Climatological influence in the epidemiology of leptospirosis in humans in SVG

Dr Eric Alanzo Audain Tue, Sept 4, 2012

Part 2 – Behavioural pattern of Leptospirosis in HumanS in SVG

The number of reported confirmed clinical cases of leptospirosis in humans in St Vincent and the Grenadines has shown a similar behavioural pattern with regard to the occurrence of the disease on a yearly basis, over the period 2001-2010.{{more}}

As mentioned in Part 1 of our publication, leptospirosis is a seasonal, occupational and environmental disease. This is because the Leptospira (bacteria) are constantly being eliminated into the environment through the urine of infected rats. These rats are chronically infected by the disease and do not get sick. However, they do infect one another by contaminating their environs and so the bacteria remains within the population of rats for life and is eliminated every time they urinate.

When a rat becomes infected with Leptospira, within a particular period, the bacteria move from their blood stream and enter the kidneys, where they seek permanent residence. The rat eventually develops a chronic form of kidney infection which results in the bacteria being eliminated into the environment in the urine of infected rats. The bacteria are also eliminated into the environment by means of the urine of infected dogs, cats, cattle, horses and pigs etc. The high Ph (acidity) of human urine kills the bacteria and, as such, human to human transmission through human urine is very rare.

The occurrence of the disease depends greatly on the level of bacterial contamination that transpires in our environment, which depends on the population of rats and the amount of bacteria eliminated in their urine. Other factors include: precipitation (rainfall), temperature, humidity, soil type and Ph, just to mention some elements that significantly influence the manifestation of the disease.

Over the period (2001-2010), 83 per cent of the confirmed clinical cases of leptospirosis in humans in SVG occurred during the rainy season when 80% (17,493 mm) of the rainfall was recorded. The number of confirmed clinical cases of the disease varies during the months of the rainy season. Our results show that from the 83% of all confirmed clinical cases of the disease, 42% of these cases occurred during the month of October. This is as a result of the accumulation (mm) of rain fall over a period of time. Our results show that once there is an accumulation of 550 mm of rainfall in SVG, the number of confirmed clinical cases of leptospirosis in humans tends to increase. Of all the reported confirmed clinical cases of leptospirosis in humans during the dry season, the highest number of cases were recorded in January, March and April.

Temperature is a known factor that may influence the manifestation of leptospirosis in humans. Our result shows that in SVG (2001-2010), the average temperature varies (25.8 – 28.0) throughout the months and years. Such a temperature is ideal for the future survival of the bacteria while in the environment. The highest temperature readings were recorded during the months of August and October (27.7 and 28.0) respectively. The atmospheric humidity affects the soil and so creates a condition that is favourable for the survival of the bacteria. The high level of precipitation (rainfall) creates conditions that are conducive to the bacteria. It must be clearly established that the bacteria do not reproduce in the environment, but merely exist in a vital state and await the opportune time to penetrate a susceptible animal or it may accidentally contaminate fruits, vegetables, root crops and any other food, including drinking water and meat.

To be continued next week