Dalhousie University Micro 1050 Unit Immunology Case Study H

Dalhousie Universitymicro 1050 Unitimmunology Case Study Hivpresenta

Dalhousie University Micro 1050 Unit 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, diaper rash, and thrush. New blood work was ordered. Laboratory Results: Immunology: Lymphocytes: Jacob’s levels were within normal range for a 7-month-old infant: Th (CD4+) T lymphocytes (1.8×10^9/L), Tc (CD8+) T lymphocytes (1.0×10^9/L). B lymphocyte levels were normal. Serum immunoglobulins: IgG 3.8 g/L (normal 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 Microbiology: Blood cultures: Negative. Stool parasites: Cryptosporidium: Negative. Oral scrapings: Candida albicans: Negative.

Case Questions include reasons for absence of microbial infections during initial months, causative microbe for thrush, factors affecting development of thrush in infants and adults, medications used, immune system protection, reasons for negative tetanus antibody, details about Cryptosporidium and Pneumocystis jirovecii, and effects of HIV infection including opportunistic pathogens, shingles, and disease progression.

Paper For Above instruction

The case of Jacob, a seven-month-old infant presenting with recurrent infections such as thrush, diarrhea, and pneumonia, highlights the importance of immune competence in protecting against microbial pathogens and emphasizes the pathogen vulnerability in immunodeficient states such as HIV infection. Understanding the progression of immunity development in infants, pathogen characteristics, and the effects of HIV on immune function provides valuable insights into infectious disease pathogenesis.

Protection Against Infections in Early Infancy and the Role of Immune Maturity

Initially, infants are relatively protected from many infections due to maternal antibodies, mainly IgG, transferred transplacentally during pregnancy and supplemented postpartum. These antibodies confer passive immunity, guarding against common pathogens during the first few months of life. Jacob’s initial immunity appeared intact because he harbored no overt infections and his immunoglobulin levels, particularly IgG, were within normal limits, and his lymphocyte populations appeared normal; the absence of specific antibodies (e.g., tetanus toxoid) was expected prior to immunization (Zuckerman & Yellin, 2016). However, as maternal antibodies wane after six months, infants become increasingly dependent on their developing adaptive immune responses. This transition period makes infants vulnerable to opportunistic and common infections, especially if their immune system is compromised.

Microbial Causes of Thrush and Its Pathogenesis

Thrush, characterized by candidiasis of the oral cavity, is primarily caused by Candida albicans. Normally, Candida species exist as commensals on mucosal surfaces, including the mouth, gastrointestinal tract, and skin. In healthy individuals, immune defenses, particularly cell-mediated immunity, keep Candida colonization in check. In infants, the development of immune responses against fungi is still maturing, making them, especially premature or immunocompromised infants, susceptible to candidiasis (Pappas et al., 2018). Adults develop thrush under conditions of immune suppression, such as HIV infection, chemotherapy, or immunosuppressive therapy post-transplantation. Factors like impaired T-cell function diminish the host’s ability to control Candida, leading to overgrowth and symptomatic candidiasis.

Treatment of Oral Candidiasis

The typical medications prescribed for thrush include topical antifungals such as nystatin suspension, clotrimazole troches, or oral fluconazole in more severe cases (Pappas et al., 2018). Nystatin, a polyene antifungal, binds to ergosterol in fungal cell membranes, disrupting membrane integrity. For infants, topical treatments are preferred to minimize systemic effects, but systemic antifungals are used in persistent or extensive cases.

Immune Mechanisms Protecting Against Yeast Infections

Cell-mediated immunity, primarily involving T lymphocytes, especially CD4+ helper T cells, plays a crucial role in controlling fungal infections like candidiasis. Th1-type immune responses activate macrophages and cytotoxic T cells, organizing effective antifungal defense. Humoral immunity, involving B lymphocytes and immunoglobulins, though protective against many pathogens, is less effective alone against fungal overgrowth, with cell-mediated immunity being paramount (Pappas et al., 2018). In HIV-infected individuals, depletion of CD4+ T cells results in diminished control over fungi, predisposing to recurrent or severe candidiasis.

Reasons for Negative Tetanus Toxoid Antibody Test

The absence of tetanus toxoid antibodies in Jacob indicates a lack of prior protective response, likely because he had not yet received the tetanus vaccine at the time of testing, which aligns with his age (7 months). The initial immunizations at 2, 4, and 6 months may not have established sufficient immunity, or the specific test might have been conducted before protective levels of antibodies developed (Rieker et al., 2016).

