Clinical Profiles

Introduction. Parachlamydia acanthamoebae is an obligate intracellular bacterium related to disease-causing bacteria like Chlamydia trachomatis and Chlamydia pneumoniae and is thus classified within the Chlamydiales order. Parachlamydia was initially discovered within an Acanthamoeba strain isolated from water in a humidifier during an investigation of an outbreak of respiratory infections in humans.

Gap Statement. The disease-causing potential of this bacterium is not fully understood, but Parachlamydia has been associated with bronchiolitis, bronchitis, aspiration pneumonia and community-acquired pneumonia in humans. Additionally, diagnostic testing for Parachlamydia infection is not routinely performed, indicating that prevalence is underreported.

Aim. This JMM profile aims to gauge what is currently known about the pathogenic potential of P. acanthamoebae and bring awareness to gaps in knowledge.

Results. Amoebae appear to be the main reservoir of P. acanthamoebae and likely enter the nasal passages through contaminated water sources or contact with contaminated animals. The infected amoebae may then descend to the lower respiratory tract where the lytic cycle is triggered, causing human infection.

Conclusion. By implementing serology and molecular testing, as well as conducting additional epidemiological studies, a better understanding of the association of human colonization with disease outcomes can be achieved.

Infectious bronchitis virus (IBV) is a highly contagious avian Gammacoronavirus that affects mainly chickens (Gallus gallus) but can circulate in other avian species. IBV constitutes a significant threat to the poultry industry, causing reduced egg yield, growth and mortality levels that can vary in impact. The virus can be transmitted horizontally by inhalation or direct/indirect contact with infected birds or contaminated fomites, vehicles, farm personnel and litter (Figure 1). The error-prone viral polymerase and recombination mechanisms mean diverse viral population results, with multiple genotypes, serotypes, pathotypes and protectotypes. This significantly complicates control and mitigation strategies based on vigilance in biosecurity and the deployment of vaccination.

Rift Valley fever (RVF) is caused by infection with Rift Valley fever virus (RVFV), a mosquito-borne RNA virus that affects both humans and livestock species. Humans can also acquire infection from contact with infected animals and contaminated bodily fluid. Veterinary vaccines are available for use in livestock, but no vaccines have been approved for humans to date. The virus is currently endemic in most sub-Saharan regions of Africa but numerous incursions into Middle Eastern countries and islands in the Indian Ocean, such as Mayotte (an overseas Department of France), have occurred in the past decade. The risk of further geographical expansion is high and therefore additional investigation is warranted to better understand disease transmission and pathogenic mechanisms to develop threat mitigation strategies.

Avian reoviruses (ARVs) have a significant economic impact on the poultry industry, affecting commercial and backyard flocks. Spread feco-orally, or vertically, many do not cause morbidity, but pathogenic strains can contribute to several diseases, including tenosynovitis/arthritis, which is clinically the most significant. The last decade has seen a surge in cases in the US, and due to ongoing evolution, seven genotypic clusters have now been identified. Control efforts include strict biosecurity and vaccination with commercial and autogenous vaccines. Research priorities include improving understanding of pathogenesis and developing new vaccines guided by ongoing molecular and serologic surveillance.

West Nile virus (WNV) is a positive-sense single-stranded RNA virus belonging to the Flaviviridae family and is maintained in an enzootic cycle between avian hosts and mosquito vectors. Humans, horses and other mammals are susceptible to infection but are dead-end hosts due to a low viraemia. The disease can manifest itself in a variety of clinical signs and symptoms in people and horses from mild fever to severe encephalitis and morbidity. There are no vaccines licensed for human protection, but parts of Europe, North America, Africa and Australia have vaccines commercially available for horses.

Usutu virus (USUV) is an emerging arbovirus belonging to the family Flaviviridae, genus Flavivirus. It is maintained in an enzootic cycle, with mosquitos as the vector and birds as the main amplifying host. Humans, and other mammals such as horses, are dead-end hosts. The virus was originally detected in sub-Saharan Africa, but in the past two decades has spread across Europe. In certain bird species, such as the Eurasian blackbird (Turdus merula), USUV is extremely virulent and can be fatal. Human infection is rare and often asymptomatic, but multiple short-term neurological diseases have been reported, highlighting its public-health risk.

Swine influenza is an acute respiratory disease of swine caused by swine influenza A virus (SwIAV). The ability of SwIAV to spread bidirectionally from animals to humans (zoonotic), and from humans to animals (reverse zoonotic), drives coinfection that can result in gene segment exchange and elevates the risk of generating viruses with pandemic potential. Compared to human-origin influenza A viruses, current data indicate a greater diversity amongst circulating SwIAVs, with three major subtypes (classified by haemagglutinin and neuraminidase) circulating globally in swine (H1N1, H1N2 and H3N2). The lack of protection afforded by human seasonal influenza vaccines against SwIAVs exacerbates the risk associated with reassortment of human, swine and potentially avian viruses. As such, global monitoring of SwIAVs is important for both human and animal health as they represent a true ‘One Health’ challenge with pandemic potential.

Japanese encephalitis (JE) is an infection that occurs predominantly in Asia and the Pacific Islands. It is transmitted by mosquito bites, with the main vector being Culex tritaeniorhynchus, and is maintained in enzootic cycles involving pigs, wild birds and mosquitoes. JE is caused by infection with Japanese encephalitis virus (JEV), a zoonotic pathogen that also causes disease in mammals such as pigs and horses. In humans, most symptoms are mild or flu-like but can progress to encephalitis. Pigs are considered amplification hosts, and sows may have gestational complications. Horses may exhibit neurological signs. Detection of the virus can be confirmed by serological or molecular laboratory tests. Vaccination offers protection against JEV infection in humans, pigs and horses. Whilst there is no effective treatment of JE, human cases may require hospitalization for supportive therapy, which may include administration of fluids, oxygen and medication to treat symptoms.

Staphylococcus epidermidis is the most abundant commensal bacterium of human skin. Despite protecting us from foreign invaders, S. epidermidis itself exploits human vulnerability when given the opportunity. Such opportunities arise when patients are immunocompromised or when biomedical implants present an opportunity to colonize the surface and form biofilms. S. epidermidis is one of the most frequently isolated organisms from implanted devices and from bloodstream infections. However, S. epidermidis infections are often recalcitrant to antibiotics because of biofilm-associated antibiotic tolerance. Furthermore, the emergence and spread of nearly pan-resistant strains is a considerable health concern. Symptoms can be subclinical, making diagnosis challenging, and treatment with antibiotics is inefficient. For now, infection prevention remains the best strategy available.