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.

DIPs are a naturally occurring phenomenon that can also be synthesized for experimental use. They are spontaneously produced by error-prone viral replication, something particularly prevalent in RNA viruses over DNA viruses due to the enzyme used (replicase, or RNA-dependent RNA polymerase.) DI genomes typically retain the termini sequences needed for recognition by viral polymerases, and sequences for packaging of their genome into new particles, but little else. The size of the genomic deletion event can vary greatly, with one such example in a DIP derived from rabies virus exhibiting a 6.1 kb deletion. In another example, the size of several DI-DNA plant virus genomes varied from one tenth of the size of the original genome to one half.

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.

Prevention is effected via quarantine, inoculation with live modified virus vaccine and control of the midge vector, including inspection of aircraft.

However, simple husbandry changes and practical midge control measures may help break the livestock infection cycle. Housing livestock during times of maximum midge activity (from dusk to dawn) may lead to significantly reduced biting rates. Similarly, protecting livestock shelters with fine mesh netting or coarser material impregnated with insecticide will reduce contact with the midges. The "Culicoides" midges that carry the virus usually breed on animal dung and moist soils, either bare or covered in short grass. Identifying breeding grounds and breaking the breeding cycle will significantly reduce the local midge population. Turning off taps, mending leaks and filling in or draining damp areas will also help dry up breeding sites. Control by trapping midges and removing their breeding grounds may reduce vector numbers. Dung heaps or slurry pits should be covered or removed, and their perimeters (where most larvae are found) regularly scraped.

Once a virus is in a cell, it will activate formation of proteins (either by itself or using the host) to gain full control of the host cell, if it is able to. Control mechanisms include the suppression of intrinsic cell defenses, suppression of cell signaling and suppression of host cellular transcription and translation. Often, it is these cytotoxic effects that lead to the death and decline of a cell infected by a virus.

A cell is classified as susceptible to a virus if the virus is able to enter the cell. After the introduction of the viral particle, unpacking of the contents (viral proteins in the tegument and the viral genome via some form of nucleic acid) occurs as preparation of the next stage of viral infection: viral replication.

The serious complications of HiB are brain damage, hearing loss, and even death.

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.

Most strains of "H. influenzae" are opportunistic pathogens; that is, they usually live in their host without causing disease, but cause problems only when other factors (such as a viral infection, reduced immune function or chronically inflamed tissues, e.g. from allergies) create an opportunity. They infect the host by sticking to the host cell using trimeric autotransporter adhesins.

Naturally acquired disease caused by "H. influenzae" seems to occur in humans only. In infants and young children, "H. influenzae" type b (Hib) causes bacteremia, pneumonia, epiglottitis and acute bacterial meningitis. On occasion, it causes cellulitis, osteomyelitis, and infectious arthritis. It is one cause of neonatal infection.

Due to routine use of the Hib conjugate vaccine in the U.S. since 1990, the incidence of invasive Hib disease has decreased to 1.3/100,000 in children. However, Hib remains a major cause of lower respiratory tract infections in infants and children in developing countries where the vaccine is not widely used. Unencapsulated "H. influenzae" strains are unaffected by the Hib vaccine and cause ear infections (otitis media), eye infections (conjunctivitis), and sinusitis in children, and are associated with pneumonia.

Penicillin is used to treat neurosyphilis; however, early diagnosis and treatment is critical. Two examples of penicillin therapies include:

- Aqueous penicillin G 3–4 million units every four hours for 10 to 14 days.

- One daily intramuscular injection and oral probenecid four times daily, both for 10 to 14 days.

Follow-up blood tests are generally performed at 3, 6, 12, 24, and 36 months to make sure the infection is gone. Lumbar punctures for CSF fluid analysis are generally performed every 6 months.

Neurosyphilis was almost at the point being unheard of in the United States after penicillin therapy was introduced. However, concurrent infection of "T. pallidum" with human immunodeficiency virus (HIV) has been found to affect the course of syphilis. Syphilis can lie dormant for 10 to 20 years before progressing to neurosyphilis, but HIV may accelerate the rate of the progress. Also, infection with HIV has been found to cause penicillin therapy to fail more often. Therefore, neurosyphilis has once again been prevalent in societies with high HIV rates and limited access to penicillin. Blood testing for syphilis was once required in order to obtain a marriage license in most U.S. states, but that requirement has been discontinued by all 50 states over recent years, also contributing to the spread of the disease.

In the world less than 1 in 1.00.000 have HIDS [5]. 200 individuals throughout the world do suffer from MVK.

Mevalonate kinase deficiency causes an accumulation of mevalonic acid in the urine, resulting from insufficient activity of the enzyme mevalonate kinase (ATP:mevalonate 5-phosphotransferase; EC 2.7.1.36).

The disorder was first described in 1985.

Classified as an inborn error of metabolism, mevalonate kinase deficiency usually results in developmental delay, hypotonia, anemia, hepatosplenomegaly, various dysmorphic features, mental retardation, an overall failure to thrive and several other features.

A review from 2000 stated that life expectancy was reduced because of a tendency to develop cancer relatively early as well as deaths due to infections related to immunodeficiency.

PNP-deficiency is extremely rare. Only 33 patients with the disorder in the United States have been documented. In the United Kingdom only one child has been diagnosed with this disorder.

