A1- What factors do yellow fever and malaria have in common?
Yellow fever and malaria are both transmitted to humans by infected mosquitoes as viral or
parasitic infections. The symptoms of both are similar as including headaches, weakness, chills,
fever, muscle cramps, nausea, and back pain which generally begin to appear in a week and can
lead to serious complications (WHO, 2009). Both are common in developing nations as some
regions of Africa, and South America, typically tropical areas with high rainfall giving breeding
places to mosquitoes.
A2- What factors are different in comparing the two diseases?
There are critical differences between yellow fever and malaria. Yellow fever is an acute viral
haemorrhagic disease belonging to Flaviviridae family (Easmon, 2005). Malaria is caused by a
parasite from the species of plasmodium. The incubation period of malaria is 7 to 30 days as
compared to yellow fever which has incubation period ranging from 3 to 6 days (WHO, 2009).
There is no vaccination for malaria as compared to yellow fever, which has an effective
vaccination effective for a long period (Public Health Agency of Canada, 2008). Yellow fever
infection can cause severe illness and death. Up to 50% of severely affected persons without
treatment will die from yellow fever. As in severe cases, yellow fever can lead to bleeding,
yellowing of the skin and eyes, organ failure and even death. Malaria can cause severe anemia,
kidney failure, acute respiratory infection, coma and even death (Bupa, 2008). Finally, an
individual infected with malaria does not get immune to malaria and can contact the infection
again, as regarding to yellow fever which has not been found to infect an individual previously
infected (New York Department of Health, 2006).
B- Why are yellow fever and malaria not threats at present in North America?
The eradication campaigns in 1940s and 1950s decreased the threat of malaria and yellow fever
in North America (Lentnek, 2007). The widespread outbreaks of malaria motivated the U.S
Public Health Service to fight against malaria using DDT as pesticide in malarial control
worldwide (Centers For Disease Control And Prevention, 2004). The infected mosquitoes were
removed and breeding places of mosquitoes were destroyed which led to decline in the cases of
malaria and yellow fever. Moreover, in temperate zones which are characterized by strong
seasonality and cold winter, malaria and yellow fever are effectively controlled (Sachs, 2002).
C- Why is malaria such a significant hazard in Africa?
Poverty-stricken communities such as Africa do not have the resources to protect their residents
from malaria (EHS, 2005). In the United States, a long-lasting, insecticide-treated bed net would
cost about $10; a full course of malaria medications, only $5. But many people in Africa are
living on less than $2 a day and can't afford to buy these life-saving items (Global Ministries,
2009). Technical obstacles in malaria control in Africa such as insecticide resistance, vector
behaviour, drug resistance in malarial parasites, financial problems in acknowledging the poor community is a really important determinant in malarial spread (Sharma, 2003). The civil wars in
Africa cause migration of individuals to different areas as the ones heavily infected by malaria.
The environmental degradation leads to malaria transmission more frequently. The high birth
rates in Africa and no access to primary health care increases the risk of the population to be
infected with malaria (Jacobs, 2009).
D- Why does the number of West Nile virus cases in people increase in warmer weather?
Mosquitoes are not evenly distributed. The global pattern of mosquito’s related infections is
centered in the tropics. The temperate zones with strong seasonality and cold winter do not
provide good breeding places for mosquitoes. The standing and stagnant water of about four
days gives opportunities to mosquitoes to build nests and habitats. They usually do not breed
near moving water such as currents, and do not necessarily require naturally found standing
waters such as ponds. Rather, they are able to build nests out of birdbaths which have older
water, pools, marshes, tires which collect water and even garbage cans which collect water
(Sachs, 2002). As related to temperature, mosquitoes are usually active during a time period
from June to September when humidity is high and temperature is warm (Apperson and
Waldvogel, 2004). The high rainfall in summer increases the mosquito’s habitats and
reproductive success. Since, the greater number of mosquitoes leads to the high probability of the
population to get infected with West Nile Virus and the greater chance of the transmission of
passing it on to the other individuals. All these reasons make individuals more susceptible to
West Nile infections in warmer weather.
2A- Why are animals used in laboratory experiments in toxicology?
Toxicology is the study of harmful effects to living organisms from substances which are foreign
to them. The toxins may be naturally occurring in the environment or synthetic chemicals.
Following the birth of the synthetic chemical industry in the late 1800s, the field of toxicology
grew in response to the need to understand how tens of thousands of new substances might affect
the health of workers and consumers involved in their production and use. The use of living
animals to study the potential adverse effects of new drugs, food additives, pesticides, and other
substances began in earnest during the 1920s.Today, most developed countries have enacted
laws and regulations to control the marketing of drugs, vaccines, food additives, pesticides,
industrial chemicals, and other substances of potential toxicological concern. Such regulations
often prescribe a specific regime of toxicity testing to generate information that will enable
government regulators to determine whether the benefits of a particular substance outweigh its
risks to human health and/or the environment. Therefore, animals are used in regulatory risk
assessment as hazard identification includes the determination of a substance's intrinsic toxicity
(e.g., eye irritation, birth defects, or cancer) through the use of toxicity tests. The determination
of the extent of human and/or environmental exposure to a substance, including the identification
of specific populations exposed their composition and size, and the types, magnitudes,
frequencies, and durations of exposure. A composite analysis of the hazard and exposure
2 assessment results to arrive at a "real world" estimate of health and/or ecological risk (General
Toxicology, 2010). Animals such as rats, rabbits are used in laboratory testing as they have
similarities to the human genome in acting against foreign substances. Animals have small
gestation period, they mature quickly, and their offspring can be obtained in a small period of
time, which enables researchers to study the effects of a particular substance on an individual as
well as on the offspring minimizing the dangers related to the usage of the particular substance.
2B- Explain the dose-response curve.
Dose-response curves can be used to plot the results of many kinds of experiments. The X-axis
plots concentration of a drug or hormone. The Y-axis plots response, which could be almost
anything. For example, the response might be enzyme activity, accumulation of an intracellular
second messenger, membrane potential, secretion of a hormone, heart rate or contraction of a
muscle. A dose-response defines the relationship based on a number of important assumptions.
The first assumption is the response increases as the dosage is increased. The second assumption
is that there is a threshold potential. A threshold potential is a dosage concentration below which
there is no response. The lowest experimental dose which does not have a response of
measureable effect is known as the No Observable Effect Level (NOEL). Another factor which
is usually assumed is that once a maximum response is reached any further increases in the dose
will not result in any increased effect (Extoxnet, 1993). Using the dose-response curve, several
factors can be determined, including the EC50. The NOEL point can be recorded, as well as the
maximum effect. EC50 is the drug concentration which invokes a response halfway between the
maximum effect, and the baseline (NOEL) point. Also, the potency of a drug can also be
measured. The potency of a drug or product is drug activity that is expressed in terms of the
amount required to produce an effect of given intensity (University of Ottawa, 2009).The
potency helps determine the strength of the drug, which alters