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Diplomate American Board of Internal Medicine.
Diplomate American Board of Allergy and Immunology.

Michael Manning, MD, is board-certified in internal medicine as well as allergy and immunology. He provides a wide range of care to patients at Allergy, Asthma & Immunology, LTD, with two locations in Scottsdale and another in Gilbert, Arizona.

An Arizona native, Dr. Manning has very deep roots in the valley. His interest in allergy and immunology started when he was a patient in the office that he eventually joined.

He was very fortunate to start his career under the guidance of his childhood allergist and mentor, Dr. Hartley. This background gives Dr. Manning a unique insight and compassion for his

patients. Dr. Manning graduated with honors from Baylor University in Waco, Texas. He attended the University of Texas Health Science Center at Houston and pursued his internal medicine residency at St. Joseph’s Hospital and Medical Center in Phoenix. This was followed by an allergy and immunology fellowship at Scripps Clinic and Research Foundation in La Jolla, California.

Dr. Manning is a fellow of the American Academy of Allergy, Asthma, and Immunology and the American College of Allergy, Asthma, and Immunology. He is active on committees and leadership positions in both organizations. He is a diplomate of the American Board of Internal Medicine as well as the American Board of Allergy and Immunology. Dr. Manning is currently a member of the Board of Regents for the American College of Allergy, Asthma, and Immunology. He is a past president of the Western Society of Allergy, Asthma & Immunology.

His expertise includes allergies, asthma, sinusitis, food allergies, drug allergies, angioedema and hereditary angioedema, hives, contact dermatitis, aspirin and other drug desensitization, and immune deficiencies. Dr. Manning lectures throughout the United States, oversees a cutting-edge research department within his practice, and is active in educating medical students, residents, and allergy fellows.

For many years, Dr. Manning coached his sons in various youth sports. He was active on the boards of the different little league and high school sports. He has always had a love for running and enjoys completing half and full marathons with his daughter. He and his wife are also passionate about animal rescue.

Fatima Khan, MD, MBA, is board-certified by The American Board of Allergy and Immunology and the American Board of Internal Medicine. She works with the Allergy, Asthma & Immunology Associates team in Tampa and Brandon, Florida.

Dr. Khan grew up in New Jersey and moved to the Tampa Bay area in 2017. She received her medical degree from the University of Medicine and Health Sciences in New York City, New York, and her Master of Business Administration (MBA) from Columbia Southern University in Orange Beach, Alabama.

After graduating, Dr. Khan completed a dual residency in internal medicine and pediatrics at Newark Beth Israel Medical Center in Newark, New Jersey, while serving as chief resident in her last year. She completed her allergy and immunology fellowship at the Johns Hopkins All Children's Hospital in St. Peterspurgh, Florida, serving as chief fellow during her second year.

Dr. Khan has presented at the American Academy of Allergy, Asthma, and Immunology and the Clinical Immunology Society Annual Meetings.

She specializes in primary immunodeficiency disorders, penicillin drug allergy, asthma, eosinophilic esophagitis, and other immunologic diseases.

Diplomate American Board of Internal Medicine.
Diplomate American Board of Allergy and Immunology.

Board-certified in internal medicine, Aaron Davis, MD, is also a board-certified allergist and immunologist. He is dedicated to providing personalized care at Allergy, Asthma & Immunology, LTD, with two locations in Scottsdale and another in Gilbert, Arizona. He joined Allergy, Asthma & Immunology, LTD, in 2005 and serves as an investigator in clinical research trials.

Dr. Davis was born and raised in Richland, Washington. He graduated from Carroll College in Helena, Montana, with a Bachelor of Arts in biology. He completed medical school at St. Louis University School of Medicine.

Afterward, he moved to Arizona for his internal medicine residency at Mayo Clinic in Scottsdale and completed an allergy and immunology fellowship at Henry Ford Health Systems in Michigan.

