Impact of Monsoon on the Pattern of Infectious Diseases in the Indian Setting- A Review

1. Professor, Department of Microbiology, Mahatma Gandhi Medical College and Research Institute, Puducherry, India. 2. Professor, Department of Microbiology, Mahatma Gandhi Medical College and Research Institute, Puducherry, India. 3. Professor, Department of Microbiology, Indira Gandhi Institute of Dental Sciences, Puducherry, India.

Abstract

The survival of life on earth depends on equilibrium between the organisms and the environment. The monsoon is a seasonal variation prevailing in the Indian sub-continent. Monsoon has two seasons which are separated by a transition. The infectious diseases epidemiology is affected by both climatic and societal influences. An interaction of climatic and societal influence favours the infectious disease exposure in a population. The infectious diseases affecting the population can be broadly classified as vector borne diseases, food borne diseases, water borne diseases, and respiratory diseases. The rainfall associated change in temperature and floods favours the survival of infectious diseases and their transmitting vectors. The changing global climatic trends including the EL nino Southern oscillation bring undue rainfall during other seasons. The drastic events associated with these climatic changes affect the health and sanitation infrastructure. India being a developing country has more vulnerability to such infections. A better strengthening of the infrastructure and health policies is the need of the hour to curb the infections.

Climate change, Elevated temperature, Environment, Food borne disease, Infectious agents, Rainy season, Vector borne disease, Water borne disease

The evolution of mankind and its survival on the globe is based on the interaction between the diversified biomes, including microbes, animals, and the climatic influence. The ecological equilibrium attained between these organisms and environment claims the survival of life on earth. However, the Anthropocene epoch which is a unique modification created by human on the environment and climate has deranging effects on health and disease (1). The urbanisation and domestication have a direct influence on infectious diseases in this regard (2). The pathogen and its interaction with the host are also driven by the climatic variation and associated geographical events along with the other factors (3). The average global temperature has increased by 0.85°C due to the greenhouse effect (4). The associated climate change alters the ecology of the pathogens and their vectors which raises the infectious disease spread. As per the World Health Organisation (WHO) report, around 12.6 million mortality are estimated in relation with climate change and pollution (5). The monsoon is a seasonal variation prevailing in the Indian sub-continent. It has two seasons which are separated by a transition. The South-West monsoon is from June to September and the North-East monsoon is from December-March. This brings highest rainfall to the western states, (Maharashtra, Goa, Karnataka, and Kerala) and eastern states (Arunachal Pradesh, Assam, Manipur, Mizoram, Tripura, and Meghalaya). Moderate rainfall in the Southern-East states of Tamil Nadu, Andhra Pradesh, Telangana, and Puducherry. During this period, the changing wind current, decrease in temperature, and rainfall affect various ecological niches promoting infections. The geographic location of the sub-continent which is surrounded by the ocean in all direction makes it vulnerable to unpredictable events such as cyclone and flood (6). In addition, the EL nino Southern oscillation drastically affects the seasonal cycle bringing heavy rain during summer. These unforeseen seasonal events predispose to water borne, vector borne, food borne, zoonotic, and respiratory diseases. There are very few data on the climate change and the infectious disease pattern. Hence, the aim of the review is to discuss the common infectious agents which affect humans during the monsoon.

RISK FACTORS PREDISPOSING INFECTIOUS DISEASE

The infectious disease epidemiology is affected by both climatic and societal influences. The climatic modifications such as precipitation, flood, temperature extremes, and drought affect the infectious disease epidemiology (7). Furthermore, the societal influences such as geographic location, socio-economic status, demography, and general health condition predispose the infectious diseases (8). An interaction of climatic and societal influences favours the infectious disease exposure in a population.

Climatic Factors

Precipitation and flooding: The flood and extreme precipitation damage the water infrastructure available. The flood water can damage the good water supply and breach the sanitation infrastructure. In addition, population movement and lack of sanitation measures can lead to infectious diseases. The stagnant water becomes the potential source of mosquito breeding. The rising sea level can affect the drinking water supply. The salinity of the intruding sea water can affect the soil and water quality [7,8]. In addition, the infrastructure of transportation, airport, harbour, telecommunication, agriculture, and electricity generation may be affected.

Drought: During drought the scarcity of water damages the livelihood of both human, plants and animals. The agricultural failure and undernutrition predispose to infections. The alternative water sources have high chance of contamination and pathogens could be concentrated in these areas. The limited contaminated water sources could be exchanged between human and livestock leading to infection (7). The cross contamination of water lines and vector breeding on the limited household water could be added disadvantage.

