Four orthopoxviruses cause infection in humans: variola, vaccinia, cowpox, and monkeypox. Variola infects only humans in nature, although primates and other animals have been infected in an experimental setting. Vaccinia, cowpox, and monkeypox viruses can infect both humans and other animals in nature.The life cycle of poxviruses is complicated by having multiple infectious forms, with differing mechanisms of cell entry. Poxviruses are unique among human DNA viruses in that they replicate in the cytoplasm of the cell rather than in the nucleus. To replicate, poxviruses produce a variety of specialized proteins not produced by other DNA viruses, the most important of which is a viral-associated DNA-dependent RNA polymerase. Both enveloped and unenveloped virions are infectious. The viral envelope is made of modified Golgi membranes containing viral-specific polypeptides, including hemagglutinin. Infection with either variola major or variola minor confers immunity against the other. Variola Major
The more common, infectious form of the virus comes from the Variola major strain. Variola minor
Variola minor, also called alastrim, was a less common form of the virus, and much less deadly. Although Variola minor had the same incubation period and pathogenetic stages as smallpox, it is believed to have had a mortality rate of less than 1%, as compared to smallpoxs 30%. Like Variola major, Variola minor was spread through inhalation of the virus in the air, which could occur through face-to-face contact or through fomites. Infection with Variola minor conferred immunity against the more dangerous variola major.
Pyomyositis is a bacterial infection of the skeletal muscles which results in an abscess. Pyomyositis is most common in tropical areas but can also occur in temperate zones. Diagnosis
Diagnosis is done via the following manner:
Pus discharge culture and sensitivity
X ray of the part to rule out osteomyelitis
Creatinine phosphokinase (more than 50,000 units)
MRI is useful
Ultrasound guided aspiration

Treatment
The abscesses within the muscle must be drained surgically (not all patient require surgery if there is no abscess). Antibiotics are given for a minimum of three weeks to clear the infection. Epidemiology
Pyomyositis is most often caused by the bacterium Staphylococcus aureus. The infection can affect any skeletal muscle, but most often infects the large muscle groups such as the quadriceps or gluteal muscles.Pyomyositis is mainly a disease of children and was first described by Scriba in 1885. Most patients are aged 2 to 5 years, but infection may occur in any age group. Infection often follows minor trauma and is more common in the tropics, where it accounts for 4% of all hospital admissions. In temperate countries such as the US, pyomyositis was a rare condition (accounting for 1 in 3000 pediatric admissions), but has become more common since the appearance of the USA300 strain of MRSA.Gonococcal pyomyositis is a rare infection caused by Neisseria gonorrhoeae. Additional images
References

Maravelas R, Melgar TA, Vos D, Lima N, Sadarangani S (2020). "Pyomyositis in the United States 2002-2014". J Infect. 80(5):497-503. doi:10.1016/j.jinf.2020.02.005. PMID 32147332. == External links ==