He is a member of the Academy of Allergy, Asthma, and Immunology; American College of Allergy, Asthma, and Immunology; American Medical Association; Maricopa County Medical Society; and Arizona Allergy and Asthma Society. Dr. Davis is also a diplomate of the American Board of Internal Medicine and board-eligible by the American Board of Allergy and Immunology.

Dr. Davis is married to Kelly, an orthopedic physician assistant. He enjoys outdoor activities and traveling.

Erica Chen, MD, is a board-certified allergy and immunology specialist practicing at the Allergy and Asthma Specialist Doctors, Inc. location in West Covina, California. Her practice is centered around the treatment of allergic diseases, including nasal allergies and asthma.

Dr. Chen earned her medical degree from the Keck School of Medicine at the University of Southern California. Subsequently, she completed her combined internal medicine pediatric residency and allergy and immunology fellowship training at the Los Angeles County Hospital at the University of Southern California.

Dr. Chen is board certified by the American Board of Allergy and Immunology. She has contributed to multiple peer-reviewed scientific presentations and publications. She also holds numerous professional society memberships, including the American Academy of Allergy Asthma and Immunology and the American College of Allergy, Asthma and Immunology.

Dr. Chen is currently accepting new patients and looks forward to welcoming them to Allergy and Asthma Specialist Doctors, Inc.

Lori Davila, APRN, FNP-C, is a certified family nurse practitioner by the American Academy of Nurse Practitioners. She works with the Allergy, Asthma & Immunology Associates team in Tampa and Brandon, Florida.

Lori graduated from the University of South Florida in Tampa, Florida, with a Master of Science in Nursing in 2015. In her graduate program, she had diverse clinical experiences, including the Allergy/Immunology Clinic at the University of South Florida, John Hopkins All Children's Hospital in St. Petersburg, Florida, urgent care, and pediatric emergency care. 

Lori has years of experience as a registered nurse in the hospital setting. Since 2015, she has focused on treating patients with allergic diseases. She has been a sub-investigator in clinical research on chronic cough and food allergies. 

Lori also has extensive experience in nursing education and holds faculty positions at St. Petersburg College and Galen College of Nursing, both in St. Petersburg, Florida. She maintains membership in the American Association of Nurse Practitioners and the Sigma Theta Tau International Society of Nursing.

Lori is passionate about patient education and strives to ensure patients understand their diagnosis and treatment options to improve their quality of life.

RN, MSN Certified - ANCC Member of the American
Academy of Nurse Practitioners

Nurse practitioner Jean Nelson, RN, FNP-C, has been working at Allergy, Asthma & Immunology, LTD, for over 30 years. She provides compassionate care to patients at the practice’s two locations in Scottsdale and another in Gilbert, Arizona.

She received her associate’s degree in science and nursing at Iowa Central Community College and her Bachelor of Science in nursing at Arizona State University (ASU). She gained experience working as a registered nurse alongside Drs. Hartley, Romero, and Manning at Allergy, Asthma & Immunology, LTD.

Jean later completed her family nurse practitioner curriculum and her Master of Science at the ASU Edson College of Nursing and Health Innovation. She graduated summa cum laude and was recognized as a Graduate Scholar of the Year in 2003. Her applied research project assessed the management of adult asthma through support and education.

As a family nurse practitioner, Jean serves as a primary care provider within the clinic. She gathers complete histories, performs physical exams, orders and interprets diagnostic tests, prescribes medications, and collaborates with patients to formulate a treatment plan and optimized well-being.

Jean is a patient advocate who focuses on health promotion and wellness with patients. She embraces the value of being proactive rather than reactive in health care planning and management. She enjoys educating not only her patients but also health care providers nationwide. Jean travels extensively throughout the United States lecturing about various diseases and the latest in medical treatments.

She is proud to serve as an active board member of the Arizona Asthma Coalition and is the chairman of the planning committee for the annual Asthma & Allergy Clinical Conference in Phoenix. She is certified by the American Nurses Credentialing Center and a member of the American Academy of Nurse Practitioners.

