To develop strategies for relieving and preventing the suffering of filarial patients, it is essential to understand the epidemiology of various forms of morbidity. The information on acute form of LF, particularly on ADL is sporadic from a few endemic regions. The present longitudinal prospective surveillance showed the annual incidence of 85.03 of ADL episodes per 1000 population in this rural Eastern Indian community. Similarly, a South Indian rural community, which is endemic for bancroftian filariasis recorded the annual incidence of 96.3 per 1000 population [
6]. The incidence rates are available from a few other endemic countries such as Ghana (96 per 1000 population) [
5] and Tanzania (33 per 1000 population) [
8]. The proportion of people affected with ADL episodes in the present study (5.4%) is similar to that reported from another bancroftian filarial endemic community from South India (5.3%) [
6]. The age wise distribution indicates that male recorded higher incidence in all age groups except in the age groups of 41–50 years and above 60 years of age. This age-wise incidence follows the pattern with the prevalence of microfilaraemia and chronic disease [
13]. The variation could be due to differences in prevalence of chronic disease and differential susceptibility to ADL episodes for individuals with lymphoedema and hydrocele. In the present population, men recorded higher prevalence of chronic filarial disease than women [
10]. The mean age of affected individuals is varying between male and female. The lower mean age of male patients may be due to occurrence of hydrocele even at lower age. In the present study population, majority of affected individuals has only one episode per year and only 27.8% of affected individuals have experience more than once. The data showed that these multiple episodes are more common in patients with chronic disease. The mean number of episodes per year is significantly higher among lymphoedema patients than even hydrocele patients. A study from South India reported a direct relationship between the number of acute attacks and the grade of lymphoedema [
14]. It is also known that the frequency of these attacks is generally higher in bancroftian filariasis as compared to brugian filariasis [
14,
15]. Regarding the seasonal variation in the frequency of ADL episodes, it is lower in winter than is summer and rainy season. Some of the earlier studies reported higher frequency in rainy season [
16,
17]. In Tanzania, the higher incidence of ADL episodes during rainy season is related to increased transmission by infective mosquito bites [
8]. It is consistent with the hypothesis that ADL episodes may be associated with allergic responses to massive parasite antigen release [
18,
19]. There is uniformity in the associated symptoms of ADL episodes amongst various endemic communities, though the etiology of the ADL is not clear. The majority of the ADL patients in this study are amicrofilaraemic, and this finding is in conformity with earlier observations [
5,
19,
20]. The limitation of this study is that an insensitive method of microfilaria detection was used, i.e., finger prick method as opposed to Nucleopore filtration method.
The incidence and duration of the ADL episode has greater economic implication on individuals, their families and community. There will be substantial loss of work during these episodes and subsequent economic loss [
21‐
23]. In the present study population, on average each episode persists for 4 days, which is similar to the other endemic areas [
6,
8,
16,
24,
25]. The magnitude of loss due to ADL episodes is substantial and it will be constituted as a major proportion to the total burden of LF. While estimating the global burden of LF, only the chronic forms of disease were considered [
26], perhaps due to lack of data at that time. As the data on incidence and duration of ADL episodes are available at least from some endemic areas, they should be considered during further estimation of disease burden due to LF. In the present study community, it is reported that the chronic condition is posing considering economic burden due to loss of work and treatment costs [
27]. It is well known that the disability and economic loss caused by chronic filariasis is life long and much higher. And additional incapacity caused by the ADL episodes, majority of which occur in these chronic filarial patients, further poses the burden on the individuals and their families. It is clear that there are two types of ADL episodes, ADL secondary to bacterial or fungal infections and ADL caused directly by the parasite infection itself [
1]. For the episodes among chronic lymphoedema cases, secondary bacterial infection may be plausible explanation [
28‐
30]. It is also evident from recent findings that simple foot hygiene and prevention of secondary bacterial infection lower the incidence of ADL episodes [
28,
31‐
33]. Shenoy et al. [
34] demonstrated that well designed programme of foot care significantly decreases the frequency of ADL episodes. In this programme, meticulous hygiene including use of foot wear, regular washing of affected limbs, etc. to prevent injuries and infections needs to be incorporated. Thus, it is essential to develop and promote simple, cost-effective and user-friendly measures to minimise the burden of acute disease of LF.