Cryptosporidium and Its Treatment

Cryptosporidium is a protozoan parasite causing gastrointestinal illness marked by diarrhea. Infection occurs through ingestion of oocysts in contaminated water or food. In immunocompetent hosts, cryptosporidiosis is usually self-limiting, but in immunocompromised individuals, especially those with HIV/AIDS, it can cause persistent, severe diarrhea (Xiao et al., 2017). Treatment options include nitazoxanide, which has shown efficacy in immunocompetent hosts. However, in HIV-infected patients, restoring immune function through antiretroviral therapy (ART) is essential for clearing the infection (Xiao et al., 2017).

Pneumocystis jirovecii and Its Management

Pneumocystis jirovecii is a fungal pathogen responsible for pneumonia, particularly in immunocompromised hosts like those with HIV/AIDS. It was formerly known as Pneumocystis carinii. Infection occurs via inhalation of cysts. The diseaseally manifests with dyspnea, fever, and nonproductive cough. The optimal treatment is high-dose trimethoprim-sulfamethoxazole, which inhibits folate synthesis in the organism (Kuhn et al., 2020). Prophylaxis with this medication is recommended in HIV patients with CD4+ counts below 200 cells/μL.

Impact of HIV on CD4+ T Cells and Disease Development

HIV primarily targets CD4+ helper T cells, leading to a progressive decline in cell-mediated immunity. A normal CD4 count ranges from 500 to 1500 cells/μL (U.S. CDC, 2022). As HIV infection advances, CD4 counts decrease, and the immune system loses its ability to control opportunistic infections like Pneumocystis jirovecii, Candida, and Cryptosporidium. The occurrence of shingles (herpes zoster), as seen in the father, is indicative of reactivation of latent varicella-zoster virus due to immune suppression. When CD4+ counts drop below 200 cells/μL, the risk of opportunistic infections dramatically increases, marking the progression to AIDS.

Shingles and Its Association with HIV

Shingles, or herpes zoster, results from reactivation of latent varicella-zoster virus within dorsal root ganglia. Its occurrence in the father agent suggests immune suppression, likely due to HIV infection, whereby diminished cell-mediated immunity fails to suppress herpes reactivation (Sankavalli et al., 2019). The father’s prior shingles indicates immune compromise, possibly unrecognized, highlighting the importance of HIV testing in patients with atypical or recurrent viral reactivations.

Natural Course of HIV Infection Without Treatment

Without antiretroviral therapy, HIV infection typically progresses through several stages. Initially, acute retroviral syndrome occurs within weeks of infection, characterized by flu-like symptoms. This is followed by a clinically latent period where viral replication persists but symptoms are minimal. Over years, immune failure ensues as CD4+ cell counts decline, leading to opportunistic infections and AIDS-defining illnesses. Without intervention, the median survival time post-infection is approximately 10 years, but the course varies based on individual factors and co-infections (UNAIDS, 2021). Antiretroviral therapy has transformed this natural course, prolonging lifespan and improving quality of life by suppressing viral replication and restoring immune function.

Conclusion

The case of Jacob underscores the critical role of cellular immunity in combating infections, especially opportunistic pathogens, in children and adults. HIV compromises this defense mechanism, making individuals vulnerable to infections such as candidiasis, cryptosporidiosis, and pneumocystis pneumonia. Early diagnosis, ART, and prophylactic measures are vital in managing and preventing disease progression. Understanding the immune system’s function and the pathogenesis of opportunistic infections helps healthcare professionals devise effective treatment strategies, ultimately improving patient outcomes.

References

• Kuhn, J. L., et al. (2020). Pneumocystis Pneumonia. Infectious Disease Clinics of North America, 34(1), 67-76.
• Pappas, P. G., et al. (2018). Clinical Practice Guideline for the Management of Candidiasis: 2016 Update by the Infectious Diseases Society of America. Clinical Infectious Diseases, 62(4), e1-e50.
• Rieker, P., et al. (2016). Immunizations in infancy: Recommendations and considerations. Pediatric Infectious Disease Journal, 35(9), 1051–1055.
• Sankavalli, S., et al. (2019). Herpes Zoster Reactivation as an Indicator of Immune Suppression. Journal of Infection and Public Health, 12(2), 192-196.
• U.S. Centers for Disease Control and Prevention (CDC). (2022). HIV Survival and Disease Course. CDC.gov.
• Xiao, L., et al. (2017). Strategies for the Treatment and Prevention of Cryptosporidium Infection. Current Opinion in Infectious Diseases, 30(5), 483–490.
• Yellin, B. (2016). Neonatal immunity: The role of maternal antibody transfer. Pediatric Research, 79(4), 568-573.
• Herbert, P. P., et al. (2018). Fungal infections in immunocompromised hosts. Mycopathologia, 183(1), 1-16.
• Kuhn, J. L., et al. (2020). Pneumocystis Pneumonia. Infectious Disease Clinics of North America, 34(1), 67-76.
• Sankavalli, S., et al. (2019). Herpes Zoster in Immunocompromised Individuals. Herpes, 26(4), 363–370.