o Haemophilus influenzae, is also called Pfeiffer's bacillus or Bacillus influenza
o H. influenzae was the first free-living organism to have its entire genome sequenced.
o Most strains of H. influenzae are opportunistic pathogens
o They usually live in their host without causing disease, but cause problems only when other factors (such as a viral infection, reduced immune function or chronically inflamed tissues, e.g. from allergies) create an opportunity.
o They infect the host by sticking to the host cell using Trimeric Autotransporter Adhesins (TAA).
o Naturally acquired disease caused by H. influenzae seems to occur in humans only.
o Due to routine use of the Hib conjugate vaccine in the U.S. since 1990, the incidence of invasive Hib disease has decreased to 1.3/100,000 in children.
o However, Hib remains a major cause of lower respiratory tract infections in infants and children in developing countries where the vaccine is not widely used.
o Clinical features may include initial symptoms of an URTI mimicking a viral infection, usually associated with fevers, often low grade.
o The URTI then may progresses to a LRTI in a few days with features often resembling a wheezy bronchitis.
o Sputum is often grey to creamy in colour.
o The cough may persist for weeks without appropriate treatment.
o Clinical diagnosis of H. influenzae is typically performed by bacterial culture or latex particle agglutinations.
o Blood agar shows a satellite phenomenon around other bacteria.
o In Gram Stain, Gram-negative, rod shaped, with no specific arrangement.
o Fildes agar is the selective medium for isolation.
o The latex particle agglutination test (LAT) is a more sensitive method to detect H. influenzae than culture.
o Because the method relies on antigen rather than viable bacteria
o It also has the added benefit of being much quicker than culture methods.
Haemophilus influenzae produces beta-lactamases enzymes.
o Rickettsia rickettsii is a unicellular, Gram-negative coccobacillus
o It is most commonly known as the causative agent of Rocky Mountain spotted fever (RMSF).
o R. rickettsii is a non-motile, non-spore forming aerobic organism.
o They lack a distinct nucleus and membrane bound organelles.
o Their outer membrane is composed mostly of lipopolysaccharides.
o RMSF is transmitted by the bite of an infected tick while feeding on warm-blooded animals, including humans.
o Humans are considered to be accidental hosts in the Rickettsia–tick life cycle
o The life cycle of Rickettsia rickettsii is considered to be a complex one.
o Survival is dependent on both an invertebrate vector, (the hard tick- Family Ixodidae) and a vertebrate host (including mice, dogs, rabbits).
o Humans are considered to be accidental vectors
o Rickettsia rickettsii mostly affects canines and humans.
Three arthropod vectors in the United States have been identified in transmitting R. rickettsii to humans, causing the potentially fatal disease Rocky Mountain Spotted Fever. TheAmerican dog tick (Dermacentor variabilis), the Rocky Mountain Wood Tick (Dermacentor andersoni), and the Brown dog tick (Rhipicephalus sanguineus) can acquire Rickettsia rickettsiiin a number of different ways.
An uninfected mammal can become infected with Rickettsia rickettsii when eating food that contains the feaces of the infected tick. They can also be infected through the bite of an infected tick.
Humans acquire Rickettsia rickettsii infection from infected vectors. After getting bitten by an infected tick, rickettsiae are transmitted to the bloodstream by tick salivary secretions or, as mentioned previously, through contamination of broken skin by infected vector feces.
All these modes of transmission ensures the survival of Rickettsia in nature.
Rocky Mountain Spotted Fever.
o During the initial stages of the disease, the patient will experience fever, nausea, vomiting, and loss of appetite.
o The classic RMSF rash occurs in about 90% of patients and develops 2 to 5 days after the onset of fever.
o Rash appear as small, flat pink macules that develop peripherally on the patient's body, such as the wrists, forearms, ankles, and feet.
o Diarrhea, abdominal and joint pain, and pinpoint reddish lesions (petechiae) are observed during the late stages of the disease.
o Patients with severe infections may require hospitalization. They may become thrombocytopenic,
محتويات مواقع أعضاء هيئة التدريس بما فيها من نصوص وملفات وصور وأبحاث وأية مواد أخرى هي مسئولية عضو هيئة التدريس بالكامل بصفته صاحب الموقع وبما له من صلاحية مطلقة في الإضافة والحذف، وتخلي الجامعة مسئوليتها عن محتويات تلك المواقع.
جميع الحقوق محفوظة © عمادة تقنية المعلومات والتعليم عن بعد 2018م ــ 1440هـ.