We retrospectively analyzed pathological evidence from 120 children aged < 18 years who underwent appendectomy, which confirmed the relationship between adenovirus infection and appendicitis through IHC and qPCR analyses.
Adenoviruses are important human pathogens associated with a wide range of clinical diseases. Among these, the association between adenovirus infections and intussusception has been well documented (6). For example, a team from our hospital showed this relation by analyzing the annual incidences of both conditions from January 2008 to June 2011, showing a similarity in peak months for both (4). Another study showed simultaneous intussusception and adenovirus infection in monozygotic twins (2).
In addition to intussusception, adenoviruses can induce appendicitis. Adenoviruses of different serotypes can cause both intussusception (species C serotypes 1, 2, 5, and 6) and acute appendicitis (species B, mainly serotypes 3, 7, 11, 14, 21, and species E serotype 4) (1, 7). The cause of appendicitis is usually obstruction of the appendiceal lumen, resulting in progressively increased intraluminal pressure and subsequent venous congestion that leads to progressive inflammatory changes and ischemia. Most hypotheses about the mechanism of appendicitis rely on the concept of appendix blockage. Although this seems reasonable, experimental evidence suggests that the role of feces as an etiology of appendicitis is limited (8). Obstruction occurs in 50–80% of appendicitis cases and, in children, is most often due to fecaliths or lymphoid hyperplasia. However, the most common cause of lymphoid hyperplasia is catarrhal inflammation secondary to viral infection.
The incidence of acute appendicitis is estimated at 75 per 100,000 per year, with the highest rate among children aged 10–19 years. Overall, 67% of cases are nonperforated (9). Historically, the cause of appendicitis has been believed to be feces blocking the lumen. However, our experience has been that a bezoar is not always present, which we were able to show in approximately 50% of patients. Lynch et al. also noted that adenovirus-associated acute appendicitis is underrecognized (7).
Regarding the relationship between lymphoid hyperplasia and appendicitis, the general theory is that lymphoid hyperplasia may lead to appendix obstruction, followed by suppurative appendicitis. The concept of lymphoid hyperplasia associated with appendicitis is not new and numerous reports have dealt directly or indirectly with the topic (10–13). A recent article by
Sheridan et al. focused on this issue (14) and confirmed our study of appendicitis without fecalith (15, 16). Further, the United States (US) Food and
Drug Administration approved an adenovirus vaccine in 2011 (only available to US military personnel aged 17–50 years), the indication of which is prevention of febrile acute respiratory diseases caused by adenovirus types 4 and 7, and indirectly to reduce the occurrence of appendicitis (7).
Spectrophotometry can be used to measure microgram quantities of pure DNA samples (i.e., DNA uncontaminated by proteins, phenol, agarose, or RNA). Fluorescence is more sensitive and can measure DNA in nanogram quantities. Absorbance readings can be used to determine sample concentration and calculate the A260/A280 ratio to indicate sample purity. It is generally accepted that relatively pure DNA will yield an A260/A280 ratio ≥1.8 (17). All samples herein met this standard.
IHC plays an important role in diagnosis of infectious diseases in tissue samples. IHC using monoclonal and polyclonal antibodies is useful for detecting pathogen antigens in fixed tissues, complementing the direct diagnosis of infectious diseases by fresh tissue PCR and culture (18). While conventional PCR assays have been described for adenoviruses based on hexon and fiber gene sequences, these are labor intensive due to the need for post-PCR product analysis by gel electrophoresis and confirmatory hybridization assays or sequencing (19). Our findings also support qPCR assay for sensitive and specific detection of adenoviruses.
To our knowledge, this is the first report of adenovirus infection clinically manifesting as acute appendicitis without intussusception in Taiwan. Here, we combined the results of IHC and qPCR to show that the adenovirus detected in this study was species B serotype 3 (5). Our study confirmed that adenovirus can infect the appendix, presenting as acute symptoms and signs of appendicitis. We hypothesize that adenoviruses may play a causative role in some acute appendicitis cases. Future experiments will be needed to examine appendicitis cases for the presence of infectious agents as potential mechanisms.
Limitations
A second pathologist’s interpretation of samples was not included. Finally, interpreting Cq ≤40 as positive may require some adjustment.