Elevated temperature: The higher temperature reduces the water resources available for human use. The vector borne diseases have higher chance of transmission. The extrinsic incubation of the pathogen and replication is favoured. The marine and animal pathogens are highly prevalent due to higher multiplication rates (8). These pathogens could be easily transmitted at the recreational sites. The reduced crop yield and food spoilage are the other factors.

Societal Factors

Geographic location and socio-economic status: The geographic location can predispose the population to infectious diseases. The location near a flood risk zone, cyclone risk zone and drought risk zones make the population prone to infection (7). Similarly, the population with poor socio-economic status and poverty are affected by these infections. The reduced health care access, unsafe water, poor sanitation, inadequate shelter, and lack of education are other socio-economic determinants.

Demography: The extremes of age including the neonates and senior citizens are highly prone for infection. Similarly, the prevalence of infectious disease varies with gender. Women are more prone for certain infections compared to men and vice versa. The movement of population to other areas can spread the infectious disease to other population group (7).

General health condition: The general well-being of the population decides their vulnerability to infection. The malnourished or undernourished population is widely affected by infections. The pregnant women, breast feeding women, immunocompromised individuals, and those with chronic diseases are prone for infectious disease (7).

INFECTIOUS DISEASES IN MONSOON

The infectious diseases affecting the population can be broadly classified as vector borne diseases, food borne diseases, water borne diseases, and respiratory diseases (9). The disease under each category is shown in (Table/Fig 1).

1. Vector Borne Diseases

The altered climatic conditions have a direct and indirect influence on the vector population. It can modify the reproduction rate of vector, increase its biting rate as well as reduce the incubation period of the pathogen (10). In addition, the societal factors decide the susceptibility of the host to infection. The common vectors transmitting infection are mosquitoes, ticks, and sand fly.

1.1 Mosquito Borne Diseases

Malaria: Malaria is caused by the protozoan parasite comprising of five common species Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, Plasmodium malariae, and Plasmodium knowelsi which are transmitted by the bite of the female anopheles mosquito. The major malaria vector in India is Anopheles stephensi, Anopheles fluviatilis, Anopheles sundaicus, Anopheles minimus and Anopheles dirus (11). Malaria is endemic in Odisha, Chhattisgarh, Jharkhand, Meghalaya, and Madhya Pradesh. The temperature, precipitation and humidity are the climatic factors which influence transmission of the disease (12). The dynamics of infection rate depends on the sporogony or extrinsic incubation period which is related to the environmental temperature. The optimal temperature range for development of P. falciparum is 19°C and P. vivax is 15°C. However, malaria cases are not observed to have a direct relationship with the annual rainfall (13). It is proposed that the wetness prevailing after the rainfall favours the multiplication of the Plasmodium spp. The 2mosquito survives in the relative humidity of 55-80% failing which transmission fails. However, a perineal conducive climate prevails throughout the country favouring the prevalence of positive cases (14). Malaria is reported with annual incidence of 146559 cases in the year 2021 (15).

Dengue: Dengue is an arboviral disease of tropical and sub-tropical countries. It is caused by the dengue virus comprising of five serotypes (DENV1-5) belonging to the flaviviridiae family. It is transmitted by two major vectors Aedes aegypti and Aedes albopictus in India (16). The epidemics of the disease have spread across various states (Orissa, Arunachal Pradesh, Mizoram) of the country since its identification (17). It is found that, a strong association exists between the precipitation and the mosquito breeding. It is found that, mosquitoes have better expansion of their spatial range in wet climate (18). In a study conducted by Nair DG et al., comparison of rainfall with dengue cases reveals a strong association. It is found that the dengue cases rise during the monsoon and reduce during the postmonsoon (19). An increase of rainfall greater than 1 mm per day to 10 mm shows strong association. However, it is also reported that the transmission intensity also depends on the warm temperature and high humidity which shortens the extrinsic incubation period and the feeding intervals (20). Dengue is reported with annual incidence of 110437 cases in the year 2022 (15). Among the premonsoon, monsoon, postmonsoon and winter seasons of the Indian sub-continent, Kerala shows lowest extrinsic incubation period (8-12.5 days) during monsoon, Gujarat shows extrinsic incubation period of 5-13.5 days, Rajasthan 3-12.6 days, Haryana 4-14.68 days and Punjab 5-22.7 days (21).

