Polio, Cystic Fibrosis and Hypothyroidism

Polio Poliomyelitis, commonly referred to as polio is cause by acute viral infection from its causative agent, the poliovirus. The virus belongs to the enterovirus family and consists of a naked RNA strand (Kumar, Abbas & Fausto, 2004, p. 364). The route of spread is fecal oral, similar to most other members of the enterovirus class. The initial infection occurs in the mouth and throat, resulting in the secretion of the virus from the salivary glands and its subsequent entry into the gastrointestinal tract.
Virus multiplication occurs in the mucosa of the intestines and in lymph nodes, a process that causes symptoms associated with a transitory viremia. Most polio infections do not surface clinically; about 1% of infected individuals suffer the consequences of central nervous invasion by the virus (Kumar, Abbas & Fausto, 2004, p. 364). This invasion first manifests as meningeal irritation. But the most debilitating effects are seen when it proceeds to the spinal cord, infecting the motor neurons.
This invasion causes wasting of muscles and loss of reflexes; a disability that persists for the rest of the patient’s life (Kumar, Abbas & Fausto, 2004, p. 1374). Two types of vaccines have been developed and successfully administered for the poliovirus. The Salk type is fixed in formalin and contains killed specimens of all three major strains of the poliovirus; more commonly, the oral Sabin type vaccine is used which contains live attenuated virus specimens of all three strains as well.

The success of the vaccine in nearly eliminating the virus from developed countries and from most of the developing world is based on the fact that this virus, like smallpox, only infects humans. Additionally, it is shed from an infected individual for a small period of time; it does not change its antigenic molecular makeup through mutations and the vaccine confers lifetime immunity (Kumar, Abbas & Fausto, 2004, p. 364). Cystic Fibrosis Cystic fibrosis is one of the most widespread genetic disorders, especially in the Caucasian populations (Kumar, Abbas & Fausto, 2004, p.489).
It is an autosomal recessive disease, therefore most carriers of the abnormal allele present with no symptoms. The prime underlying cause of this condition is a mutation on the chromosome 7, in a gene that has been named cystic fibrosis transconductance regulator gene. This gene codes for a protein that forms a transmembrane channel that actively regulates the crucial transfer of electrolytes across the membrane, notably the chloride ion. The rate and volume of this transport is also modulated by intra- and extra-cellular signals (Kumar, Abbas & Fausto, 2004, p.490).
Once electrolyte content of the secretions is compromised, it leads to varying water content in extracellular compartments and causes a wide range of debilitating symptoms in different tracts. The most common clinical presentation is respiratory distress in newborn babies. The extremely viscid secretions in the lungs result in recurrent and severe respiratory infections. Moreover, the increased tissue resistance of the lungs results in an increased right-heart workload, which may cause right heart failure.
These complications are the most common cause of cystic fibrosis-related deaths in USA. The pancreas is also frequently involved; the exocrine part is hit the hardest. This insufficiency results in protein and fat malabsorption which leads to other complications including insufficient absorption of fat-soluble vitamins, and edema due to decreased levels of plasma proteins (Kumar, Abbas & Fausto, 2004, p. 494-495). There have been several advances in the management of this disease.
Improved control of respiratory infections and lung transplant has given encouraging results; children and young adults who have had both their lungs transplanted have a survival rate of 70%. Heart, liver, and pancreas transplants have also shown favorable results (Kumar, Abbas & Fausto, 2004, p. 495). Hypothyroidism Hypothyroidism is defined as below normal levels of production or action of the thyroid hormone (Kumar, Abbas & Fausto, 2004, p. 1167). The thyroid hormone has widespread effects on the body in regard to regulation of the metabolic rate of all tissues.
Hypothyroidism is of three types: primary, resulting innate problems of the thyroid; secondary, due to improper functioning of the pituitary gland; and tertiary, caused by a deficiency of the hypothalamus. The most common type of hypothyroidism in iodine-sufficient areas is primary, resulting from immune reaction to the thyroid gland itself, a condition known as Hashimoto thyroiditis. In this disorder, the immune system causes cell death in thyroid tissue either by direct cell toxicity or by antibody-mediated reactions (Kumar, Abbas & Fausto, 2004, p. 1167-1170).
An antibody against the thyroid stimulating hormone receptor, which resides on the cell surface of thyroid tissue, is most frequently found in patients of Hashimoto thyroiditis. Clinically, this disorder presents as a swelling of the thyroid with no symptom of pain; the swelling is commonly diffuse and equal in size and shape on both sides (Kumar, Abbas & Fausto, 2004, p. 1170). The disease progresses slowly and insidiously, manifested by lack of energy and dullness, often mistaken for depression. Cognitive functions are also impaired and obesity has been reported.
Decreased sympathetic activity causes gastrointestinal problems. Since the thyroid hormone directly regulates cardiac calcium influx, a decrease in cardiac output is seen, followed by lowered stamina in the patient (Kumar, Abbas & Fausto, 2004, p. 1168). Diagnosis is made by serological investigations, TSH levels in serum being the most sensitive indicator of thyroid function; TSH levels are actually high in response to lowered thyroxine levels in primary hypothyroidism. Levothyroxine is the drug of choice for such patients (Kumar, Abbas & Fausto, 2004, p. 1169).