Questions & explanations
1. If a vaccine is given intranasally, what advantage might it have over an intramuscular vaccine for a respiratory virus like influenza?
An intranasal vaccine is sprayed into the nose, where it directly targets the mucous membranes that respiratory viruses first infect. It can produce local IgA antibodies, which are the first line of defense in the nose and throat. This may stop the virus from entering the body altogether, reducing infection and spread. In contrast, an intramuscular flu vaccine mainly raises antibodies in the blood, which protect against severe disease but may not prevent infection as well. Intranasal vaccines can also be easier to give to children who fear needles. However, they may not be suitable for people with weak immune systems.
2. Compare resistance in malaria parasites with resistance in leishmaniasis parasites. How are they similar?
Both malaria and leishmaniasis parasites can become resistant to first-line drugs. For malaria, resistance to chloroquine and artemisinin has emerged. For leishmaniasis, resistance to antimonial drugs like sodium stibogluconate is common in some areas. In both cases, resistance often results from incomplete treatment or using the wrong dose. Also, both parasites can develop resistance through genetic mutations that change drug targets or increase drug efflux. However, malaria resistance spreads faster because the parasite is transmitted by mosquitoes, while leishmaniasis is transmitted by sandflies.
3. Compare bacterial resistance to heavy metals with resistance to antibiotics in terms of mechanisms and spread.
Both types of resistance often involve efflux pumps that expel the toxic substance, or enzymes that modify it. However, heavy metal resistance sometimes uses detoxification (e.g., converting mercury to a less toxic form), which is rare for antibiotics. Resistance genes for both are often carried on plasmids or transposons, enabling easy spread between bacteria. The same mobile elements can carry both heavy metal and antibiotic resistance genes, so exposure to heavy metals can co-select for antibiotic resistance. This is a problem in environments contaminated with metals, like industrial waste.
4. What is parasitology?
Parasitology is the study of parasites and their relationships with hosts. Parasites are organisms that live on or inside another organism, called the host, and get food from or at the expense of the host. There are different types of parasites, such as protozoa (single-celled), helminths (worms), and ectoparasites (like ticks and lice). Host-parasite interactions can harm the host, but sometimes the host is not badly affected. In medicine, parasitology helps us understand and treat diseases like malaria and hookworm. In ecology, parasites can control animal populations and affect food webs.
5. How does Bacillus anthracis cause anthrax, and what are the three forms of the disease?
B. anthracis forms spores that can enter the body through cuts (cutaneous anthrax), inhalation (inhalation anthrax), or ingestion (gastrointestinal anthrax). Once inside, spores germinate into bacteria that produce a capsule and toxins. The capsule prevents immune cells from engulfing them, while the toxins cause tissue damage and shock. Cutaneous anthrax is the mildest, with a black sore. Inhalation anthrax is severe, with fever and breathing problems, often fatal if untreated. Gastrointestinal anthrax causes vomiting and bloody diarrhea. All forms require prompt antibiotics.
6. What is Koch's phenomenon?
Koch's phenomenon is a strong immune reaction that happens when a person or animal already infected with tuberculosis (TB) bacteria is injected with a substance from the bacteria (tuberculin). Robert Koch discovered that guinea pigs with TB developed a severe, fast skin reaction at the injection site, while healthy animals had no reaction. This shows that the immune system remembers the bacteria and overreacts. It is a type of delayed-type hypersensitivity (DTH), meaning the reaction takes 24-48 hours to appear. This phenomenon is the basis for the TB skin test (Mantoux test).
7. What are the challenges in setting up effective AMR surveillance in low-resource settings?
Low-resource settings often lack labs with equipment to test bacteria and trained staff. Collecting and shipping samples can be difficult due to poor infrastructure. Data reporting may be inconsistent, making it hard to get accurate resistance rates. Without surveillance, doctors may use antibiotics without knowing which ones work, worsening resistance. International partnerships and simple, cheap testing methods can help. For example, using filter paper to dry samples for transport or mobile apps for data entry. Overcoming these challenges is critical for global AMR control.
8. What color do Gram-positive bacteria appear after Gram staining?
Gram staining is a method to tell apart bacteria into two groups based on their cell wall. The process uses a purple dye (crystal violet), then iodine, then alcohol, and finally a red counterstain (safranin). Gram-positive bacteria have a thick cell wall that holds the purple dye, so they look purple under a microscope. Gram-negative bacteria have a thin wall and lose the purple after alcohol, so they take up the red counterstain and look pink or red. This helps doctors choose the right antibiotic because Gram-positive and Gram-negative bacteria respond to different drugs.
9. What is the advantage of using an adenovirus vector for a pandemic vaccine?
An adenovirus vector uses a harmless cold virus to carry genetic instructions for the pathogen's protein into human cells. It triggers a strong immune response with just one or two doses. These vaccines can be stored at normal fridge temperatures, making them easier to distribute than mRNA vaccines that need freezing. They have been used for Ebola and COVID-19 (e.g., AstraZeneca, Johnson & Johnson). Manufacturing can be scaled up using existing cell culture facilities. However, some people have pre-existing immunity to the adenovirus, which may weaken the vaccine's effect.
10. Why is it important to update breakpoints regularly? Give an example of a situation where old breakpoints could lead to wrong treatment.
Bacteria evolve resistance over time, so breakpoints must be updated to match current data. Old breakpoints might call a bacterium susceptible when it is actually resistant. For instance, for the drug penicillin against Streptococcus pneumoniae, old breakpoints considered many strains susceptible. But after years of use, some strains became resistant. Updated breakpoints now correctly classify those strains as resistant. Using old breakpoints would lead doctors to prescribe penicillin, which would fail. Regular updates ensure accurate lab reports and effective treatment.
11. Compare how ADE in dengue differs from the normal protective role of antibodies.
Normally, antibodies bind viruses and block them from entering cells, which protects against infection. In antibody-dependent enhancement (ADE), antibodies do the opposite: they bind the virus but do not block it. Instead, they help the virus enter immune cells through Fc receptors. This increases viral replication and disease severity. In dengue, ADE occurs when antibodies from a past infection are not strong enough to neutralize a new virus type. So, instead of protection, the antibodies make the infection worse. This is a key difference from typical antibody function.
12. Why might a live attenuated vaccine give stronger immunity than an inactivated vaccine?
A live attenuated vaccine mimics a natural infection better because the weakened germ multiplies in the body. This stimulates both antibody and T cell responses, including memory cells. Inactivated vaccines do not multiply, so they mainly trigger antibodies and often need boosters. The live vaccine's replication also activates the innate immune system more strongly. As a result, live vaccines often provide lifelong immunity with fewer doses. However, they carry a small risk of causing disease in people with weak immune systems, so inactivated vaccines are safer for them.