Infectious Disease Control: Polio, Tuberculosis, Malaria, and Dengue

Comprehensive practice flashcards reviewing the epidemiology, transmission dynamics, life cycles, diagnostics, and intervention strategies for Poliovirus, Mycobacterium tuberculosis, Plasmodium (Malaria), and Dengue virus.

How many wild poliovirus types have been successfully eradicated worldwide?

Only two of the three wild poliovirus types have been eradicated.

What annual vaccination target and timeframe characterized India's polio elimination campaign?

India needed to vaccinate $170\text{ million}$ children per year and progressed from having half of all global cases to zero cases in $3\text{ years}$.

What intelligence operation in 2011 severely damaged public trust in polio vaccination campaigns in Pakistan?

The raid on Osama bin Laden, during which the CIA impersonated vaccinators to identify relatives of Bin Laden.

How did Boko Haram's activities in Nigeria in 2015 trigger a resurgence in polio transmission?

Boko Haram captured territory and cut off supplies, prompting infected individuals to flee into areas with low vaccination coverage.

Why did poliovirus Type 2 account for $86\%$ of all vaccine-derived polio cases?

A single nucleotide mutation in the live attenuated Type 2 vaccine allows it to revert to virulence more easily because it is less stable than Type 1 or Type 3.

What was the immunological rationale for switching from trivalent OPV to bivalent OPV?

Type 2 provoked the strongest immune response in trivalent OPV; removing Type 2 allowed Type 1 and Type 3 to generate immunity without competition.

In acute flaccid paralysis (AFP) surveillance, what is the distinction between screening and testing?

Screening identifies non-polio causes of AFP to rule out polio, whereas testing directly evaluates a proportion of AFP cases to confirm polio infection.

What is the typical cell division time of Mycobacterium tuberculosis?

It divides very slowly, requiring $15\text{--}20\text{ hours}$ to divide.

What specific names are given to extrapulmonary tuberculosis affecting the spine and the lymph nodes?

Tuberculosis of the spine is called Pott's disease, and tuberculosis of the lymph nodes is called scrofula.

What chemical component renders the cell wall of Mycobacterium tuberculosis waxy and hydrophobic?

Mycolic acids, which are long-chain fatty acids linked to peptidoglycan via polysaccharides.

What is the key epidemiological distinction between latent tuberculosis and asymptomatic tuberculosis?

Latent tuberculosis is non-replicating and non-infectious, whereas asymptomatic tuberculosis involves active bacterial shedding capable of transmission.

In the SIR model for tuberculosis, what mathematical equation defines the basic reproduction number $R_0$?

$R_0 = \beta \times L$, where $\beta$ is the transmission rate and $L = \frac{1}{\gamma}$ represents the average duration of infection.

Why does a long infectious period $L$ allow tuberculosis to sustain transmission despite a low transmission rate $\beta$?

A high value of $L$ offsets a low transmission rate $\beta$, allowing $R_0$ to remain between $1$ and $4.5$ and enabling a small critical community size to sustain infection.

Why can an active HIV coinfection cause a false negative on a tuberculin skin test?

HIV damages the immune system to the extent that it cannot mount the necessary delayed-type hypersensitivity reaction to the purified protein derivative.

What differentiates primary drug resistance from secondary drug resistance in tuberculosis?

Primary resistance occurs when an individual is initially infected with a resistant strain, whereas secondary resistance arises during therapy due to noncompliance, monotherapy, or low-quality antibiotics.

What are the four primary cellular pathways targeted by tuberculosis antibiotics?

Cell wall synthesis, energy metabolism, replication and transcription, and protein translation.

What are the efficacy rates of the BCG vaccine against tuberculosis infection in adults versus children?

BCG reduces infection by $20\%$ in adults and by $50\%$ in children, offering protection against severe miliary forms but limited protection against pulmonary disease.

What proportion of global malaria cases occur in sub-Saharan Africa?

$95\%$ of all cases.

Which two Plasmodium species cause the overwhelming majority of human malaria cases?

Plasmodium falciparum (predominant in Africa and responsible for most deaths) and Plasmodium vivax (predominant outside sub-Saharan Africa).

What are the primary feeding and breeding bionomics of the Anopheles mosquito vector?

Female Anopheles mosquitoes feed on human blood at night to develop eggs and breed primarily in shallow, still, fresh water.

In the malaria parasite life cycle, what parasite stage is injected by the mosquito, and what cells does it infect first?

Sporozoites are injected through mosquito saliva into the blood and immediately travel to hepatocytes in the liver to replicate.

What intraerythrocytic developmental sequence does Plasmodium follow before lysing red blood cells?

Merozoites develop into the ring stage, progress to nutrient-absorbing trophozoites, and mature into schizonts that rupture red blood cells.

What physiological event triggers malaria paroxysms (fevers, chills, and sweats) in the host?

The synchronous rupture of infected red blood cells and release of merozoites and pyrogens into the bloodstream.

Why does the Duffy negative phenotype confer protection against Plasmodium vivax?

The Duffy blood group receptor required by Plasmodium vivax merozoites to invade red blood cells is absent from the erythrocyte surface.

What quantitative reductions in malaria morbidity and mortality are achieved by WHO-recommended sporozoite vaccines?

They reduce uncomplicated malaria by $40\%$, severe malaria by $30\%$, and all-cause child mortality by $13\%$.

What biting behavior makes bed nets ineffective against Aedes mosquitoes transmitting dengue virus?

Aedes mosquitoes are daytime biters, unlike night-biting Anopheles mosquitoes.

Why are Aedes mosquitoes considered exceptionally efficient vectors of dengue virus?

They lay multiple batches of eggs and take multiple blood meals per egg batch, providing repeated opportunities to contract and transmit the virus.

What percentage of dengue cases present with clinical symptoms, and what fraction of those develop severe disease?

$25\%$ of dengue cases are symptomatic, and approximately half of those symptomatic cases ($12.5\%$ of total infections) progress to severe dengue.

What is the level of amino acid similarity among the four major dengue virus serotypes, and what problem does it cause?

The serotypes share $60\text{--}70\%$ amino acid similarity, leading to imperfect cross-immunity and increasing the risk of severe disease upon secondary infection.

What is the duration of viremia in a dengue-infected human, and how does it correlate with symptom onset?

Viremia lasts approximately $4\text{--}12\text{ days}$ and precedes the onset of clinical symptoms.