Brown rats (Rattus norvegicus) are synanthropic rodents with worldwide distribution, which are known to harbour many zoonotic pathogens and parasites. No systematic zoonotic surveys targeting multiple pathogens and parasites have previously been conducted in urban rats in Finland.

In Helsinki, Finland, we explored the presence and prevalence in brown rats of certain pathogens and parasites (including helminths, viruses and bacteria) across potentially zoonotic taxa.

We opportunistically received rat carcasses from pest management operators and citizens from 2018 to 2023. We searched for heart- or lungworms, performed rat diaphragm digestion to check for Trichinella and morphologically identified intestinal helminths. We assessed virus exposure by immunofluorescence assay or PCR, and detected bacteria by PCR (Leptospira) or culture (Campylobacter).

Among the rats investigated for helminths, no heart- or lungworms or Trichinella species were detected and the most common finding was the cestode Hymenolepis nana (in 9.7% of individuals sampled, 28/288). For some of the surveyed virus taxa, several rats were seropositive (orthopoxviruses, 5.2%, 11/211; arenaviruses, 2.8%, 6/211; hantaviruses 5.2%, 11/211) or tested positive by PCR (rat hepatitis E virus, 1.8%, 4/216). Campylobacter jejuni (6.6%, 17/259) and Leptospira interrogans (1.2%, 2/163) bacteria were also present in the rat population examined.

Prevalences of potentially zoonotic pathogens and parasites in brown rats in Helsinki appeared low. This may explain low or non-existent diagnosis levels of rat-borne pathogen and parasite infections reported in people there. Nevertheless, further assessment of under-diagnosis, which cannot be excluded, would enhance understanding the risks of zoonoses.

Outbreaks of highly pathogenic avian influenza (HPAI) on poultry farms and in wild birds worldwide persists despite intensified control measures. It causes unprecedented mortality in bird populations and is increasingly affecting mammalian species. Better understanding of HPAI introduction pathways into farms are needed for targeted disease prevention and control. The relevance of airborne transmission has been suggested but research involving air sampling is limited and unequivocal evidence on transmission routes is lacking.

We aimed to investigate whether HPAI virus from wild birds can enter poultry houses through air inlets by characterising host materials through eukaryote DNA sequencing.

We collected particulate matter samples in and around three HPAI-affected poultry farms which were cleared and decontaminated before sampling. Indoor measurements (n = 61) were taken directly in the airflow entering through air inlets, while outdoor air samples (n = 60) were collected around the poultry house. Positive controls were obtained from a bird rehabilitation shelter. We performed metabarcoding on environmental DNA by deep sequencing 18S rRNA gene amplicons.

We detected waterbird DNA in air inside all three, and outside of two, poultry farms. Sequences annotated at species level included swans and tufted ducks. Waterbird DNA was present in all indoor and outdoor air samples from the bird shelter.

Airborne matter derived from contaminated wild birds can potentially introduce HPAI virus to poultry houses through air inlets. The eDNA metabarcoding could assess breaches in biosecurity for HPAI virus and other pathogens potentially transmitted through air via detection of their hosts.

After most COVID-19 pandemic control measures were lifted in 2022, many infectious diseases re-emerged. An increase in invasive group A streptococcal (iGAS) infections among adults and young children was reported by several countries. Viral infections including influenza and varicella, known risk factors for iGAS infection, also increased.

To estimate the proportion of GAS skin and soft tissue infections (SSTI) and pneumonia/sepsis in children (≤ 5 years) attributable to varicella, and the proportion of GAS pneumonia/sepsis in children and adults attributable to potentially predisposing respiratory viruses influenza A and B, RSV, hMPV and SARS-CoV-2 in the Netherlands.

We performed time series regression using weekly data on respiratory viruses, varicella and non-invasive GAS infections and GAS isolates cultured from blood, lower airways, skin, pus and wounds, from January 2010 to March 2023.

In 2010–19, 50% (95% CI: 36–64) of GAS SSTI in children were attributable to varicella. Between January 2022 and March 2023, 34% (95% CI: 24–43) of GAS SSTI cases were attributable to varicella. Of iGAS pneumonia/sepsis between January 2022 and March 2023, 34% (95% CI: 20–49) and 25% (95% CI: 18–32) was attributable to respiratory virus infections in children and adults, respectively, with the largest contributor (17%) being influenza A.

Predisposing viral infections likely contributed to, but cannot fully explain, the observed iGAS increase among children and adults in 2022–23 in the Netherlands. Public health measures to control viral infections, such as vaccination against varicella or influenza, might reduce the iGAS disease burden.