Jean is the mother of three children and is an accomplished pianist and organist.

Joshua Ang, DO, is a board-certified allergy and immunology specialist dedicated to helping patients at Allergy and Asthma Specialist Doctors, Inc., in Pasadena and West Covina, California. He provides personalized care for a wide range of concerns, including seasonal and environmental allergies, asthma, eczema, food allergies, sinus issues, and immune system conditions.

Dr. Ang earned his medical degree from the Philadelphia College of Osteopathic Medicine and completed his Internal Medicine Residency at Midwestern University – Mountain Vista Medical Center. He then completed his Allergy and Immunology Fellowship at Larkin Community Hospital in Miami, where he served as chief fellow.

Certified by both the American Osteopathic Association for Adult and Pediatric Allergy and Immunology and the American Board of Internal Medicine, Dr. Ang stays current on the latest treatments and research. He is an active member of professional organizations, including the American Academy of Allergy, Asthma & Immunology and the American College of Allergy, Asthma & Immunology.

Dr. Ang is passionate about working closely with his patients to create customized treatment plans that improve quality of life and help them breathe easier every day.

Dr. Daniel A. Steigelman, M.D., earned his Bachelor of Science in Bioengineering from the University of California, Berkeley, before receiving his medical degree from the Uniformed Services University of the Health Sciences (USUHS) in Bethesda, Maryland. He completed his post-graduate medical training through the San Antonio Uniformed Services Health Education Consortium (SAUSHEC), where he finished both his residency in Pediatrics and his specialized fellowship in Allergy and Immunology.

Dr. Steigelman is double board-certified, holding credentials as a Diplomate of the American Board of Allergy and Immunology and a Diplomate of the American Board of Pediatrics. These certifications qualify him to diagnose and manage allergic, asthmatic, and immunologic conditions in both children and adults. Alongside his clinical work, he has stayed active in medical education, serving as an Associate Professor of Pediatrics and Medicine at USUHS.

Before transitioning to private practice, Dr. Steigelman spent his career as an active-duty physician in the United States Air Force. During this time, his leadership roles included serving as the Consultant to the USAF Surgeon General for Allergy and Immunology and directing SAUSHEC's Transitional Year residency program. Following his retirement from active duty in April 2026, he joined Allergy and Asthma Specialist Doctors, Inc., providing dedicated care to patients in the Los Angeles community.

Chad W. Mayer, DO, FAAAAI, FAAP, offers comprehensive care at Allergy & Asthma Institute of Southeast Michigan in Farmington Hills, Michigan. With certification from the American Board of Allergy and Immunology and the American Board of Pediatrics, Dr. Mayer is uniquely qualified to treat children and adults.

Dr. Mayer is a leader in oral immunotherapy (OIT), serving as one of the first doctors in the country to offer this life-changing treatment for people with food allergies.

After receiving a Bachelor of Arts degree at Albion College in Albion, Michigan, Dr. Mayer graduated from Michigan State University College of Human Medicine in Grand Rapids, Michigan.

He continued his training at Henry Ford Hospital in Detroit, Michigan, where he completed his pediatric residency and was honored to serve as the pediatric chief resident. Dr. Mayer received pediatric and adult allergy/immunology fellowship training at Louisiana State University in Baton Rouge, Louisiana.

Before entering private practice, Dr. Mayer was the Associate Pediatric Program Director at Bi-County Community Hospital in Warren, Michigan. He has co-authored numerous articles published in prestigious medical journals, exploring essential topics such as granulomatous disease in infants and the management of food allergies. 

Dr. Mayer is affiliated with five hospitals: Detroit Medical Center Huron Valley-Sinai Hospital in Commerce Township, Michigan, Ascension Providence Hospital in Novi and Southfield, Michigan, Beaumont Hospital in Royal Oak, Michigan, Trinity Health Oakland Hospital in Southfield, Michigan, and McLaren Oakland Hospital in Pontiac, Michigan.