Chikungunya: In 1952 the first case of Chikungunya virus infection was identified in Tanzania. Among the several serogroups of alphavirus (Togaviridae family) Chikungunya virus belongs to the Selmiki forest antigenic complex (22). Aedes aegypti and Aedes albopictus is the two major vector which transmit the infection (23). The average temperature range for propagation of the same ranges from 20-30°C (24). In a study conducted from years 2010-2014 showed that, there is a strong association between rainfall and incidence of chikungunya cases. During 2017 outbreaks in the region of Tamil Nadu (131 cases) and Kerala (78 cases) were during the monsoon period with heavy rainfall (25). The recent estimate in the year 2022 shows annual incidence of 108957 cases (15).

West Nile fever: West Nile fever is caused by the West Nile Virus (WNV) belonging to the faviviridae family. The virus was first isolated from West Nile district in Uganda during 1937 (26). The virus circulates among human, horses, and mosquitoes. The natural or enzootic cycle exists between birds and mosquitoes. Human and horses are the dead-end host. The Culex vishnui mosquitoes are the vectors for the virus in India. The Aedes albopictus mosquito act as a bridging vector. The virus has also been isolated from frugivorous bats and domestic pigs in India. Heavy rainfall followed by dry temperature facilitates the vector breeding and disease spread (27). WNV has been isolated sporadically from parts of Tamil Nadu and Bombay. In 1952 the first case was identified in Bombay followed by other cases from Vellore and Kolar (28).

1.2 Tick Borne Diseases

Tick borne viral infections including Crimean Congo Haemorrhagic Fever (CCHF), Kyasanur Forest Disease (KFD), tick typhus and Lyme disease have been reported from the Indian Sub-continent (29). CCHF is transmitted by the ixodid tick belonging to the genus Hayalomma. Outbreaks of CCHF have been reported from Gujarat, Rajasthan, and Uttar Pradesh (30). Similarly, KFD caused by bite of Haemaphysalis spinigera ticks is reported from Karnataka, Kerala, Goa, Maharashtra, and Tamil Nadu. The tick typhus (etiological agent: Rickettsia conori) is transmitted by Rhipicephalus sanguineus ticks whereas, Lyme disease (etiological agent: Borrelia burgdorferi) is transmitted by Ixodes ticks. Lyme disease is increasingly reported from Indian states (31). The prevalence of these tick-borne diseases could be affected by vector range, pathogen prevalence, transmission dynamics, and climatic impact. However, studies are lacking on the association of precipitation and these tick-borne infections.

1.3 Mite Borne Infection

Scrub typhus is caused by Orientia tsutsugamushi which is transmitted by the trombiculid mite. It is the leading cause of acute febrile illness prevalent in most parts of the country. However, the disease in under-reported compared to the global rate of incidence (32). The scrub typhus infections are mostly reported during the premonsoon and postmonsoon season though there is evidence of perineal transmission (33). In a study conducted from 2012-2015 around 41.3% of scrub typhus cases were reported from Pondicherry. Similarly, 16.1% cases were reported from Tamil Nadu during 2004-2005 (34).

1.4 Sand Fly Borne

Leishmaniasis is caused by the protozoan parasite Leishmania donovani which is transmitted by the sand fly (Phlebotomus argentipus). The disease is endemic in states of Bihar, West Bengal, Uttar Pradesh, Jharkhand, Delhi, Gujarat, Madhya Pradesh and Kerala. The annual incidence reported during 2022 in these states are 490 cases in Bihar, 166 cases in Jharkhand, 18 cases in Uttar Pradesh, and 40 cases in West Bengal (15). The chronic Visceral leishmaniasis or Kala azar causes 50% mortality among the infected in the Indian sub-continent (35). The vector stays in the places where humidity and temperature are prevalent at regular intervals such as tree holes, crevices, dung and domestic waste. The changing climatic conditions such as rainfall, rise in temperature, and humidity have a direct effect on the vector population. It increases their survival and distribution thereby spread to newer areas which are non endemic. The migration of the population during monsoon and flood also predispose to infection (36).

