Cholera

The patterns of bacterial diseases are determined by the method of transmission which consists of the pathogen, vector, and host. Important factors such as temperature, humidity, precipitation, water, soil, and vectors play different roles in disease transmission and virulence. Vectors, such as copepods, boost in population size after increased in rainfall and warm sea surface temperatures. These increases, which have been attributed to El Nino, are correlated with Cholera outbreaks all over the world.

Cholera outbreaks provide a paradigm in climate change and infectious disease. The disease is caused by bacteria called V. cholerae and copepods are used as their primary vectors, thus their abundance is dependent on copepod population size. Copepod blooms often thrive in nutrient rich warm waters and it has been predicted that the warmer waters due to global warming will further encourage their growth as seen in cases of outbreak closely following El Nino events. Since copepods live in marine and freshwater environments, water is the key factor in the spread of this disease. The disease causes diarrhea and vomiting if ingested, then eventually death just after a few hours of exposure. A single copepod can carry up to 10^4 cells of V. cholerae and an infectious dose has been reported to be 10^3 cells in humans. Several copepods can easily be ingested in a glass of water if there is no treatment of the water supply. This makes coastal communities that are low in levels of poverty, health education, and sanitation susceptible to high numbers of infection after exposure to El Nino warmed waters. Copepods and V. cholerae can be seen in ocean waters over wide geographical ranges. The viability and hardiness of cholera allows the disease to be transported even in nutrient poor seawater and can travel for thousands of kilometers over a period of several months. Even northern countries such as the United States and Canada are predicted to be affected by cholera in due course.

Copepod carrying cholera

Coastal cities stricken with poverty, such as those found in Peru for example, are now at an even higher risk due to the increased frequency of El Nino events. Synthesis of satellite remote sensing and meteorological data sets show plankton blooms as a result of warmer waters. Cholera distribution and El Nino event frequency have been increasing for the last few decades. This is direct evidence showing that cholera outbreaks follow rises in ocean surface temperatures. The most recent devastating outbreak of cholera was in Peru in 1991, where nearly 1.5% of the entire population suffered from the disease. The outbreak was able to spread quickly to other countries such as Ecuador, Columbia and even as far as Mexico. The far spread distribution of cholera is attributed to changes in water currents brought on by the El Nino event. There is high statistical evidence showing that the increased copepod distribution is a direct result of El Nino events and that the two events were not coincidental.