T. whipplei has been detected in various biological specimens of infected people, including saliva, urine, blood, heart valve, myocardium, synovial fluid, skeletal muscle, feces, skin, lymph nodes, lung, bronchoalveolar fluid, stomach, spleen, liver, larynx, small intestine, colon, maxillary sinus, cerebrospinal fluid, and aqueous humor.
T. whipplei can persist in vectors for several years, and asymptomatic carriers can become a large reservoir for infecting others [
2]. Whipple’s disease is mainly transmitted by the oral–oral or fecal–oral routes. A high prevalence of this disease was reported among people with poor quality health, sewage workers, and homeless people [
3,
4]. There are four forms of
T. whipplei infection in humans, including classic Whipple disease, chronic localized infection, acute infection, and asymptomatic form [
2]. The classic form of the Whipple disease is most common in men. Arthralgia, diarrhea, fatty diarrhea, loss of weight, lymphadenopathy, abdominal pain, hypoalbuminemia, and anemia are often observed as clinical symptoms of this form of Whipple's disease [
5]. All the organs, in particular the eyes, heart, and central nervous system can be involved at the end stage of the disease. Local infection with
T. whipplei is often without gastrointestinal involvement. However, it can be associated with encephalopathy, endocarditis, respiratory problems, lymphadenopathy, osteoarticular, and uveitis [
2]. Recently, it was reported that
T. whipplei caused acute infections, including gastroenteritis, bacteremia, or pneumonia [
1]. Although diarrhea is one of the symptoms of the chronic, classic, and acute forms of
T. whipplei infection, diagnosis is often difficult because there are no specific endoscopic findings, and this bacterium is not detectable by routine stool culture. The histopathology and PCR methods are the most well-known
T. whipplei diagnostic approaches [
6,
7]. However, histopathological examination of the biopsy specimen is not commonly used for screening purposes because it is a costly and invasive method. In contrast, PCR can be preferred to identify
T. whipplei in various specimens (e.g., stool, mucosa, and fluids), and it is a fast, specific, sensitive, and cost-effective method [
2]. In addition, transmission electron microscopy is a helpful diagnostic tool for identifying both living and dead bacteria after therapy, when available [
8]. Early diagnosis can help to treatment and eradication of
T. whipplei in patients. However, misdiagnosis or improper treatment, which especially occurs in patients without the classic symptoms, can lead to lethal outcomes or irreversible neurological damage. Sometimes, patients with early symptoms may also be hard to treat due to the presence of bacteria in an inaccessible niche for the antibiotic, antibiotic resistance, or reinfection in late relapses after antibiotic treatment. Where combination therapy with antibiotics is helpful, immunosuppressive treatment can be a risk factor for displaying or aggravating Whipple's disease [
2,
9,
10]. Diarrhea in children is a significant health threat in developing countries that is caused by various microorganisms. Recent studies in many countries have shown that
T. whipplei is one of the infectious causes of diarrhea in children. The results of these studies showed that the prevalence of
T. whipplei was more in the stool of children with diarrhea than healthy children as a control group. For instance, using the qPCR method, stool prevalence of
T.whipplei was 27.5% among children with diarrhea from Ghana. That case group carried
T.whipplei in their stool twice as frequently as controls without diarrhea [
11]. In another case–control study,
T. whipplei was identified in 15% of stool samples collected from children with gastroenteritis using the qPCR method. In addition,
T. whipplei antibody was reported in the case group. None of the control cases were positive for the presence of bacterium or antibody. Interestingly,
T. whipplei was not detected in the stool samples of children after recovering from diarrhea [
12]. Therefore,
T. whipplei should be considered as one of the potential causes of diarrhea in children. Since clinical symptoms are not sufficient for
T. whipplei diarrhea diagnostic, molecular tests are essential to confirm this disease. In Iran, similar to most countries of the world, there is no comprehensive survey on the prevalence of
T. whipplei, particularly in children with diarrhea. Therefore, the present study was performed to evaluate the presence of
T. whipplei in stool samples of children with acute diarrhea using molecular methods.