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PA10.1-5,PA11.1-3,PA12.1-3 | Infections, Genetic & Environmental Disease — PBL Case

CLINICAL SETTING

The Chauhan family lives in a peri-urban resettlement colony on the outskirts of Nagpur, Maharashtra. The father, Santosh, 38 years old, works at a small bidi manufacturing unit and has been coughing for the past four months. The mother, Sushma, 35 years old, tends a small backyard plot where she raises pigs and uses untreated water from a local borewell for irrigation and cooking. Their eldest son, Arvind, 17 years old, began having generalised tonic-clonic seizures four months ago — he had been seizure-free his entire life until then. Their younger child, Priya, 4 years old, has been unwell for six months with recurrent respiratory infections, progressive abdominal distension, and a failure to gain weight despite eating well. The family presents together to the district hospital, referred from the PHC where the doctor noted 'something unusual about the whole family.' The PHC doctor has already noted: Santosh has raised, anaesthetic, hypopigmented patches on his left forearm and claw deformity of the right hand. Arvind's MRI brain (done at a private centre) shows multiple ring-enhancing cystic lesions in the cortex and basal ganglia. Priya weighs 11.5 kg at age 4 years and has marked hepatosplenomegaly.

Trigger 1: The Claw, the Seizures, and the Failing Child

Santosh: raised, pale, anaesthetic patches on forearm. Loss of pinch grip on right hand due to claw deformity. Slit-skin smear is requested. Arvind: first seizure at age 17 with no prior history. MRI shows 3–5 mm ring-enhancing cystic lesions scattered in cortex and basal ganglia; one shows a central hyperdense dot (scolex). History: family eats pork from home-raised pigs; water source is a shallow borewell. Priya: weight 11.5 kg (expected >16 kg); mid-upper arm circumference 10.2 cm; hepatosplenomegaly; recurrent chest infections; mother reports normal diet but no animal protein beyond eggs. Slit-skin smear from Santosh: AFB 2+ on Wade-Fite stain; globi visible.

DISCUSSION POINTS

Santosh's skin smear is positive for AFB with globi. What does this finding tell you about where his immune system sits on the tuberculoid-lepromatous spectrum, and what is the mechanism of nerve damage in his case?
Arvind's MRI shows ring-enhancing lesions with a central scolex. Walk through the life cycle of the organism responsible — how did Arvind acquire cysticercosis rather than intestinal taeniasis, and what is the host-parasite interaction in the brain that creates the ring-enhancing appearance?
Priya's growth measurements indicate severe acute malnutrition. Using her anthropometric data, classify her nutritional status and explain the pathophysiological mechanism of her hepatosplenomegaly in the context of protein-calorie malnutrition.
Looking at the whole family together: identify a common environmental exposure that could explain at least two of the three diagnoses, and explain the pathways by which that exposure leads to disease.

Click to reveal Trigger 2: Investigations, a Neighbour's Child, and a New Worry (discuss previous trigger first!)

Trigger 2: Investigations, a Neighbour's Child, and a New Worry

Santosh is classified as multibacillary leprosy (MB). Arvind's serum cysticercosis ELISA is reactive; CSF ELISA is also positive. Arvind's seizures are poorly controlled on phenytoin alone. A neighbour brings her 3-year-old daughter, Kavya, to the same clinic. Kavya's parents are first cousins; Kavya has developmental delay, generalised hypotonia, hepatosplenomegaly, and a cherry-red spot on fundoscopy. A bone marrow aspirate (done at the government medical college) shows large pale macrophages with 'crinkled tissue paper' cytoplasm. Meanwhile, Santosh's sister calls to say that Santosh's son from a previous pregnancy — an aborted fetus examined at the GMC — was found to have a large nuchal translucency and, on chromosomal analysis, trisomy 21.

DISCUSSION POINTS

Kavya's bone marrow shows large macrophages with crinkled cytoplasm. Name the condition, the deficient enzyme, the accumulated substrate, and explain how the pathological accumulation leads to her specific clinical findings.
The neighbour's consanguineous marriage increases the risk of this condition significantly. What is the inheritance pattern, and why does consanguinity increase recessive disease risk in a population?
Santosh's prior fetus had trisomy 21. Explain the mechanism of non-disjunction and how maternal age influences this risk. What prenatal screening options are available at district hospital level in India?
Classify the tissue reaction pattern in each of the three Chauhan family members (Santosh, Arvind, Priya) and explain how the dominant pattern in each case reflects the host immune response to the causative agent.

Click to reveal Trigger 3: Referral, Rehabilitation, and Root Causes (discuss previous trigger first!)

Trigger 3: Referral, Rehabilitation, and Root Causes

Santosh begins WHO multidrug therapy for MB leprosy (rifampicin, dapsone, clofazimine for 12 months). Arvind is started on albendazole and dexamethasone; seizure control improves. Priya is admitted for therapeutic feeding under the Nutrition Rehabilitation Centre programme. Kavya is referred for enzyme replacement therapy eligibility assessment. The district public health officer notes that Santosh works in a bidi manufacturing unit — spirometry done for occupational surveillance shows an obstructive pattern. The family's borewell water tests positive for faecal coliforms. An environmental health inspection identifies the pig pen adjacent to the family's kitchen. A nutrition survey in the colony finds 40% of children under 5 below the third centile for weight-for-height.

