IMMUNOLOGY CASE STUDY: HIV

Presentation:

Jacob, a seven-month old infant has been suffering with diarrhea, thrush, and weight loss over the previous two months.

History:

Jacob was born a healthy infant. Jacob grew and developed normally during his first five months after birth. He received routine immunization with diphtheria, pertussis, tetanus and Hib vaccine at 2, 4, and 6 months without complications. Jacob was seen on a number of occasions by the family's doctor over the past two months. Previous blood work looked unremarkable.

At today's visit to the clinic, physical examination of Jacob revealed elevated temperature (38°C), pneumonia, a rapid heart and respiratory rate, diarrhea, a diaper rash and thrush. New blood work was ordered.

LABORATORY RESULTS

IMMUNOLOGY

Lymphocytes: Jacob Normal values for 7-month infant

Th (CD4) 0.08 x 109/L (1.7-2.8 x 109/L)

Tc (CD8) 1.0x 109/L (0.8-1.2 x 109/L)

(Jacob's levels of B lymphocytes were normal)

Serum immunoglobulins:

IgG 3.8 g/L (2.7-9.1 g/L)

IgM 0.5 g/L (0.3-0.8 g/l)

IgA 0.2 g/L (0.1-0.5 g/L)

Antibody to tetanus toxoid: Absent (Present)

MICROBIOLOGY

Blood Cultures: Negative Negative

Stool parasites Cryptosporidium Negative

Oral scrapings Candida albicans Negative

Case Questions

1. Why did Jacob have no microbial infections during his first five months after birth?

2. What microbe causes thrush, and where is it usually found? Why do infants often develop thrush? Under what circumstances do adults develop thrush?

3. What medications are typically prescribed to treat thrush?

4. Which arm of the immune system usually protects us from yeast infections?

5. Why was the test for tetanus toxoid antibodies negative?

6. What is Cryptosporidium and how is it treated?

7. What is Pneumocystis jiroveci? What medication is generally prescribed to treat Pneumocystis jiroveci pneumonia?
Noting the depressed ratio of helper-T (CD4 TH) cells/cytotoxic-T (CD8 TC) cells, the doctor ordered additional tests for HIV infection; and asked the parents to go for tests. Jacob's results were as follows:

1. Positive for HIV-1

2. Viral load of HIV was 120,000 copies of HIV-RNA per ml of plasma

Both parents were found to be positive for HIV-1 despite the absence of any outward signs of the infection. At the initial parental interview no risk factors for HIV infection had been identified. However, on re-questioning, the father admitted to intravenous drug use in his late teens. He also reported having had shingles soon after returning from his honeymoon a few years ago.

Case Questions:

8. What kinds of microbes are most likely to cause infection in patients with HIV?

9. What are "shingles", and what might explain their occurrence in the father's case?

10. What is the normal course of HIV infection without anti-retroviral therapy?

CASE GOAL:

Understand the role of opportunistic pathogens in causing disease in AIDS patients and understand how cell-mediated immunity typically protects against these microorganisms in immune competent individuals.

Adapted from Dalhousie University's "Family Crisis" case