Mosquito-borne disease in New Zealand

This surveillance report presents information on how the health of New Zealanders is affected by exotic mosquito-borne diseases such as dengue fever and malaria between 2001 and 2021.

Key facts

• Mosquito-borne disease cases decreased in New Zealand in 2020 (74 cases) and 2021 (16 cases) after an average of 284 cases per year from 2015–2019.
• Pacific Island and African countries were common travel destinations for individuals returning to New Zealand with mosquito-borne diseases in 2021.
• There were no known cases contracted locally; all cases were caught overseas before returning to Aotearoa, New Zealand.
• Mosquito-borne disease rates were highest for males, and individuals aged 15-34.

Background information

Certain exotic diseases pose a greater risk to the public health of Aotearoa New Zealand because:

• individuals are not immune as the disease is not found naturally in New Zealand and no vaccines are readily available.
• they spread easily and are often difficult to identify.
• they can cause serious illness and can be difficult to treat.

High-risk exotic diseases include:

• vector-borne diseases, especially those spread by mosquitoes which cause chronic suffering and life-long morbidity and disability. These often have no or mild symptoms, often making it difficult to determine the true burden of disease (Duffy et al 2009).
• Public Health Emergency of International Concern diseases as classified by the World Health Organisation (see Overseas infectious diseases of concern for more information).
• Respiratory diseases can cause serious lung infections (eg, influenza, COVID-19).

Emerging and known international diseases of concern to New Zealand require ongoing monitoring and evaluation. This process reduces the risk associated with the ever-changing infectious disease environment seen globally (Bloom and Cadarette 2019).

COVID-19 travel restrictions cause mosquito-borne disease cases to plummet 

In 2021, 16 cases of mosquito-borne disease (MBD) cases were reported in New Zealand. These included: two mosquito-borne viral diseases, seven cases of dengue fever and one case of Ross River fever, and one mosquito-borne parasitic disease, malaria (eight cases). In comparison, there were between 224-349 cases per year during 2014–19. (Figure 1). Prior to 2014 total MBD cases ranged from 44–193 cases per year, with the increase in 2014 linked to Zika, chikungunya and dengue outbreaks overseas.

Figure 1: Number of case notifications of mosquito-borne diseases in New Zealand, 2001-2021

Source: ESR 2023

All mosquito-borne disease cases acquired overseas

From 2019–21, all people diagnosed with a MBD were thought to have acquired it while travelling overseas (ESR 2023). Many cases had travelled to multiple countries, all of which are recorded in Table 1. It is often not possible to determine a specific country of origin when individuals have travelled to multiple countries, therefore all are counted.

Table 1: Locations visited by New Zealand travellers prior to diagnosis of a mosquito-borne disease, 2019–21