Marine Demirjian, MD, is a board-certified allergy and immunology specialist at Allergy and Asthma Treatment Center in Glendale, California. Her practice emphasis is centered around the treatment of allergic diseases. 

A native of Los Angeles, Dr. Demirjian earned her medical degree from the University of California, Los Angeles School of Medicine. Subsequently, she completed her internal medicine residency at the Ronald Reagan UCLA Medical Center and allergy-immunology fellowship at the VA Greater Los Angeles Healthcare System and Children's Hospital Los Angeles.

Dr. Demirjian is board certified by the American Board of Allergy and Immunology as well as the American Board of Internal Medicine. She holds numerous professional society memberships, including the American Academy of Allergy Asthma and Immunology, American Contact Dermatitis Society, and the American College of Allergy, Asthma, and Immunology. She also worked an associate clinical instructor of allergy and immunology at UCLA’s Department of Medicine for ten years. 

As an allergy specialist, Dr. Demirjian believes that identifying and eliminating environmental factors is critical to controlling allergic diseases. In addition, with allergy injections, she can help patients achieve tolerance to their allergic triggers so they can live their lives free of allergy symptoms.

National Commission on Certification of Physician
Assistants, Board Certified, 1998

Rachael Stillwagon, MS, PA-C, is a caring physician assistant at Allergy, Asthma & Immunology, LTD, with two locations in Scottsdale and another in Gilbert, Arizona.

Rachael was born in Iowa and raised in Iowa and Wisconsin. She received her Bachelor of Arts in biology and psychology from the University of Iowa.

She then earned her Master of Science in physician assistant studies at Rosalind Franklin University of Medicine and Science (RFU), formerly Finch University of Health Sciences. Rachael practiced internal medicine in Chicago for two years and co-taught a pharmacology class at RFU with her husband, Chad, a pharmacist.

In 2000, Rachael began working in the specialty of allergy and asthma, and has been passionate about the field ever since. In 2002, she and her husband moved to Scottsdale, where she continued her work. Rachael is a member of multiple allergy associations locally and nationally. She has served on various professional committees and currently lectures locally on atopic dermatitis.

As a physician assistant, Rachael serves as a primary care provider within the clinic. Her responsibilities include history and physical examinations, ordering and interpreting diagnostic tests, prescribing medications, and patient follow-ups. She works personally with each patient to formulate a treatment plan and ensure the best possible care.

Rachael and her husband have three children, all born in Scottsdale. She enjoys running, spending time with friends and her large family, volunteering with her children for Boys Team Charity and the National Charity League, as well as various projects at their schools. She loves watching her children participate in their sporting events and other activities!

Diplomate American Board of Internal Medicine.

Diplomate American Board of Allergy and Immunology.

Hiral Thakrar, MD, is an allergist and immunologist at Allergy, Asthma & Immunology, LTD, with two locations in Scottsdale and another in Gilbert, Arizona.

She manages adult and pediatric conditions, such as allergies of the nose and skin, hives, asthma, food allergies, and drug allergies. She is board certified in both Internal Medicine and Allergy and Immunology.

Dr. Thakrar was born and raised in Tanzania, East Africa, and attended the University of California, Los Angeles for her undergraduate studies.

She then pursued her medical degree at Ross University School of Medicine and completed her internal medicine residency at St. Joseph’s Hospital and Medical Center in Phoenix, Arizona. There, she was the Wellness Chief and participated in the Wellness and Integrative Medicine Committee. She completed her fellowship in allergy and immunology at Scripps Clinic in San Diego, California.

She is a member of the Western Society of Allergy, Asthma & Immunology, American Academy of Allergy, Asthma & Immunology (AAAAI), and American College of Allergy, Asthma, and Immunology. She has been a mentor for future aspiring allergists in medical school and residency for the past two years as a Chrysalis mentor for AAAAI.

