belongs to the subfamily Ponerinae, a species that is widely distributed in tropical and subtropical regions worldwide. It is believed to be indigenous to Southeast Asia, but has been reported from all of the Arab Gulf countries including Kuwait, Qatar, the United Arab Emirates, Oman, Yemen and Saudi Arabia.4
In Saudi Arabia it seems to prefer areas of human habitation. Although the ant is a scavenger in nature, it stings human beings as a defensive behavior.5
Recently, several anaphylactic cases following black (samsum) ant stings were reported in local clinics in Saudi Arabia, some of them critical.6
This ant has been observed around and inside houses and in hospital residence areas in many locations in the Al Riyadh region. The risk to humans from a particular species probably depends on complex interactions between the likelihood of human contact, insect aggression, efficiency of the venom delivery apparatus, and venom allergenicity.
The most important morphological features of this ant are the large eyes and mandibles with a dorsolateral pit, and the presence of a deep mesopropodal furrow (). It does not bite; instead, it injects venom through a stinger (), like fire ants and other Hymenoptera. The mechanism of the reaction to the sting of the black ant Pachycondyla sennaarensis
is a type I IgE-mediated hypersensitivity and the diagnosis can be confirmed by skin tests and specific IgE determination.7,8
Photograph of Pachycondyla sennaarensis (black samsum ant). Used with permission of Mike J. Lush, sifolinia. blogspot.com, 2009.
Electron microscope image of the stinger of Pachycondyla sennaarensis which injects allergenic venom. From the Museum of Entomology in Department of Zoology, College of Science, King Saud University, Riyadh, Saudi Arabia (Courtesy of Dr. M. Khalifa).
The imported fire ant is a significant health problem in the southern United States.2
The venom from fire ants contains several allergenic proteins, which can cause anaphylaxis in allergic individuals. The safety and effectiveness of several immunotherapy options have been documented for fire ant stings.9,10
However, research has shown that patients who have had an anaphylactic reaction to a Pachycondyla
species ant might not benefit from immunotherapy with an imported fire ant extract.10
Immunotherapy with the extract of Pachycondyla
species ants is expected to be highly effective. Ant venom immunotherapy is feasible and highly efficacious.10
However, the limited geographical distribution of each species presents a major challenge to making venom extracts available for clinical use.12
In this study we confirmed the exact species, the venomous nature of its sting and the range of clinical manifestations associated with black ant stings. The acute emergency treatment depends on the manifestation that develop. The acute treatment is summarized in . Patients need to be followed-up by AN immunologists for these cases to be managed appropriately and to document if they develop secondary reactions. The cases were referred to primary health care in this case series prior to documenting that the cause of the allergy was an ant bite.
Simple algorithm for treating patients presenting with acute anaphylaxis.
The study of ant allergy in Asia and the Middle East is in its infancy. Clinicians in these countries need to be aware of ant stings as a cause of severe allergic reactions. Certain species that cause allergic reactions deserve further research. The allergens in the venom of the different ant species need to be identified. We should aim for improved understanding of the epidemiology of ant-sting anaphylaxis, formulation of better diagnostic tests and possibly the introduction of immunotherapeutic strategies. We believe these types of studies are required to find an effective treatment or prophylaxis against ant stings as it is a health hazard that can lead to severe morbidity and mortality. This study confirms that public health problems due to severe ant sting anaphylaxis in this region are due to the ant species Pachycondyla sennaarensis (samsum ant).