Disease detectives
1. There are many diseases we know about and understand the causes of. However, sometimes there are outbreaks of a disease that are unexpected and nobody understands why so many people are getting sick.
2. Today, I’m going to discuss two case studies, one in Senegal, in West Africa, and the other in Guam, an island in the Pacific Ocean. In both places, there were epidemics affecting many people. Researchers had to investigate the causes of these epidemics.
3. The first situation, in Senegal, concerns a disease called schistosomiasis. Schistosomiasis is caused by a parasite released into rivers by freshwater snails. When anyone comes into contact with the river, the parasite is transmitted to their skin, causing fevers, coughs, stomach pains, and general sickness. 解释血吸虫病发生的原理
(Concern= is about. Sch. Is caused by a parasite…)
4. Although schistosomiasis is one of the most common diseases from a parasite in the world, no one in this part of Senegal had had it before 1986 – the year the Diama Dam was built on the Senegal River. Soon after the dam was built, people started to become ill. In fact, by 1988, 90% of the population had come down with the disease. Finding a solution to this health crisis became critical. After a lot of research, scientists traced the problem back to the dam. This is what they found. 解释这一地区爆发血吸虫病的年份及相关事件可能性
Had =have/has done = had the disease
(Although sch. …, no one in Senegal had had it before 1986!!! What happened in 1986? The building of the D Dam = The construction of a new dam = B)
*2 Soon after the dam was built, ppl stated to become ill.
*3 After …, scientists traced the problem back to the dam. (trace back to = find the origin of)
5. Before the dam was built, there were a lot of prawns in the Senegal River. The prawns ate the freshwater snails that lived in the river, and there was no disease. However, the construction of the dam caused the water in the river to flow differently. This, in turn, changed the prawns’ natural habitat, and eventually led to their extinction. With no natural predators left in the river, the snail population increased rapidly. More snails led to more parasites in the river water, and suddenly many people started to become very ill.解释水坝对该地的影响
• Why did the prawns go extinct? How did this affect the spread of schistosomiasis?
• Prawns went extinct because the construction of the dam changed their habitat. Without prawns, the river snails no longer had any natural predators, so the number of snails increased. Because they carried parasites, many people contracted schistosomiasis.
(contract v. 1. to become less or smaller 收缩 eg: Glass contracts as it cools.
2. to get an illness 感染，得（病） eg: to contract AIDS/ a virus/ a disease)
The causal chain about the outbreak of schistosomiasis
Construction of the D Dam ——>extinction of the prawns ——>multiplication of the snails ——>increase of the parasites in the river ——> outbreak of schistosomiasis
6. A group of researchers called “Project Crevette” decided that the best way to eliminate the disease was to restore the environmental conditions of the river so the prawns would be able to live there again. If the prawns returned to the river, they would eat the snails. This would mean fewer parasites in the river and ultimately less disease. This approach to solving a health problem is significant because it focuses on the main cause of the disease rather than simply giving people medicine to treat the disease. 设置解决方案的构想
(Q2. What was the objective of the Project Crevette？
（to restore the environmental conditions of the river so the prawns would be able to live there again = reintroduce prawns to the river = C）
eliminate v. to remove or get rid of sth/sb. 排除，清除，消除 to eliminate a disease/poverty
7. Now, let’s look at a case study in Guam – a small island in the Pacific Ocean. In the late 1940s, the local people – known as the Chamorro – contracted a neurological disease called lytico-bodig. As the disease only seemed to affect the Chamorro, scientists argued that something in their diet must be the cause. 第二种疾病爆发的区域独特性，引起专家推测
（Q3. What was the main cause of the lytico-bodig outbreak in Guam？
——something in their diet must be the cause. When you make deductions about the present: 1. use must/have to +root form (for sure) 2. Use couldn’t/can’t + root form (not sure)
8. Every day, the Chamorro made bread using the seeds of the cycad plant. These seeds were known to contain a toxin, so researchers initially thought that the flour must be the cause of the epidemic. However, the seeds were washed several times before they were used and this removed most of the toxins, meaning that the flour couldn’t have caused the disease. 推测一
Possibility 1: seeds, toxin = be poisonous,
were washed = no toxins
9. At this point, the researchers discovered two interesting facts – more men had the disease than women, and men ate more meat than women. The most commonly eaten meat in the area was the flying fox, and the flying fox regularly ate the seeds of the cycad plant. This meant that there was a high concentration of toxins in the meat of the flying fox, and this fact led researchers to suspect that the meat may have been the cause of the epidemic. Later, they learned that when the flying fox population declined (due to overhunting), the incidence of lytico-bodig also started to decrease, and this confirmed that flying fox meat was the cause of the epidemic. 观察，推测，确认，第二种可能性
Interesting facts!!! = important facts! More men, more meat = more disease
Flying fox, ate seeds = toxins in the meat——>disease
*2 overhunting —> flying fox declined —> disease decrease —>
flying fox meat was the cause
• How was the flying fox related to lytico-bodig?
L.B. was caused by toxins in the seeds of cycad in Guam. The flying foxes ate the seeds, so there was a high concentration of toxins in the meat of the flying foxes. When people ate the meat, they contracted L.B.
10. So these are just two examples of the various factors that need to be taken into account when investigating an unusual incidence of a disease. Personally, I think they are quite interesting case studies because they demonstrate that while researching diseases can be challenging, it’s also incredibly rewarding. 总结
(Q4. What did the two case studies demonstrate?)
=to show sth. Clearly by giving proof or evidence 证明，to show 表明