Dr. Thakrar has conducted her research in Dupilumab and its effects on patch testing for allergic contact dermatitis, alcohol reactivity in AERD, penicillin allergy, epitope binding, and single sequencing with peanut allergy. Her special interests are asthma, aspirin-exacerbated respiratory disease (AERD), food allergies, and contact dermatitis. She takes an integrative medicine approach to all these diseases.

Dr. Thakrar is also the allergy residency director of two residency programs in East Valley. She mentors current residents and fellows in the field of allergy, asthma & immunology. She isnow also the co-director of wellness for residents at the residency programs. 

Dr. Thakrar is married and loves to spend time with her two beautiful children. In her free time, she enjoys yoga and meditation, traveling, and hiking, and participating in Indian cultural events.

Colleen Sabella, MD, is a board-certified allergist and immunologist at Allergy, Asthma & Immunology Associates team in Tampa and Brandon, Florida, with specialized training in diagnosing and treating a wide range of allergic and immune-related conditions in both children and adults.

She earned her medical degree from Penn State College of Medicine and completed her pediatric residency at Phoenix Children's Hospital. Dr. Sabella went on to complete a competitive fellowship in Allergy and Immunology at the University at Buffalo.

Before relocating to Tampa, Dr. Sabella practiced at a major academic medical center in Portland, Oregon, where she taught medical students and residents and served as the founder and medical director of the allergy clinic at the Portland Veterans Affairs Medical Center.

Dr. Sabella brings a patient-centered approach to the Allergy, Asthma, and Immunology Associates of Tampa Bay, with clinical interests, including food allergies, eczema, asthma, chronic hives (urticaria), angioedema, and drug allergies. She is passionate about improving the quality of life for her patients through personalized care plans and long-term disease management.

Originally from Erie, Pennsylvania, Dr. Sabella enjoys spending time outdoors with her husband and two sons, especially hiking and visiting the beach. She is also a proud supporter of the Penn State Nittany Lions.

Constantine K. Saadeh, MD, FAAAAI, FACP, FACR, is a board-certified internal medicine specialist serving patients at Allergy A.R.T.S. in Amarillo, Texas. 

In addition to internal medicine, Dr. Saadeh has fellowships and additional board certifications in allergy/immunology, rheumatology, and gerontology. Although that may seem an unusual combination of interests, he chose these specialties because they complement one another. 

Many arthritic conditions stem from disorders of the autoimmune system, such as rheumatoid arthritis, lupus, polymyositis, and many other conditions. Most conditions treated by an allergist/immunologist also involve the immune system. Knowledge of the pathology surrounding both specialties enhances the understanding of the immune system as a whole. 

Since many patients with arthritic conditions are part of the elderly population and metabolize medications differently than others, understanding the physical differences allows him insight into differing treatment approaches for different age groups. 

Dr. Saadeh is “grandfathered” in allergy/immunology and rheumatology. That means he is not required to recertify through the stringent testing recertification requirements. Nonetheless, Dr. Saadeh opts to voluntarily re-certify. His academic background has driven him to reinvest practice revenues into cutting-edge diagnostic equipment and the well-trained personnel it takes to operate it. 

Allergy A.R.T.S. is a reflection of his desire to provide the most comprehensive and well-studied approaches to treatment.

Rama R. Yerramsetti, MD, is an adult and pediatric allergy specialist at Texas Multi-Specialty Group at Texas Multi-Specialty Group with offices in Cypress and Houston, Texas. Dr. Yerramsetti is dual board-certified in allergy and immunology and pediatrics. For him practicing medicine is about more than just relieving symptoms. 

Dr. Yerramsetti is committed to spending time with his patients not only to properly diagnose and treat their conditions but also to make sure they understand their allergy diagnosis.

He began his path to his medical career as a medical student at Siddhartha Medical College in India. Upon graduation, he came to the United States to continue his studies as a resident in pediatrics at Rutgers Biomedical and Health Sciences. Dr. Yerramsetti completed his postdoctoral clinical training with a fellowship in allergy and immunology at UCI.

