Background : Ten percent of the total population of the State of Maharashtra belongs to tribal population groups. These groups remain isolated, living in remote forest and hilly areas far from civilization. Nandurbar district has been a newly carved tribal district (July 1998). Objective : To find out the prevalence of various type of malaria and to see the correlation between rainfall and incidence of malaria cases. Materials and Methods : It was a retrospective, cross sectional study carried out during 1999 to 2004. The reports from the years, 1999 to 2004, were taken from district health office and district malaria office, respectively. Results : There were total 5228 cases of malaria; out of these, 3237 were Plasmodium vivax (PV) cases, and 2001 were Plasmodium falciparum (PF) malarial cases, during the years, 1999 to 2004. In the years, 1999 to 2002, percentage of PV malaria was more than PF malaria. Majority of PV malaria cases was observed in the year 1999. In the year 2004, the PV malaria started showing an upward trend in Nandurbar district, Maximum numbers of cases were reported in rainy season as compared to winter and summer seasons. It was observed that the PF cases were increased during the months of July to October, every year. It was also observed that as rain fall increases, the number of malaria cases also increases. Conclusion : There is an upward trend of malarial cases in the tribal block. Incidence of malarial cases closely correlates with the rainfall.
Keywords: Malaria, rainfall, tribal region
Ten percent of the total population of the State of Maharashtra belongs to tribal population groups. These groups remain isolated, living in remote forest and hilly areas far from civilization. Majority of them have poor health status, peculiar health needs, and a wide prevalence of red blood cell genetic disorders that complicate their health problems.
Malaria is an internationally devastating disease, producing nearly 600 million new infections and 3 million deaths each year. Malaria, a disease of antiquity, has proved to be a formidable deterrent to the cultural and socio-economic progress of man in the tropical, sub-tropical, and monsoon prone zones of the world.
Recent estimates indicate that due to malaria, 300-500 million clinical cases and 1.5-2.7 million deaths occur worldwide, annually, 90% of which occur in tropical Africa. It is estimated that 1.2 billion people out of the 1.4 billion people of SE region lives in malaria prone areas. In 1995, malaria cases in this region were estimated to be 21.9 million, with almost 32,000 deaths. India accounts around 85% of the total reported cases in the region, in the same year. During 1996 also, India contributed 83% of total malaria cases in SE region. Thus, around 80% of reported cases in the region are being contributed by India. 
Malaria is a complex disease, and various factors influenced by human activities and natural calamities like excessive rainfall, flood, drought, and other disasters have great bearing on genetic makeup of mosquito eading to increased potential for malaria transmission. Like any other disease, natural transmission of malaria depends on the presence of, and relationship between the three basic epidemiological factors: the agent, the host, and the environment.
Study area – Nandurbar district profile
Nandurbar district has been a newly carved district (July 1998). It covers an area of 5035 sq. Km with a density of population of 260/sq. Km. It has 6 blocks, 938 villages, and 1534 padas. Sixty six percent of the population is tribal. Much of the part is spread in Satpuda ranges and Narmada Valley. This district lacks facilities of transport and communication. Primary health center and sub center covers an area of 35.50 Km and 15-20 Km, respectively. It is characterized by heavy rain fall. Poverty and low literacy are the major issues in this district.
Study duration: 1999 to 2004
Study type : retrospective, cross sectional study
The reports from the years, 1999 to 2004, were taken from district health office and district malaria office, respectively.
There were total 5228 cases of malaria; out of these, 3237 were Plasmodium vivax (PV) cases, and 2001 were Plasmodium falciparum (PF) malarial cases, during the years, 1999 to 2004. In the years, 1999 to 2002, percentage of PV malaria was more than PF malaria. Majority of PV malaria cases was observed in the year 1999. In the year 2004, the number of PV malaria cases started showing an upward trend in Nandurbar district. It was observed that malaria cases were increased in the year 1999, while they were decreased during the years, 2000-2003, and again rises in the year, 2004, in all the blocks of Nandurbar district [Figure 1].
Earlier to 1999-2000, there was a high prevalence of malarial cases in all the blocks. Prevalence has shown a dip in the year 2002, and again an upward trend in 2004 [Figure 2].
Seasonal trend was observed during 1999 to 2004, maximum numbers of cases were reported in rainy season as compared to winter and summer seasons. It was observed that the PF cases were increased during the months of July to October, every year [Figure 3] and [Figure 4].
Metrological aspects of malaria
It was also observed that as rain fall increases, the number of malaria cases also increases [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9] and [Figure 10].
In order to implement an effective malaria control program, accurate information on the incidence and prevalence of malaria is required. In this study, the first malaria prevalence survey was conducted to provide the baseline parasitological information for population living in the malaria endemic district. This cross-sectional survey provides point prevalence data on malaria in this malaria endemic district. These data will also be a massive help for the global initiatives of malaria mapping. 
We have found a much higher prevalence of malaria than the expected, by investigating the National Passive Surveillance information.  Malaria is not equally distributed in all malaria endemic districts of India. Prevalence of malaria is significantly higher in the hill tract districts. The reason might be that districts are hilly and covered with forests and lakes; thereby providing an excellent habitat for malaria vectors.  Resources should be differentially targeted to this area, because of its larger malaria burden.
The combined use of GIS (geographic information system) and remote sensing provides a significant tool to control malaria.  We hope GIS and high resolution satellite images can be used to detect malaria hot spots and vectors habitat sites.
From this study, it is also clear that P. vivax is the dominant species in the malaria endemic district. Rainfall has been closely related with the prevalence of malaria similar to study carried out by Rozendaal.  Seasonal variation was also observed. 
Longitudinal studies are needed to assess the variation of asymptomatic parasite carriage over time and its exact contribution to transmission. Population-based prevalence studies on a regular basis are required to understand the burden of the disease. More studies should be conducted in the future to map the changing malaria epidemiology in tribal district as control activities are scaled up.
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]