Myocarditis has been documented at autopsy in 40–52% of patients who died of AIDS before the introduction of HAART. Toxoplasma gondii is the most common opportunistic infectious agent associated with myocarditis in AIDS occurring in 12% of deaths from AIDS 1987-1991 in one autopsy series. Myocardial toxoplasmosis causes an increase in the myocardial fraction of creatine kinase (CK-MB).

In situ hybridization or polymerase chain reaction studies illustrate a high frequency of cytomegalovirus and HIV-1 in AIDS patients with lymphocytic myocarditis and severe left ventricular dysfunction. Thus, it supports the hypothesis that HIV-1 has a pathogenetic action and influences dilated cardiomyopathy.

Coinfection with viruses (usually, coxsackievirus B3 and cytomegalovirus) seems to have an important effect as the GISCA autopsy records show that 83% of patients with myocarditis and 50% with dilated cardiomyopathy were coinfected with viruses.

Dilated cardiomyopathy can be due to pericardial effusion or infective endocarditis, especially in intravenous drug users which are common in the HIV population. However, the most researched cause of cardiomyopathy is myocarditis (myocardial inflammation and infection) caused by HIV-1, which the main subtype of HIV (the other being HIV-2), with greater likelihood of transmission and shorter period between infection and illness. HIV-1 virions infect cardiomyocytes in patches but there is no direct correlation between viral infection and dysfunction of cardiomyocytes.

HIV-related cardiomyopathy is often not associated with any specific opportunistic infection, and approximately 40% of patients have not experienced any opportunistic infection before the onset of cardiac symptoms.

In addition to evaluation of any symptoms and signs, various blood tests can be done:

- Venereal Disease Research Laboratory test (VDRL)

- Fluorescent treponemal antibody absorption (FTA-ABS)

- Rapid plasma reagin (RPR)

- Treponema pallidum particle agglutination assay (TPPA)

Also, it is important to test the cerebrospinal fluid for signs of syphilis.

Additional tests to look for problems with the nervous system may include the following:

- Cerebral angiogram

- Head CT scan

- Lumbar puncture ("spinal tap") to acquire a sample for cerebrospinal fluid analysis

- MRI scan of the brain, brainstem, or spinal cord

Sarcosinemia (SAR), also called hypersarcosinemia and SARDH deficiency, is a rare autosomal recessive metabolic disorder characterized by an increased concentration of sarcosine in blood plasma and urine ("sarcosinuria"). It can result from an inborn error of sarcosine metabolism, or from severe folate deficiency related to the folate requirement for the conversion of sarcosine to glycine. It is thought to be a relatively benign condition.

Acheiropodia (ACHP), also known as Horn-Kolb Syndrome, Acheiropody and Aleijadinhos (Brazilian type), is an autosomal recessive disorder that results in hemimelia, a lack of formation of the distal extremities.

This is a congenital defect which consists of bilateral amputations of the distal upper and lower extremities, as well as aplasia of the hands and feet. It was first discovered and is prevalent almost exclusively in Brazil.

A mutation in the ZNHIT3 gene - a nuclear zinc finger protein involved in transcriptional regulation and in small nucleolar ribonucleoprotein particle assembly has been shown to be the cause of the Finnish-type of PEHO syndrome. However, the syndrome appear to be genetically heterogeneous and it might reflect an underlying genetic tubulinopathy, with biallelic mutations in the gene PRUNE1 also identified in non-Finnish patients with PEHO syndrome.

The life expectancy for individuals with Salla disease is between the ages of 50 and 60.

The cause of the inflammation remains unknown, with various theories of it occurring as an autoimmune response to a mild infection, or the possibility of it being viral because of the preceding flu-like illness that generally accompanies it. It is usually associated with HLA-B7 and HLA-DR2.

PEHO syndrome is a progressive encephalopathy with edema, hypsarrhythmia and optic atrophy. It is a very rare disease, one of the Finnish heritage diseases, although approximately half of the cases reported so far are not-Finnish and have been described worldwide .

It has been suggested that it may also be present in Australian and American populations.

Vision improves in almost all cases. In rare cases, a patient may suffer permanent visual loss associated with lesions on their optic nerve.

Rarely, coexisting vasculitis may cause neurological complications. These occurrences can start with mild headaches that steadily worsen in pain and onset, and can include attacks of dysesthesia. This type of deterioration happens usually if the lesions involve the fovea.

Nijmegen breakage syndrome (NBS), also known as Berlin breakage syndrome, ataxia telangiectasia variant 1 (AT-V1) and Seemanova syndrome, is a rare autosomal recessive congenital disorder causing chromosomal instability, probably as a result of a defect in the double Holliday junction DNA repair mechanism and/or the synthesis dependent strand annealing mechanism for repairing double strand breaks in DNA (see Homologous recombination).

NBS1 codes for a protein (nibrin) that has two major functions: (1) to stop the cell cycle in the S phase, when there are errors in the cell DNA (2) to interact with FANCD2 that can activate the BRCA1/BRCA2 pathway of DNA repair. This explains why mutations in the NBS1 gene lead to higher levels of cancer (see Fanconi anemia, Cockayne syndrome.)

The name derives from the Dutch city Nijmegen where the condition was first described.

Most people with NBS have West Slavic origins. The largest number of them live in Poland.