After a series of Covid-19 waves, several known infectious diseases are known to have appeared with unknown presentations or in more severe forms. Tomato flu, severe acute hepatitis of unknown origin in children, multisystem inflammatory syndrome in children, monkeypox virus and dengue virus are some of those diseases that appeared either with initially unknown etiology (as mysterious diseases) or in a more severe form after Covid-19. Could these unprecedented shifting presentations be a coincidence or an impact of Covid-19?

Some experts believe that Covid-19 may have damaged, caused long-term effects, or interfered with immunity system, contributing to the vulnerability to other infections. Effects of long Coivid have been widely seen worldwide, considered an unexpected sequelae of SARS-CoV-2 infection. Long Covid is defined as the continuation of the development of new symptoms three months after the initial SARS-CoV-2 infection, lasting at least two months with no other explanation. Long Covid-19 conditions are described as mainly associated with non-communicable diseases (sequelae), for instance, neuropsychiatric, endocrine, gastrointestinal-hepatobiliary, pulmonary, dermatologic, renal, cardiovascular, hematologic, and pulmonary problems. In contrast, communicable diseases (infectious diseases) have appeared either as mysterious (or with altered symptoms) diseases or in a more severe form, prompting challenges in early diagnosis and treatment.

On May 6, 2022, tomato flu drew the attention of healthcare workers in the Kollam district of Kerala, India. Children under nine years were more affected by the tomato flu. Fever, rashes (tomato-shaped red rashes and painful blisters) and joint pains were found to be the main symptoms among tomato flu-affected children. As mentioned in the journal Lancet Respiratory Medicine, the authors were unsure about the causative agent of tomato flu but assumed the possible introduction of a new viral infection. Later, however, it was identified as an enterovirus (CA16), the most common cause of hand, foot and mouth disease (HFMD).

In November 2022, I observed tomato flu-like illness in a 41-year-old male with no travel history to India. HFMD is a common childhood viral infection, but it showed unusual presentations in 2022, and it might be due to the impact of Covid-19. Likewise, acute severe hepatitis of unknown origin in children has been observed across the United Kingdom since the beginning of 2022. According to the World Health Organization (WHO), multiple countries have reported similar symptoms in children, with approximately 10 percent of the affected cases requiring liver transplantation. Surprisingly, adenovirus, previously known as a common cold virus, was detected in these affected children. Indeed, it was very unusual to detect adenovirus as a causative agent of acute severe hepatitis and liver failure in previously healthy children, and in a similar time period worldwide. It is worth mentioning that severe respiratory symptoms were observed in children due to adenovirus in mid-July 2022 in Nepal. Pediatricians noted severe symptoms of respiratory illness in children for a longer period than usual. Interestingly, however, there were no reports of severe acute hepatitis in children as seen in the United Kingdom and around the world during the adenovirus outbreak in Nepal.

Multisystem inflammatory syndrome is another unexpected health problem among children worldwide, including in Nepal. It is rare but is associated with the SARS-CoV-2 infection that causes inflammation in different body parts. Overall, severe or fatal Covid-19 were found significantly less common in children compared to adults during Covid-19 waves. Nevertheless, a series of infectious diseases with unusual (atypical) presentations have also been observed in children worldwide.

On May 25, 2022, the United Kingdom notified a laboratory-confirmed case of monkeypox virus (mpox) to the WHO. Mpox virus is transmitted person-to-person through close contact with lesions, bodily fluids, respiratory droplets and contaminated material such as bedding. Fever, rash and swollen lymph nodes are its typical clinical presentations, and its case fatality rate has been estimated to be around 1 to 10 percent. Interestingly, a study published in the New England Journal of Medicine showed that 95 percent of infected patients presented with skin lesions, mainly around the anogenital (73 percent) area. The most striking observation was that only 62 percent (nearly half) of the cases presented with fever and 56 percent with swollen lymph nodes, meaning mpox virus was/is presenting with symptoms differ from those in countries where mpox is endemic. Moreover, the study also showed that sexual contact was a strong likelihood of the primary mode of transmission of a recent mpox virus outbreak, meaning the 2022 mpox virus had appeared with shifting its characteristics with respect to its clinical presentations and transmission route, respectively.

In 2022, Nepal experienced the largest-ever outbreak of dengue fever, with the highest number of casualties due to its complications. It was observed soon after the series of Covid-19 waves. The majority of the patients with dengue virus who visited the hospital had a history of severe complications, such as bleeding and brief unconsciousness or shock. The reason for severe dengue disease and the increased fatality rate remains under investigation. Nonetheless, some experts believe that it might have happened due to a change in serotypes (i.e., the majority of patients were infected with serotype 3 in 2022; in the 2019 dengue outbreak, it was serotype 2). However, the impact of Covid-19 on the immunity system cannot be overlooked, although it warrants further investigation.

To conclude, several infectious diseases have appeared either as unexplained diseases or with atypical (or unusual) presentations following Covid-19 waves. Whether it is a mere coincidence or due to the effects of Covid-19 on the immunity system remains a matter of scientific debate.