2. Food Borne Infections

Enteric fever: Enteric fever is a febrile illness caused by Salmonella enterica serovar Typhi, Salmonella enterica serovar Paratyphi A, B, C. The estimated global incidence of the infection ranges from 6.9-48.4 million (37). The common mode of transmission of enteric fever is via ingestion of contaminated food and water (38). The associated co-factors include the host behaviour, and environmental factors predisposed by the seasonal dynamics (39). It is shown that the prevalence of infection increases with higher temperature, rainfall, and water stagnation (40). In a systematic review conducted by Saad NJ et al., it is found that the peak incidence of enteric fever was from May-October in most of the Asian countries (41). It is found that there is a strong association of peak incidence following the monsoon. The reason being the floods postmonsoon which contaminate the drinking water sources causing infection (42). The estimate of annual incidence of enteric fever in the year 2022 is around 4.5 million cases (43). The high incidence was reported in Maharashtra, Tamil Nadu, Delhi, and Chandigarh whereas, lower incidence was reported in Arunachal Pradesh and Himachal Pradesh (44). The data on incidence of various diseases during the last 5 years has been presented in (Table/Fig 2) (15),(44).

Campylobacteriosis: It is a zoonotic infection transmitted from domestic animals and birds. It is caused by Campylobater jejuni and Campylobacter coli. The gastroenteritis caused by Campylobacter spp is following consumption of infected chicken, raw, milk, and contaminated water. The incidence of this infection is reported among 10% of diarrhoea cases (45). In a study conducted in India, around 71.87% of paediatric Campylobacter cases were isolated both during summer and monsoon months (46). Similarly, study conducted in animals had shown a peak incidence of infection during the summer (57%) followed by the South-West monsoon season (26.2%) (47). Campylobacteriosis among human is reported from states of Tamil Nadu, Chandigarh, Maharashtra, and Karnataka (45).

Botulism: Food borne botulism is caused by anaerobic spore forming rod shaped bacilli Clostridium botulinum. The botulinum toxin inhibits the acetyl choline release from synaptic vesicles at the neuromuscular junction. The spore of the organism is present in contaminated soils, algae, plants, and invertebrates (48). The spores are also present in freshwater sediments of lake, river, and wetlands. Heavy rain and wind are important predisposing factors which mobilise the spores causing human infection. The association of botulism and monsoon needs to be studied in the Indian settings.

Hepatitis: Hepatitis A and E are the viruses which are transmitted by contaminated food and water. The viral hepatitis surveillance data conducted in India from 2011-2013 shows incidence of 7.4% for Hepatitis A and 10.4% for Hepatitis E (49). Most of these cases were from rural areas and contaminated drinking water had association with most outbreaks. A peak in the cases (17%) was seen from June-September denoting the association with rainfall and contamination of drinking water (49). In a study conducted from central India (2015-2017), 31.4% acute hepatitis cases were reported. Around 29% cases were Hepatitis E, and 5.1% cases were Hepatitis A (50). Both virus outbreaks are reported from states of Uttar Pradesh, West Bengal, and Gujarat.

3. Water Borne Diseases

Cholera: Cholera is a diarrhoeal disease caused by the Gram-negative bacilli Vibrio cholerae. The disease is transmitted by consumption of contaminated water. The low socio-economic status, utilisation of common water sources for bathing, cooking, drinking and washing utensils predispose to infection (51). The consumption of copepod carrier present in such water sources cause infection. The fluctuation of the climatic conditions has a direct relation on the survival of the same. Climate is one of the contributing factors for cholera infection in India (52). In a systematic review conducted in India, it was found that the cholera outbreaks peak (61%) during the monsoon (53). However, the only exception was the state of Tamil Nadu which peaked during winter. It was also identified that the common modes of transmission were leaking pipeline, inadequate sanitation, and food source in social gatherings. Among the Indian states-Gujarat, Karnataka, Maharashtra, Punjab, and West Bengal had a recurrence of cholera every year from 2011-2019. Around 18% of cases were reported from Karnataka, 17% from West Bengal, 10% from Maharashtra, 9% from Gujarat, 9% from Punjab, 6% from Assam, 5% from Madhya Pradesh, 4% from Tamil Nadu, and 3% from Odisha (53).

Shigellosis: Shigellosis is caused by the gram-negative bacilli Shigella spp. The organism was named Shigella spp., in the memory of Shiga K who identified the organism from cases of bacillary dysentery in Japan (54). These isolates were named as Shigella dysenteriae. Soon similar species were identified and placed under this genus were named after Flexner, Sonne, and Boyd (55). Among the Shigella species, Shigella boydii is restricted to India and neighboring countries (56). However, other species are also reported from the country. The Shigella species have a cyclical pattern of occurrence over the years as reported from the National Institute of Cholera and Enteric Diseases (NICED) Kolkata (57). The most prevalent was S.flexneri (60%) followed by S.sonnei, (23.8%) S.dysenteriae (9.8%), and S.boydii (5.7%) (57). Several outbreaks have been reported from West Bengal, Tripura, Kerala, Maharashtra, Chandigarh, Tamil Nadu, and Andaman and Nicobar island (57). Outbreaks of Shigella are attributed to poor hygiene, contaminated water, close personal contact with infected person, and climate. The average increase in rainfall and temperatures is shown to influence the transmission of the infection (58).

