**4. Clinical features of human brucellosis**

Although brucellosis in humans can affect people of any age, it most commonly affects men in their twenties and forties because of the more exposure to occupational risk [28].

Each species of *Brucella* is a facultative intracellular pathogen, meaning that it can live and reproduce within the host cell's phagocytic immune system. Still the ways by which Brucella evades intracellular death are poorly understood. But in the end, *Brucella* organisms are contained within RES monocytes and macrophages in organs including the lymph nodes, liver, spleen, and bone marrow [29]. Brucellosis is a systemic disease that can infect all the organs or tissues of the body. After Brucella enters the body, it goes through three distinct phases: the incubation period, the acute phase, and the chronic phase. The incubation period can vary from five days to five months and is not always straightforward to estimate. However, it is typically two to

four weeks. About half of all cases of the disease have an abrupt beginning within days to weeks after infection, whereas the other half have a more gradual onset within weeks to months following the initial infection. Clinical symptoms might be rather general and diverse. Symptoms may include high body temperature, sweating, weariness, general malaise, lack of appetite, weight, headache, aching joints, and pain in the back. Patients typically improve first thing in the morning and then experience a worsening of their symptoms throughout the day [30].

Fatigue, fever, sweating, splenomegaly, and hepatomegaly are all symptoms and signs that may appear during the acute phase.

Brucella possesses a wide variety of virulence characteristics that allow it to establish persistent infection by hiding within host cells and evading the immune system. Because of the high degree of clinical polymorphism, brucellosis is often missed at the first point of care [31].

Additionally, brucellosis is known to induce serious clinical problems involving the internal organs such as meningitis, encephalitis, arthritis, spondylitis, endocarditis, prostatitis, and orchitis [31].

The need for sleep might be overwhelming and sadness is common. The fever will fluctuate in intensity over the course of several days ("intermittent fever") if it is left untreated.
