A Fresh Look at Whether the Human Appendix Should Be Considered “Friend or Foe” in the Context of Long-duration Remote Expeditionary Medicine (Benivolem aut Insidiator?)

Introduction:Traditional belief holds that the human appendix is a vestigial organ devoid of any purpose, and consequently, surgical appendectomy has been the “gold standard” treatment for suspected appendicitis. Prophylactic (preventative) appendectomy remains the policy of the Australian Antarctic Division for wintering medical practitioners and has been discussed in the context of long-duration non-orbital space flight.Aim:New research around appendiceal function, increasing adoption of non-surgical treatment modalities for acute appendicitis, and emerging research on the long-term consequences of appendicectomy have recently enabled researchers to challenge this paradigm.Methods:This novel project set out to test the hypothesis that a “one size fits all” prophylactic appendectomy policy may not be in the best interest of individual expeditioners, and utilized a “mindmap” to identify several key areas for a scoping literature review. This enabled disparate research to be drawn together in an innovative way.Results:A growing body of research has discovered that the appendix plays an important role in the gut immune system and maintaining gut health. It acts as a reservoir of good bacteria that repopulates the gut after pathogenic challenge. This is particularly important for people with impaired immune systems, such as those that occur in extreme environments. Appendicitis can often be successfully treated with intravenous antibiotics. Prophylactic appendectomy is not without risk, as 1:4 to 1:3 people will encounter some sort of postoperative complication. After an appendectomy, there is an increased risk of many serious medical conditions, including intra-abdominal adhesions, ischaemic heart disease, inflammatory and irritable bowel diseases, rheumatoid arthritis, and many others.Discussion:The increased morbidity and mortality associated with appendectomy is costly for individuals (the burden of disease) and society (health economics). It also poses a currently unappreciated health risk for long-term off-world expeditions.

The vermiform appendix impacts the risk of developing Parkinson’s disease

The pathogenesis of Parkinson’s disease (PD) involves the accumulation of aggregated α-synuclein, which has been suggested to begin in the gastrointestinal tract. Here, we determined the capacity of the appendix to modify PD risk and influence pathogenesis. In two independent epidemiological datasets, involving more than 1.6 million individuals and over 91 million person-years, we observed that removal of the appendix decades before PD onset was associated with a lower risk for PD, particularly for individuals living in rural areas, and delayed the age of PD onset. We also found that the healthy human appendix contained intraneuronal α-synuclein aggregates and an abundance of PD pathology–associated α-synuclein truncation products that are known to accumulate in Lewy bodies, the pathological hallmark of PD. Lysates of human appendix tissue induced the rapid cleavage and oligomerization of full-length recombinant α-synuclein. Together, we propose that the normal human appendix contains pathogenic forms of α-synuclein that affect the risk of developing PD.

Atypical localization of myenteric ganglia in the human appendical wall: a comparative study with animal appendix

The presence of well developed appendices in some animals when compared to humans has led to speculation that appendix is a vestigial organ. Increasing number of studies have revealed that the appendix serves as an important organ in humans. The function of animal appendix, and the differences between species remain poorly understood. In this study we examined human myenteric plexus and compared them with animal studies. Appendices were obtained from five young adults in which the appendix was found to be normal after removal. Fixed appendix cryosections were examined by immunofluorescence methods using neuronal marker antibodies to neurofilaments and beta III tubulin. Both antibodies stained myenteric ganglia which were arranged in an apparently irregular pattern in human appendix wall. We observed unexpected localization of myenteric ganglia in the subserosa often accompanied by rarely occurring ganglia in the longitudinal muscle layer. These ganglia were of different sizes and shapes and unequally distributed under a thin layer of serosa. Our findings raise many questions about the possible role of irregular and atypical myenteric ganglia localization in relation to altered motility and subsequent pathogenesis of the appendix in inflammatory disease in humans. On the other hand, studies of the literature have revealed simplicity in the organization of myenteric plexus, e.g., in well-developed rabbit appendix. In addition, appendicitis in animals is restricted to in apes with similarly shaped appendix to humans.

Microbial Composition of Human Appendices from Patients following Appendectomy

ABSTRACT The human appendix has historically been considered a vestige of evolutionary development with an unknown function. While limited data are available on the microbial composition of the appendix, it has been postulated that this organ could serve as a microbial reservoir for repopulating the gastrointestinal tract in times of necessity. We aimed to explore the microbial composition of the human appendix, using high-throughput sequencing of the 16S rRNA gene V4 region. Seven patients, 5 to 25 years of age, presenting with symptoms of acute appendicitis were included in this study. Results showed considerable diversity and interindividual variability among the microbial composition of the appendix samples. In general, however, Firmicutes was the dominant phylum, with the majority of additional sequences being assigned at various levels to Proteobacteria, Bacteroidetes, Actinobacteria, and Fusobacteria. Despite the large diversity in the microbiota found within the appendix, however, a few major families and genera were found to comprise the majority of the sequences present. Interestingly, also, certain taxa not generally associated with the human intestine, including the oral pathogens Gemella, Parvimonas, and Fusobacterium, were identified among the appendix samples. The prevalence of genera such as Fusobacterium could also be linked to the severity of inflammation of the organ. We conclude that the human appendix contains a robust and varied microbiota distinct from the microbiotas in other niches within the human microbiome. The microbial composition of the human appendix is subject to extreme variability and comprises a diversity of biota that may play an important, as-yet-unknown role in human health. IMPORTANCE There are currently limited data available on the microbial composition of the human appendix. It has been suggested, however, that it may serve as a “safe house” for commensal bacteria that can reinoculate the gut at need. The present study is the first comprehensive view of the microbial composition of the appendix as determined by high-throughput sequencing. We have determined that the human appendix contains a wealth of microbes, including members of 15 phyla. Important information regarding the associated bacterial diversity of the appendix which will help determine the role, if any, the appendix microbiota has in human health is presented.