part of the lung an x-ray does not see well. In some cases, chest CT can reveal pneumonia not seen on x-rays. However, congestive heart failure or other types of lung damage can mimic CAP on x-rays.

Several tests can identify the cause of CAP. Blood cultures can isolate bacteria or fungi in the bloodstream. Sputum Gram staining and culture can also reveal the causative microorganism. In severe cases, bronchoscopy can collect fluid for culture. Special tests can be performed if an uncommon microorganism is suspected, such as urinalysis for Legionella antigen in Legionnaires' disease.

CAP may be prevented by treating underlying illnesses increasing its risk, by smoking cessation and vaccination of children and adults. Vaccination against "haemophilus influenzae" and "streptococcus pneumoniae" in the first year of life has reduced their role in childhood CAP. A vaccine against "streptococcus pneumoniae", available for adults, is recommended for healthy individuals over 65 and all adults with COPD, heart failure, diabetes mellitus, cirrhosis, alcoholism, cerebrospinal fluid leaks or who have had a splenectomy. Re-vaccination may be required after five or ten years.

Patients who are vaccinated against "streptococcus pneumoniae", health professionals, nursing-home residents and pregnant women should be vaccinated annually against influenza. During an outbreak, drugs such as amantadine, rimantadine, zanamivir and oseltamivir have been demonstrated to prevent influenza.

There is some evidence that there may be a relationship between BoDV-1 infection and psychiatric disease.

In 1990, Janice E. Clements and colleagues reported in the journal "Science" that antibodies to a protein encoded by the BoDV-1 genome are found in the blood of patients with behavioral disorders. In the early 1990s, researchers in Germany, America, and Japan conducted an investigation of 5000 patients with psychiatric disorders and 1000 controls, in which a significantly higher percentage of patients than controls were positive for BoDV-1 antibodies. Subsequent studies have also presented evidence for an association between BoDV-1 and human psychiatric disorders. However, not all researchers consider the link between BoDV-1 and human psychiatric disease to be conclusively proven. A recent study found no BoDV-1 antibodies in 62 patients with the deficit form of schizophrenia.

Additional evidence for a role of BoDV-1 in psychiatric disorders comes from reports that the drug amantadine, which is used to treat influenza infections, has had some success in treating depression and clearing BoDV-1 infection. Counter-claims state that Borna virus infections are not cleared by amantadine. The issue is further complicated by the fact that amantadine is also used in the treatment of Parkinson's disease and may have direct effects on the nervous system.

François Madec, a French author, has written many recommendations on how reduce PMWS symptoms. They are mostly measures for disinfection, management, and hygiene, referred to as the "20 Madec Points" [Madec & Waddilove, 2002].

These measures have recently been expanded upon by Dr. David Barcellos, a professor at the Veterinary College in the Universidade Federal do Rio Grande do Sul, Rio Grande do Sul, Brazil. He presented these points at "1st Universidade Federal do Rio Grande do Sul Symposium about swine management, reproduction, and hygiene".

He divided his points by pig growth stage, and they can be loosely summarized as:

- keep the gutters clean

- increase feeder space

- use pens or small cages with solid dividers

- avoid mixing pigs from different origins

- improve the quality of air

- decrease maximum capacity, giving each pig more room

- separate sick animals as soon as possible, and treat them in a hospital pen. If they do not respond to antibiotics in three days, they should be culled

- control access of people and other animals

- reduce invironmental stress factors such as gases and air currents

- use immunizations and preventive medications for secondary agents commonly associated with PMWS

Methicillin-resistant Staphylococcus aureus (MRSA) evolved from Methicillin-susceptible Staphylococcus aureus (MSSA) otherwise known as common "S. aureus". Many people are natural carriers of "S. aureus", without being affected in any way. MSSA was treatable with the antibiotic methicillin until it acquired the gene for antibiotic resistance. Though genetic mapping of various strains of MRSA, scientists have found that MSSA acquired the mecA gene in the 1960s, which accounts for its pathogenicity, before this it had a predominantly commensal relationship with humans. It is theorized that when this "S. aureus" strain that had acquired the mecA gene was introduced into hospitals, it came into contact with other hospital bacteria that had already been exposed to high levels of antibiotics. When exposed to such high levels of antibiotics, the hospital bacteria suddenly found themselves in an environment that had a high level of selection for antibiotic resistance, and thus resistance to multiple antibiotics formed within these hospital populations. When "S. aureus" came into contact with these populations, the multiple genes that code for antibiotic resistance to different drugs were then acquired by MRSA, making it nearly impossible to control. It is thought that MSSA acquired the resistance gene through the horizontal gene transfer, a method in which genetic information can be passed within a generation, and spread rapidly through its own population as was illustrated in multiple studies. Horizontal gene transfer speeds the process of genetic transfer since there is no need to wait an entire generation time for gene to be passed on. Since most antibiotics do not work on MRSA, physicians have to turn to alternative methods based in Darwinian medicine. However prevention is the most preferred method of avoiding antibiotic resistance. By reducing unnecessary antibiotic use in human and animal populations, antibiotics resistance can be slowed.

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.