Infectious disease

Host genetic factors[edit]
The organism that is the target of an infecting action of a specific infectious agent is called the host. The host harbouring an agent that is in a mature or sexually active stage phase is called the definitive host. The intermediate host comes in contact during the larvae stage. A host can be anything living and can attain to asexual and sexual reproduction.^[69] The clearance of the pathogens, either treatment-induced or spontaneous, it can be influenced by the genetic variants carried by the individual patients. For instance, for genotype 1 hepatitis C treated with Pegylated interferon-alpha-2a or Pegylated interferon-alpha-2b (brand names Pegasys or PEG-Intron) combined with ribavirin, it has been shown that genetic polymorphisms near the human IL28B gene, encoding interferon lambda 3, are associated with significant differences in the treatment-induced clearance of the virus. This finding, originally reported in Nature,^[70] showed that genotype 1 hepatitis C patients carrying certain genetic variant alleles near the IL28B gene are more possibly to achieve sustained virological response after the treatment than others. Later report from Nature^[71] demonstrated that the same genetic variants are also associated with the natural clearance of the genotype 1 hepatitis C virus.
Treatments[edit]
When infection attacks the body, anti-infective drugs can suppress the infection. Several broad types of anti-infective drugs exist, depending on the type of organism targeted; they include antibacterial (antibiotic; including antitubercular), antiviral, antifungal and antiparasitic (including antiprotozoal and antihelminthic) agents. Depending on the severity and the type of infection, the antibiotic may be given by mouth or by injection, or may be applied topically. Severe infections of the brain are usually treated with intravenous antibiotics. Sometimes, multiple antibiotics are used in case there is resistance to one antibiotic. Antibiotics only work for bacteria and do not affect viruses. Antibiotics work by slowing down the multiplication of bacteria or killing the bacteria. The most common classes of antibiotics used in medicine include penicillin, cephalosporins, aminoglycosides, macrolides, quinolones and tetracyclines.^[72][73]
Not all infections require treatment, and for many self-limiting infections the treatment may cause more side-effects than benefits. Antimicrobial stewardship is the concept that healthcare providers should treat an infection with an antimicrobial that specifically works well for the target pathogen for the shortest amount of time and to only treat when there is a known or highly suspected pathogen that will respond to the medication.^[74]
Epidemiology[edit]

Deaths due to infectious and parasitic diseases per million persons in 2012
28–81
82–114
115–171
172–212
213–283
284–516
517–1,193
1,194–2,476
2,477–3,954
3,955–6,812
See also: Epidemic and Pandemic

Disability-adjusted life year for infectious and parasitic diseases per 100,000 inhabitants in 2004.^[75]
no data
≤250
250–500
500–1000
1000–2000
2000–3000
3000–4000
4000–5000
5000–6250
6250–12,500
12,500–25,000
25,000–50,000
≥50,000
In 2010, about 10 million people died of infectious diseases.^[76]
The World Health Organization collects information on global deaths by International Classification of Disease (ICD) code categories. The following table lists the top infectious disease by number of deaths in 2002. 1993 data is included for comparison.