Mycobacteria are a type of germ. There are many different kinds. The most common one causes tuberculosis. Another one causes leprosy. Still others cause infections that are called atypical mycobacterial infections. They aren't "typical" because they don't cause tuberculosis. But they can still harm people, especially people with other problems that affect their immunity, such as AIDS.

Sometimes you can have these infections with no symptoms at all. At other times, they can cause lung symptoms similar to tuberculosis:

• Cough
• Weight loss
• Coughing up blood or mucus
• Weakness or fatigue
• Fever and chills
• Night sweats
• Lack of appetite and weight loss

Medicines can treat these infections, but often more than one is needed to cure the infection.

Mycobacterium malmoense (M. malmoense) is a bacterium naturally found in the environment, such as in wet soil, house dust, water, dairy products, domestic and wild animals, food, and human waste. M. malmoense infections most often occur in adults with lung disease, and manifests as a lung infection. Skin and tissue infections with M. malmoense have also been described. In young children, M. Malmoense may cause an infection of lymphnodes in the neck (i.e., cervical lymphadenitis).

Mycobacterium avium complex (MAC) refers to infections caused by two types of bacteria: Mycobacteriumavium and Mycobacteriumintracellulare. MAC bacteria do not make most people sick. However, people with immune systems that do not work well (from HIV/AIDS or certain cancers for example) or people with lung disease (such as chronic obstructive pulmonary disease (COPD) or cystic fibrosis) are at the greatest risk for getting sick from MAC Infections. Elderly women are also at higher risk to get sick from MAC infections.

There are 3 types of MAC infections.

• Pulmonary MAC infections - Affect the lungs and are the most common type. These mainly affect elderly women and people who already have lung disease.
• Disseminated MAC infections - Have spread throughout the body. This type is usually seen in people with advanced AIDS.
• MAC-associated lymphadenitis - Causes swelling of the lymph nodes (especially in the neck) and is the most common in young children who have normal immune systems.

While the symptoms are different for each type of infection, general symptoms include fever, night sweats, weight loss, and fatigue. MAC bacteria are found in water, soil, and dust. They infect people when the bacteria are inhaled or swallowed. MAC bacteria are not usually spread from person to person. MAC infections are diagnosed by a combination of imaging scans and identifying the bacteria in cultures of cells from the infected area. Treatment for MAC infection depends on the type and may include antibiotics, antiviral medications, or surgery.

Mendelian susceptibility to mycobacterial diseases (MSMD) is a rare immunodeficiency syndrome, with susceptibility to mycobacteria, such as the vaccine against tuberculosis (bacillus Calmette-Guérin (BCG) and environmental mycobacteria. It is characterized by severe, recurrent infections, either systemic (widespread) or localized. It has many subtypes. The most serious types are the autosomal recessive complete interferon gamma receptor 1 (IFN-gammaR1) and receptor 2 (IFN-gammaR2) deficiencies.

MSMD due to partial IFN-gammaR1, partial IFN-gammaR2, complete IL-12R-beta1, complete IL12B, complete ISG15, partial STAT1 and partial IRF8 deficiencies and MSMD due to partial X-linked recessive (XR) mutations are less severe subtypes. Only about half of patients with MSMD have an identified genetic cause. Nine genes are known to be responsible for MSMD. Seven of them are inherited in an autosomal recessive or autosomal dominant pattern (IFNGR1, IFNGR2, STAT1, IL12B, IL12RB1, IRF8 and ISG15 genes) and 2 are X-linked (IKBKG and CYBB genes). BCG vaccination should be avoided in those with MSMD.

Treatment includes antibiotics and surgery for lymph node removal in some cases. Hematopoietic stem cell transplantation (HSCT) may be considered in specific cases. Prognosis depends on the specific mutation and the associated disorder.