Student Name Public Health Biology

Midterm: 2012

1. Disease pattern changes, or the “emergence of diseases” is generally due to changes in what four elements? For each element, name a specific disease and discuss the change associated with its outbreak, change or emergence as a public health phenomenon.

Answer:
There are four elements including (1)human population (2)pathogen (3)reservoir and (4)vectors. The dynamics of diseases depends on the overlap of niches of these elements.
1. Human population :
Disease patterns and processes reflect interactions of individuals within populations. Many diseases such as lung cancer or pulmonary diseases emerge as increasing urbanization results in higher air pollution.
2.Pathogen :
Such as chloroquine resistance in malaria Parasites, the microorganism presents drug-resistant due to frequent mutation in response to antibiotic/drug treatment.
3.Reservoir :
Rabies outbreaks are related to concurrent increased human activity that contact with animals.
Rabies is a zoonotic disease that is caused by a virus. The disease infects domestic and wild animals, and is spread to people through close contact with infected saliva via bites or scratches.
4.Vectors :
Japanese encephalitis is a disease transmitted via mosquitoes from Domestic pigs and wild birds. The outbreak occurred when the vector mosquitoes proliferated in rustic countries in summer. The widespread use of vaccine and cleaning living environment can control of the disease.

Public Health Biology

2. Compare and contrast the Salk killed polio vaccine (IPV) and the Sabin live, attenuated polio vaccine (OPV) in terms of effectiveness, duration of immunity, safety, and ease of distribution. State under what conditions the use of one is preferable over the other.

Answer:
Polio can be spread through contact with infected feces or through infected droplets traveling through the air, in food, or in water. There are two types of vaccines which are killed polio vaccine and live-attenuated vaccine.
1. These two vaccines have very different immunological and public health properties.
(1) Sabin: Oral polio vaccine (OPV) is a live-attenuated vaccine. It can be presented by B cell with MHC class II and by dendritic cell with MHC class I, so that induces both humoral immunity and cell-mediated immunity (2) Salk: inactivated poliovirus vaccine (IPV) is a killed polio vaccine. The antigens of the killed vaccine is processed and presented on MHC class II and provokes helper T cell (TH or CD4+) response to induce the humoral immunity. OPV IPV effectiveness 1.Induce both humoral immunity and CMI
2.The prevention of reinfection of the digestive tract. 1.Induce humoral immunity
2.Less gastrointestinal immunity duration of immunity Long-lasting immunity Shorter safety The possibility to revert to a form and maybe cause disease in these immunocompromised patients More safe for those with compromised (weakened) immune systems. ease of distribution Easy difficult

2. What conditions the use of one is preferable over the other. (1)Sabin OPV is more suitable in epidemic area. It can be distributed easily and block the oral-fecal transmitted route with increasing the gastrointestinal immunity. (2)Salk IPV is more suitable in area where only sporadic cases are discovered. The reason is IPV is more safe than OPV which maybe cause the disease. Besides, the live virus (Sabin OPV)also has stringent requirements for transport and storage, which are a problem in some hot or remote areas.

Public Health Biology

3. Name the three mechanisms of drug resistance by microorganisms. For each mechanism, provide an example by way of the name of a drug and its originally intended microbiologic target.

Answer
Three mechanism of drug resisstance are mentioned:
1. Change in the target protein to reduce drug binding:
Pyrimethamine can inhibits DHFR, which occurs in most organisms. Through the mutation to get small differences in the amino acid sequences of plasmodium enzymes give them different shapes (DHFR). By this way, it can reduce drug (pyrimethamine) binding. And it is necessary to increase the concentration of drug in vivo to achieve the antiseptic effect, sometimes the drug levels are unachieveable.
2. Reduction in the intracellular drug concentration by pathogen:
The cefoxitin-resistant E coli isolates can change the outer membrane channel due to mutation with loss of the major porin channel (OmpF) in the outer membrane and inhibit cephamycins to enter the cell.
Mutation of PfCRT gene in plasmodium falciparum result in expression of chemical pumps that cause resistance to chloroquine.
3. Drug destruction by the pathogen:
Some organisms produce enzymes such as beta- lactamase that destroy the antibacterial agent before it can have an effect. These are often carried on mobile genes such as plasmids which transmit between bacteria.
Methicillin-resistant Staphylococcus aureus (MRSA) has developed beta- lactamase to destroy beta-lactam antibiotics, which include the penicillins and the cephalosporins.

Public Health Biology 4. Genome wide microarray assays have identified Anopheles mosquito genes whose expression is affected by Plasmodium species infection. Name four genes and classify each as contributing to either innate or adaptive immunity.

Answer:
1. Pattern recognition receptors are respond to pathogen-associated molecular patterns and endogenous stress signals termed danger-associated molecular patterns. So, it is belonged to the innate immunity
2. Proteases (effectors and signalling) can breakdown peptide bonds of proteins. Such as human oral proteases can hydrolyze the extra-cellular proteins. It is not specialized. So, it is belonged to the innate immunity.
3. Melanization enzyme process varies in different insect species and affect human immunity system ability. So, it is belonged to the adaptive immunity.
4. Antimicrobial protein and peptides to generate protein could disrupt microbial structures and kill bacteria. It is not evoked by special proteins. So, it is belonged to the innate immunity

Public Health Biology

5. Explain the difference between net reproductive ratio and effective reproductive ratio both conceptually and in the context of a specific disease infectivity. In terms of Re and Ro, what is the goal of a vaccination campaign intended to eradicate an infectious disease, and why?

Answer:
1. Net reproductive ration (Ro)
The basic reproductive rate for a finite period of time of the pathogen first in the host population when resources (hosts) are not limiting. Number of secondary case caused by a primary case is not limited and could be calculated. Every individual in this population is susceptible to the pathogen.

Ro = Number of secondary cases = B * N * D
−B = Transmission parameter
−N = Population size of susceptibles
−D = Duration of infectiousness

(1)If Ro> 1: then each primary case produces more than 1 secondary case. It means disease epidemic
(2)If Ro< 1: then each primary case dose not produce enough cases to replace itself. It means disease should die out.
(3)If Ro= 1: then each primary case replaces itself. It means disease will continue to persist endemically.

2. Effective reproductive ratio ( Re)
The average number of secondary cases per primary case after pathogen is established
The susceptible population size should be smaller than original population size due to a pathogen that is established in a human population, previously infected individuals either die or are immune.

Re is the product of transmission parameter (B) and size of susceptible population (X) and duration of infectiousness (D).

Temporal pattern determined by rate of introduction of susceptibles into population (X)
(1)If susceptibles come into the population rapidly, then disease tends to be endemic
(2)If susceptibles come in slowly, then disease tends to be epidemic
(3)If susceptibles come in too slowly, then disease dies out

3. Ro and Re are both key measures of how a pathogen acts in a host population. The dynamics of infection in a host population depends on the rate of spread when a new pathogen appear (Ro) and on the rate of transmission (Re) when a pathogen is established.

Control of epidemics and eradication of disease through use of vaccines does not require that all members of the community be vaccinated.
There is an indirect protection to unvaccinated individuals by not serving as a bridge between the infectious and unprotected individuals. This is so called the herd immunity

If some fraction of population is protected (p), then the remainder (1–p) is not directly protected. The goal of a vaccination campaign intended to eradicate an infectious disease is making sure the value of (1-p)Ro is now less than 1 so that the pathogen will not be able to persist in the unvaccinated population.