Dr. Yerramsetti’s patients often acknowledge him for his caring, compassionate, and attentive nature. When he isn’t busy helping his patients, Dr. Yerramsetti is active in the Texas Medical Association and the Harris County Medical Society.

Srinagesh Paluvoi, MD, FAAP, FACAAI, and the staff at Allergy & Asthma Affiliates in Landsdowne and Gainesville, Virginia, have built a solid reputation among their patients, community, and medical professionals in the field. They’re known and respected for providing compassionate, personalized allergy and immunology care that’s grounded in evidence-based science, time-tested treatments, and age-appropriate goals. They stay on the cutting edge of emerging medical technology so they can provide exceptional care to patients of all ages.

Patients with any type of allergy receive precise allergy testing and outstanding treatments in a state-of-the-art facility. Dr. Paluvoi helps patients with seasonal, year-round, food, stinging insect, medication, and chemical allergies. He and his team work closely with patients who have eczema, chronic sinusitis, and asthma, ensuring they have effective treatments so they can enjoy an active life. Dr. Paluvoi also specializes in complex immunodeficiency diseases in children and adults.

When patients choose Allergy & Asthma Affiliates, they become partners with a medical team dedicated to treating each person with dignity, respect, kindness, and courtesy. Patients are embraced by the team’s spirit of harmony and cooperation, so they feel relaxed and know they’ve found allergy, asthma, and immune deficiency disease care that rises above standard protocols to deliver optimal therapies and results.

At Allergy and Asthma Specialists of Greater Washington, patients of all ages can meet with Bridget Joseph, MD, who has been practicing in allergy and asthma specialties since 1992. Dr. Joseph cares for patients at the Warrenton, Culpeper, and Front Royal, Virginia, clinics.

After excelling through her undergraduate studies, Dr. Joseph went on to earn her medical degree from Calicut Medical College in India. She then completed her residency training in internal medicine at Charleston Area Medical Center in West Virginia. Dr. Joseph is currently board-certified in internal medicine through the American Board of Internal Medicine.

Dr. Joseph enjoys giving back to communities in need and has been an integral part of several mission trips to Haiti. She also spent time training at the Washington DC Veterans Affairs Medical Center and continues to venture out to care for patients of all ages who need medical care.

Because Dr. Joseph believes in staying at the top of her specialty in allergy and asthma care, she continues her education and training as much as possible. When she isn’t busy caring for patients, she enjoys hiking and playing tennis.

Dr. Joseph is available in the Warrenton, Culpeper, and Front Royal offices.

Robert McDermott, MD, is a board-certified allergist and immunologist and the founder of Allergy, Asthma & Immunology of the Rockies, with offices in Basalt and Glenwood Springs, Colorado. The practice has been proudly serving communities across Colorado since 2008. A lifelong Colorado native, Dr. McDermott combines local insight with advanced medical training to provide expert, personalized care for patients of all ages.

He earned his medical degree and completed his internal medicine residency and allergy/immunology fellowship at the University of Colorado and National Jewish Health, two institutions known nationally for excellence in respiratory and immune-related care. With decades of experience, Dr. McDermott offers comprehensive treatment for conditions including seasonal and environmental allergies, asthma, eczema, food allergies, and immune deficiencies.

Known for his thoughtful and thorough approach, Dr. McDermott takes time to listen to each patient’s concerns, review their medical history, and develop tailored treatment plans designed to improve health and quality of life. He stays at the forefront of allergy and immunology advancements through his involvement with the American Academy and College of Allergy, Asthma & Immunology, as well as local medical and civic organizations.

Outside the clinic, Dr. McDermott enjoys skiing, hiking, and fishing with his family—activities that deepen his connection to the Colorado lifestyle and the environmental factors that impact his patients. His dedication to individualized care, combined with his deep roots in the community, makes him a trusted partner in long-term allergy and asthma management.