Leptospirosis: Leptospirosis is a febrile illness caused by aerobic, motile delicate bacilli of the genus Leptospira. They are transmitted by direct contact of water contaminated by urine of rodents (59). The survival of the organism requires optimum temperature of 30°C. The incidence of Leptospirosis increases >100 cases per 100000 population in a humid temperature (60). The incidence of Leptospirosis has a direct link with the monsoon. The number of cases in India peak following heavy rainfall. In a systematic review the overall 23% (23/127) of global outbreaks were due to increased rainfall and flood (61). Similar peaks were reported from many states in India following the monsoon (62). In a study conducted in Kerala, the peak cases were in August, September, and October which was preceded heavy rainfall of 7-10 days ahead (62).

Schistosomiasis: Schistosomiasis is a parasitic infestation caused by Schistosoma species which are mostly indigenous to the African continent (63). The common species which are present in Asian continent are S.japonicum, S.mekongi, and S.malayensis. The organism is transmitted by the cercaria present in the snails. The first case of Indian Schistosomiasis was identified in 1903 followed by several sporadic cases. Three endemic foci of infection have also been identified in parts of India. It has been reported from Madhya Pradesh, Maharashtra, Kashmir, and Tamil Nadu (64). The presence of snails in aquatic bodies such as rivers, ponds, dams, with associated unhygienic practice predispose to infection. These water bodies and snail population could be influenced by the prevailing rainfall.

Other infections: The extreme events such as precipitation and flooding during the monsoon could cause faecal contamination of water predisposing to diseases such as echinococcosis, taeniasis, and toxoplasmosis (65).

4. Respiratory Infections

Influenza: Influenza is a seasonal infection caused by the virus which can undergo antigenic variation. The virus also shows temporal and geographic variation which determines the control strategies (66). The estimated global mortality ranges from 250,000-500,000 mortality annually (67). It causes influenza like illness (fever, cough, and sore throat) or Severe Acute Respiratory Illness (SARI) with breathlessness or pneumonia (68). In study conducted in Tamil Nadu various types of influenza virus including 86% of A/(H1N1) pdm09, 13.8% of A/H3N2, and 0.12% seasonal A/H1N1 were isolated over a seven-year period (69). It was also observed that the increase in cases were with the onset of monsoon with a peak during the highest rainy days. This was correlating with most studies from other parts of South-East Asia including Singapore, Thailand, Vietnam, and Myanmar (70). The virus survives in lower temperature and during the premonsoon and postmonsoon and has effective transmission due to increase in the half-life (71). Low humidity and temperatures are the factors favouring the transmission. In addition, the decreased activity of proteases aids the stability and survival of the virus in the epithelial cells.

Conclusion

Monsoon is a periodic seasonal climatic change which brings ample rainfall to the Indian subcontinent. The rainfall associated change in temperature and floods favours the survival of infectious diseases and their transmitting vectors. India being a developing country has more vulnerability to such infections. A better strengthening of the infrastructure and health policies is the need of the hour to curb the infections in the Indian setting. Implementation of vector control measures, effective disaster management, improvement of socio-economic status is critical. In addition, relation of monsoon and infectious diseases remains yet unfamiliar. Further studies on the association of infectious agents would aid decision makers in better management during crisis. Though there is limited data on climate change associated infectious disease pattern. The aim of this review is to provide an overview of the infectious disease pattern during the monsoon in the Indian setting. However, meta-analysis or systematic review on the same topic could provide better insights.

DOI and Others

DOI: 10.7860/JCDR/2023/61624.17718

Date of Submission: Nov 18, 2022
Date of Peer Review: Dec 06, 2022
Date of Acceptance: Dec 24, 2022
Date of Publishing: Apr 01, 2023

AUTHOR DECLARATION:
• Financial or Other Competing Interests: None
• Was Ethics Committee Approval obtained for this study? NA
• Was informed consent obtained from the subjects involved in the study? NA
• For any images presented appropriate consent has been obtained from the subjects. NA

PLAGIARISM CHECKING METHODS:
• Plagiarism X-checker: Nov 19, 2022
• Manual Googling: Dec 02, 2022
• iThenticate Software: Dec 20, 2022 (10%)

ETYMOLOGY: Author Origin