A study on the role of lepidopterism in seasonal fever outbreaks.

UNLABELLED

Fever is one of the most common reasons for visit in primary care practice. Outbreaks of fever that occur at certain areas in a seasonal manner are usually recognized early by diligent general practitioners in primary care settings. At the community level, in order to tackle seasonal fever outbreaks, prevention and control strategies are widely implemented, targeting the locally prevalent endemic infectious diseases. However, what about seasonal outbreaks of diseases because of non-infectious endemic causes? How well are we aware of this and how prepared are we? In 2006, there was an outbreak of Chikungunya fever in Kerala, a southern state in India. A group of scientists discovered that many patients assumed to have Chikungunya also had exposure to a specific type of lepidopteran moth, , also known as tiger moth. Further research revealed that rats exposed to live tiger moths under experimental conditions produced features resembling Chikungunya and similar viral fevers, with symptoms comprising fever, arthralgia, arthritis, and thrombocytopenia. A moth-toxin-specific immunoglobulin E (IgE) antibody was identified in sera of patients who recalled exposure to tiger moths.

AIMS

1. To screen subjects with clinical features resembling viral fevers for specific IgE antibodies against tiger moth toxin. 2. To assess the role of tiger moths in producing features resembling viral fevers in humans.

SETTINGS AND DESIGN

This hospital-based, cross-sectional analytical study was conducted from March 2015 to March 2016 in a tertiary hospital in North Kerala. The sample population included patients who had clinical manifestations suggestive of viral fevers and presented to the outpatient departments of Family Medicine, Internal Medicine, or Emergency Medicine and satisfied the inclusion criteria.

METHODS AND MATERIAL

After collecting the informed consent, the blood sample needed for the study was collected simultaneously with the blood collected for other tests ordered by the consulting doctor. No extra needle insertion was needed for the study. A total of 234 samples were examined for the presence of moth-toxin-specific IgE antibodies.

STATISTICAL ANALYSIS USED

Data were analysed using SPSS 17.0. Graphs were produced using Microsoft Excel. Categorical variables were expressed as frequencies with percentages and analysed using Chi-square test/Fisher's exact test. Incidence/prevalence was also expressed in percentages with confidence interval. The continuous variable was expressed as mean with standard deviation or median with inter-quartile range. For all tests, a probability value (p value) < 0.05 was considered as statistically significant.

RESULTS

Among the 234 subjects who were screened in the 13-month period, 44 subjects (18.8%) tested positive for moth-toxin IgE, of which 28 were males and 16 were females. The maximum percentage of samples with positive moth-toxin IgE antibodies was detected during the months of March, June, July, November, December, and January. Out of the 44 subjects who had positive moth-toxin IgE antibodies, 24 tested positive for Dengue fever (of which eight were positive for the Dengue NS1 antigen, 11 were positive for the Dengue IgM antibody, and five were positive for both Dengue NS1 antigen and Dengue IgM antibody), two tested positive for Leptospira IgM antibody, two tested positive for Rickettsial antibody, and three had a positive Widal test. It was found that association of moth-toxin IgE with all the presenting symptoms of subjects analysed in this study was not statistically significant, except for lymphadenopathy. Skin rashes of different morphologies were seen in the study group. 20.5% (n = 9) of the subjects who tested positive for moth-toxin IgE had skin rashes. A majority of these weffigurere erythematous and maculopapular rashes, with incidence of 44% (n = 4) and 33% (n = 3), respectively.

CONCLUSIONS

1. A seasonal variation is evident in the incidence of cases with positive moth-toxin IgE. 2. There is no significant age/sex preference for moth-toxin IgE positivity. 3. Subjects who tested positive for moth-toxin IgE also had positive serological tests for other infectious causes of fever, including Dengue fever, Leptospirosis, Enteric fever, and Rickettsial fever. The role of tiger moth exposure in producing fever and related symptoms hence needs to be studied further. 4. It was observed that moth-toxin IgE had significant association with lymphadenopathy. This should be investigated in further studies. 5. Even though the role of lepidopterism in seasonal fever epidemics is not clear, primary care physicians should be more aware of such entities which can present with a wide range of manifestations.