DISCUSSION POINTS

Santosh's spirometry shows an obstructive pattern from occupational tobacco dust exposure. Describe the pathological changes in the airways and lung parenchyma from chronic tobacco smoke inhalation, distinguishing between the mechanisms leading to chronic bronchitis versus emphysema.
The WHO MDT regimen Santosh is prescribed has been used for 40 years and dramatically reduced the leprosy burden in India. Explain the rationale for each drug in the regimen and why monotherapy would be inadequate.
The nutrition survey reveals a 40% burden of acute malnutrition in children under 5 in the colony. Distinguish kwashiorkor from marasmus in terms of pathogenesis, key clinical findings, and the specific biochemical deficiency that explains oedema in kwashiorkor.
From this family's story, map the environmental, social, and biological risk factors contributing to each disease in the family, and propose two specific public health interventions at the PHC level that would have the highest impact on reducing disease burden in this community.

Group Task Assignments

Group 1: Cysticercosis and malaria — mechanisms and pathology

Create a diagram showing the Taenia solium life cycle, clearly marking where human intestinal infection (taeniasis) diverges from human tissue infection (cysticercosis), and explain why neurocysticercosis causes ring-enhancing lesions on MRI.
Prepare a one-page summary of the pathogenesis of falciparum malaria, focusing on cytoadherence, rosetting, and the mechanism of cerebral malaria — contrast with the benign tertian malaria of P. vivax.

Competencies: PA10.1, PA10.2

Group 2: Leprosy spectrum and tissue reactions

Draw and label the tuberculoid-lepromatous spectrum of leprosy, correlating immune response (Th1 vs Th2), bacillary load, granuloma type, nerve damage, and skin lesion characteristics at each pole.
Explain the tissue reaction patterns used in infectious disease pathology (suppurative, granulomatous, cytopathic, necrotising, eosinophilic) and give one example of an Indian infectious disease for each pattern.

Competencies: PA10.3, PA10.4

Group 3: Lysosomal storage disorders and genetic disease

Construct a comparison table of Gaucher disease, Niemann-Pick disease, and Tay-Sachs disease covering: deficient enzyme, accumulated substrate, major organs involved, pathognomonic cell/finding, and availability of treatment.
Explain Knudson's two-hit hypothesis using retinoblastoma as the model, and discuss how this principle applies to other tumour suppressor genes in paediatric cancers.

Competencies: PA11.1, PA11.3

Group 4: Malnutrition, obesity, and environmental disease

Compare kwashiorkor and marasmus: present a case scenario for each, the key clinical features that distinguish them, the biochemical mechanism of oedema in kwashiorkor, and the WHO feeding protocol for severe acute malnutrition.
Describe the pathogenesis of metabolic syndrome, linking central obesity to insulin resistance, dyslipidaemia, hypertension, and non-alcoholic fatty liver disease — illustrate with a simple flow diagram.

Competencies: PA12.2, PA12.3

Group 5: COVID-19 and respiratory environmental disease

Summarise the pathogenesis of severe COVID-19, focusing on the ACE2 entry mechanism, the cytokine storm, and the three patterns of lung pathology (diffuse alveolar damage, organising pneumonia, acute fibrinous organising pneumonia).
Describe the pulmonary pathology of chronic tobacco smoke inhalation, distinguishing the lesions of chronic bronchitis, emphysema, and their co-existence in COPD — relate to Santosh's occupational spirometry findings.

Competencies: PA10.5, PA12.1

Learning Issues

Research these questions and bring your findings to the discussion.

[PA10.1] What is the life cycle of Plasmodium falciparum, and how do its unique properties (cytoadherence, knob formation, rosetting) cause the pathological features of cerebral and severe malaria?
[PA10.2] How does Taenia solium cause both intestinal taeniasis and disseminated cysticercosis, and what is the host immune response in the CNS that produces the ring-enhancing lesion on imaging?
[PA10.3] What determines where a patient falls on the tuberculoid-lepromatous spectrum, and how does the immune response at each pole produce different patterns of nerve and skin damage?
[PA10.4] What are the dominant tissue reaction patterns in infectious disease histopathology, and how can you use them to narrow a differential diagnosis from a biopsy?
[PA10.5] What is the pathogenesis of severe COVID-19, what are the key lung pathological findings, and what laboratory abnormalities characterise cytokine storm syndrome?
[PA11.1] What are the common numerical and structural cytogenetic abnormalities in childhood, how do they arise through non-disjunction or translocation, and what are the key clinical features of Down syndrome, Turner syndrome, and Klinefelter syndrome?
[PA11.2] What are the pathological features and molecular markers of neuroblastoma, Wilms tumour, retinoblastoma, Ewing sarcoma, and rhabdomyosarcoma, and how does Knudson's two-hit hypothesis apply to hereditary childhood tumours?
[PA11.3] What is the common pathogenic mechanism of lysosomal storage disorders, and what are the distinguishing features of Gaucher disease, Niemann-Pick disease (Type A), and Tay-Sachs disease in terms of enzyme deficiency, substrate, morphology, and prognosis?
[PA12.1] What are the pathological effects of tobacco smoke (chronic bronchitis, emphysema, carcinogenesis), and how do air pollution and occupational dust exposure lead to lung disease?
[PA12.2] What is the pathogenesis of protein-calorie malnutrition, how do kwashiorkor and marasmus differ pathophysiologically, and what are the consequences of vitamin deficiency disorders?
[PA12.3] How does central obesity lead to metabolic syndrome through insulin resistance, and what are the systemic pathological consequences including NAFLD, cardiovascular disease, and type 2 diabetes?