BACTERIAL INFECTIOUS DISEASES
- "Black Death"
- Bubonic plague
- Septicemic plague
- Pneumonic plague
- Yersenia pestis bacteria
- Global Warming
- Cycles of Poverty
- Invasive Species
Bubonic plague is an infection of the lymphatic system, usually resulting from the bite of an infected flea, Xenopsylla cheopis (the rat flea). The fleas are often found on rodents such as rats and mice, and seek out other prey when their rodent hosts die. The bacteria form aggregates in the gut of infected fleas and this results in the flea regurgitating ingested blood, which is now infected, into the bite site of a rodent or human host. Once established, bacteria rapidly spread to the lymph nodes and multiply. Y. pestis bacilli can resist phagocytosis and even reproduce inside phagocytes and kill them. As the disease progresses, the lymph nodes can haemorrhage and become swollen and necrotic. Bubonic plague can progress to lethal septicemic plague in some cases. The plague is also known to spread to the lungs and become the disease known as the pneumonic plague. This form of the disease is highly communicable as the bacteria can be transmitted in droplets emitted when coughing or sneezing, as well as physical contact with victims of the plague or flea-bearing rodents that carry the plague.
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- Borrelia burgdorferi sensu stricto (US) bacteria
- Borrelia afzelii (Europe) bacteria
- Borrelia garinii (Europe) bacteria
- Habitat Conversion
Lyme disease is the most common tick-borne disease in North America and Europe, and one of the fastest-growing infectious diseases in the United States. Of cases reported to the United States CDC, the ratio of Lyme disease infection is 7.9 cases for every 100,000 persons. In the ten states where Lyme disease is most common, the average was 31.6 cases for every 100,000 persons for the year 2005.
Although Lyme disease has been reported in 49 of 50 states in the U.S, about 99% of all reported cases are confined to just five geographic areas (New England, Mid-Atlantic, East-North Central, South Atlantic, and West North-Central). New 2008 CDC Lyme case definition guidelines are used to determine confirmed CDC surveillance cases. Effective January 2008, the CDC gives equal weight to laboratory evidence from 1) a positive culture for B. burgdorferi; 2) two-tier testing (ELISA screening and Western blot confirming); or 3) single-tier IgG (old infection) Western blot. Previously, the CDC only included laboratory evidence based on (1) and (2) in their surveillance case definition. The case definition now includes the use of Western blot without prior ELISA screen.
The number of reported cases of the disease has been increasing, as are endemic regions in North America. For example, B. burgdorferi sensu lato was previously thought to be hindered in its ability to be maintained in an enzootic cycle in California, because it was assumed the large lizard population would dilute the prevalence of B. burgdorferi in local tick populations; this has since been brought into question, as some evidence has suggested lizards can become infected. Except for one study in Europe, much of the data implicating lizards is based on DNA detection of the spirochete and has not demonstrated lizards are able to infect ticks feeding upon them. As some experiments suggest lizards are refractory to infection with Borrelia, it appears likely their involvement in the enzootic cycle is more complex and species-specific.
While B. burgdorferi is most associated with ticks hosted by white-tailed deer and white-footed mice, Borrelia afzelii is most frequently detected in rodent-feeding vector ticks, and Borrelia garinii and Borrelia valaisiana appear to be associated with birds. Both rodents and birds are competent reservoir hosts for B. burgdorferi sensu stricto. The resistance of a genospecies of Lyme disease spirochetes to the bacteriolytic activities of the alternative complement pathway of various host species may determine its reservoir host association.
It should be noted that several similar but apparently distinct conditions may exist, caused by various species or subspecies of Borrelia in North America. A regionally restricted condition that may be related to Borrelia infection is southern tick-associated rash illness (STARI), also known as Masters' disease. Amblyomma americanum, known commonly as the lone-star tick, is recognized as the primary vector for STARI. In some parts of the geographical distribution of STARI, Lyme disease is quite rare (e.g., Arkansas), so patients in these regions experiencing Lyme-like symptoms-- especially if they follow a bite from a lone-star tick-- should consider STARI as a possibility. It is generally a milder condition than Lyme and typically responds well to antibiotic treatment.
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- Vibrio cholerae bacteria
- Global Warming
- Cycles of Poverty
It is estimated that cholera affects 3-5 million people worldwide, and causes 100,000-130,000 deaths a year as of 2010. This occurs mainly in the developing world. In the early 1980s, death rates are believed to have been greater than 3 million a year. It is difficult to calculate exact numbers of cases, as many go unreported due to concerns that an outbreak may have a negative impact on the tourism of a country. Cholera remains both epidemic and endemic in many areas of the world.
Although much is known about the mechanisms behind the spread of cholera, this has not led to a full understanding of what makes cholera outbreaks happen some places and not others. Lack of treatment of human feces and lack of treatment of drinking water greatly facilitate its spread, but bodies of water can serve as a reservoir, and seafood shipped long distances can spread the disease. Cholera was not known in the Americas for most of the 20th century, but it reappeared towards the end of that century and seems likely to persist.
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