Clinical Spectrum of Schistosomiasis: An Update

Schistosomiasis is a helminthic infection and one of the neglected tropical diseases (NTDs). It is caused by blood flukes of the genus Schistosoma. It is an important public health problem, particularly in poverty-stricken areas, especially those within the tropics and subtropics. It is estimated that at least 236 million people worldwide are infected, 90% of them in sub-Saharan Africa, and that this disease causes approximately 300,000 deaths annually. The clinical manifestations are varied and affect practically all organs. There are substantial differences in the clinical presentation, depending on the phase and clinical form of schistosomiasis in which it occurs. Schistosomiasis can remain undiagnosed for a long period of time, with secondary clinical lesion. Here, we review the clinical profile of schistosomiasis. This information may aid in the development of more efficacious treatments and improved disease prognosis.

Schistosomes in the Lung: Immunobiology and Opportunity

Schistosome infection is a major cause of global morbidity, particularly in sub-Saharan Africa. However, there is no effective vaccine for this major neglected tropical disease, and re-infection routinely occurs after chemotherapeutic treatment. Following invasion through the skin, larval schistosomula enter the circulatory system and migrate through the lung before maturing to adulthood in the mesenteric or urogenital vasculature. Eggs released from adult worms can become trapped in various tissues, with resultant inflammatory responses leading to hepato-splenic, intestinal, or urogenital disease – processes that have been extensively studied in recent years. In contrast, although lung pathology can occur in both the acute and chronic phases of schistosomiasis, the mechanisms underlying pulmonary disease are particularly poorly understood. In chronic infection, egg-mediated fibrosis and vascular destruction can lead to the formation of portosystemic shunts through which eggs can embolise to the lungs, where they can trigger granulomatous disease. Acute schistosomiasis, or Katayama syndrome, which is primarily evident in non-endemic individuals, occurs during pulmonary larval migration, maturation, and initial egg-production, often involving fever and a cough with an accompanying immune cell infiltrate into the lung. Importantly, lung migrating larvae are not just a cause of inflammation and pathology but are a key target for future vaccine design. However, vaccine efforts are hindered by a limited understanding of what constitutes a protective immune response to larvae. In this review, we explore the current understanding of pulmonary immune responses and inflammatory pathology in schistosomiasis, highlighting important unanswered questions and areas for future research.

New Insights on Acute and Chronic Schistosomiasis: Do We Need a Redefinition?

A precise timeframe to differentiate acute schistosomiasis (AS) and chronic schistosomiasis (CS) is not well defined. Based on recent published literature, lung nodular lesions in AS and CS seem to have the same pathophysiology, that is, eggs laid in situ by adult worms, during an ectopic migration. Moreover, the occurrence of lung nodules due to clusters of eggs and the systemic immunoallergic reaction of AS (Katayama syndrome) may be two separate clinical entities, which may overlap during the early phase of infection. Consequently, the classical distinction between AS and CS loses much of its conceptual validity. If adult worms play a more important role in the early phase of the disease the clinical management of AS should probably be revised.

Katayama syndrome disguised as eosinophilic asthma with acute systemic symptoms and pulmonary nodules

Background

Katayama syndrome is an acute manifestation of schistosomiasis, a parasitic infection that manifests itself through a hypersensitivity reaction to migrating larvae and early egg deposition. Left undiagnosed and untreated, acute schistosomiasis can develop into chronic schistosomiasis which can lead to debilitating morbidity such as pulmonary hypertension. This case highlights that Katayama syndrome can also been seen in regions where the parasite is not endemic, as it occurs in travelers returning from endemic regions or in immigrants.

Case presentation

We describe the case of a 26-year-old asthmatic male, who presented with systemic symptoms including fever, myalgia, night sweats as well as gastro-intestinal and pulmonary complaints since five days. At presentation, there was a raised blood eosinophil count and nodular lesions were seen on computed tomography. After considering diagnoses such as tuberculosis, vasculitis and hypereosinophilic syndrome, it was repeated history taking that revealed that the patient had suffered from swimmer's itch during a stay in Guinea. A stool sample showed microscopic presence of Schistosoma mansoni eggs, confirming the diagnosis of Katayama syndrome. The patient was treated with tapered corticosteroids to suppress the hypersensitivity reaction and praziquantel was added to cure the parasitic infection. This led to a complete resolution of the patients' symptoms and radiological abnormalities. Negative stool samples confirmed the eradication of the schistosomes.

Conclusions

Swimmer's itch and Katayama syndrome are manifestations of acute schistosomiasis. It is important to recognize the syndrome, because early diagnosis and adequate treatment can prevent chronic disease and significant morbidity.

Protracted Katayama syndrome in an immunocompromised traveller: the challenge of assessing cure

We describe a case of prolonged Katayama syndrome in an immunocompromised traveller. We highlight the difficulty of evaluating a cure due to persistent polymerase chain reaction (PCR) positivity and fluctuating markers. We discuss limitations of current diagnostic assays and advocate for improved access to reliable markers like the circulating anodic antigen test.